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[Assistant] And that is very important. Spiny. So we can say it's spiny. It's very, it's, it's hard to touch it, right? It's like you're touching pins and needles. Spiny means having sharp points like needles.


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[Assistant] So that's also, that's obviously a very good adaptation for this fish. This fish will protect itself by that. Nobody wants to touch this fish because it could hurt, right? Let's take a look at a video of this fish here.


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[Assistant] Now this is a different type of fish. This is called


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[Assistant] Lionfish. And this is a very poisonous fish. You do not want to touch this fish. You see, it has many spines just like the pufferfish.


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[Assistant] It has many spines sticking up from its body. It doesn't blow itself up. These spines are always there.


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[Assistant] Animals, when they adapt to their wild surroundings, they will have different shapes. And we can see a lot of different shapes even if we just look at shells. Right? Some type of animals in the, uh, in the ocean will use shells


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[Assistant] For their body to protect them and they have a lots of different shapes according to what their needs are.


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[Assistant] Shape is the outer form of something. The outer form.


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[Assistant] So we have a star ship, look, a star fish, we have a star fish that looks like a star shape. We have, uh,


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[Assistant] Okay, when we talk about animals, we can classify animals. We can separate the animals into different groups by what do they eat. So we can separate them. We can put animals in one group or the other. We can classify them.


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[Assistant] One group is herbivores. Herbivores. Now that's a long word, right? Maybe a little difficult to pronounce. Herbivores.


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[Assistant] Crush the plants and get the juices from the plants because you have to have strong teeth and flat teeth if you only eat plants. You have to be able to crush those plants very well.


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[Assistant] So what are types of herbivores? Horses, as we can see here, squirrels.


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[Assistant] And rabbits, etc. Those types of animals are herbivores. They're not at the top of the food chain. They're not at the bottom. They're in the middle of the food chain. Let's take a look at a video of a horse. Wow. Of a horse. And he's talking, isn't he? Looks like he's talking. But you see the teeth there.


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[Assistant] The teeth are flat. Oh yeaah, it was a good picture here. We can see the flat teeth there. And, uh, of course the horse needs to have strong, uh, flat teeth in order to be able to eat plants. It was very strange. It looked like that horse was talking or angry at somebody. Okay, let's move on. Now.


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[Assistant] What is the other type of animal? We've talked about herbivores. The other type of animal, of course, is carnivore. Before I said herbivores are not at the top of the food chain, they're in the middle. What eats herbivores? Carnivores will eat herbivores. Because carnivores eat other animals. They eat meat. Okay?


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[Assistant] As opposed to herbivores which have very flat teeth, you can see, wow, look at this lion, right? He has very sharp teeth.


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[Assistant] So these teeth are very sharp, and you see, they're matching. On the top and the bottom, they have a sharp tooth here and here, and also on the bottom, we call these teeth, these sharp teeth, especially these long, sharp ones, those are called fangs. F-A-N-G.


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[Assistant] So if an animal has fangs, it has sharp, pointy teeth.


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[Assistant] That it uses to catch and to bite and to kill other animals so that it eats other animals. That's what carnivores have. What are types of carnivores? Lions, tigers, sharks, etc. Of course, these types of animals can be dangerous, right? Let's take a look at a video here.


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[Assistant] Now of course this is a video of a very, uh, majestic, very, uh, impressive looking lion in the wild. Look at his teeth.


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[Assistant] Wow, look at that. You saw his teeth? Look at his fangs. They're very sharp. You have to be very careful.


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[Assistant] Of an animal like this because it could be dangerous, right? They eat other animals. That's what they do. So they could eat you. Be very careful, obviously, if you're around big animals like this, like lions and bears. And of course, if you're underwater, watch out for sharks as well. Sharks, you know, usually will avoid you.


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[Assistant] But you have to be careful what you have in your hands. Okay, let's move on.


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[Assistant] Okay, here let's move on to this exercise, match each word with its definition. So we have the words here, wild, spiny,


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[Assistant] Adaptation. One more time. Adaptation.


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[Assistant] Okay, these are long words so we need to practice the pronunciation a little bit.


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[Assistant] Let's look at the definitions. Number one, having sharp points like needles. Remember the picture of the fish we saw before? The fish had very, uh, sharp points coming off of its body like needles.


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[Assistant] So we could say that that fish is what? We're looking for an adjective. We're looking of course for


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[Assistant] An animal that only eats plants. Remember, this is an important part of the lecture. We're talking about two kinds of animals. We can classify animals.


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[Assistant] One type of animal that only eats plants, it's a little hard to pronounce, do you remember? It's an herbivore. Herbivore. A good way to remember that is an herb


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[Assistant] Is a type of plant, right? So an herb, it's an herbivore. Of course, it doesn't just eat herbs, it eats all kinds of plants, right? But an herb is a type of plant, so that's a good way to remember.


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[Assistant] A body part that helps a living thing meet its needs. So remember we talked about this word a little bit. We talked about an animal that changes parts of its body in order to meet its needs. Like the giraffe will grow a very long neck.


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[Assistant] Number four, an animal that only eats meat. We saw herbivore before is an animal that only eats plants, like an herb, but what is an animal that only eats meat? Well of course that would be a carnivore. Carnivore. Okay?


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[Assistant] Number five, the color or shape of an animal that helps it to hide. Remember when an animal wants to hide in the environment, like those white wolves in the snowy background, they can hide very well because they have camouflage. The color or shape.


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[Assistant] That protects it. They can hide in their environment. That is camouflage.


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[Assistant] Number six, living or growing in a natural habitat. In a natural habitat. Not in your home, not in a zoo. They are living out in the


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[Assistant] Wild. So if something lives out in the wild, they are living in the natural habitat. Nothing man-made. Not in a home, not in a zoo, not in a cage. They are living in the wild.


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[Assistant] Okay, let's move on here. Okay, let's take a look at our chart here. Remember we were just talking about camouflage. Camouflage is when an animal changes its color or shape. Changes, it has an adaptation


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[Assistant] Uh, to hide in its environment. So it uses color or shape to hide in where it lives.


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[Assistant] Now some animals, you know, they do a little bit, maybe they change the color of their fur from the winter to the summer.


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[Assistant] But some animals are really good at this. We can call them geniuses, right? They're the genius animals of camouflage. They're really, really good at this. Let's take a look at some examples.


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[Assistant] Insects of course are very good at camouflage. Insects are the masters at camouflage.


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[Assistant] Here we have a peppered moth caterpillar. A caterpillar, of course you know, is a little, it's a worm-like insect that changes into a butterfly. But before it's a butterfly, it can't move around a lot. It has to be able to hide in its environment.


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[Assistant] Here we have a picture of a plant. We can see that the plant has a couple of branches. Here's one branch. Here's another branch. Here's a third branch. Oh, is that a third branch? No, that's not a third branch. That is the caterpillar. There's only two branches and it looks like


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[Assistant] It looks like there's a third branch, but no. That branch is actually the caterpillar. Wow! That caterpillar


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[Assistant] If we look at it, right, our first thought is there's only three branches. There's no caterpillar there. That's how good it is at hiding.


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[Assistant] In the next picture, same caterpillar or similar caterpillar, but the color of the plant has changed. Now the plant is green. So the caterpillar is green. And again, it looks like a branch of the plant. So the caterpillars


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[Assistant] Like a genius at being able to hide inside the plant.


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[Assistant] In the next picture we have a flower mantis.


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[Assistant] Now, I'm sure you've probably seen a mantis before. They're very common in nature.


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[Assistant] These insects, of course, they have the triangular head with the two eyes, and they have the arms that are folded like this. That's why we call it usually a praying mantis, because it looks like it's praying. But it has the arms that are folded like this, and it uses those arms to catch other insects. There is a mantis in this picture. Can you see it?


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[Assistant] Here we have, uh, a flower here. Very colorful flower. Another flower here. And what's this?


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[Assistant] This is the mantis. You can see the body here, right? You can see the body here. You can also see the head over here. And this is a very big head and you can see some arms or legs tucked in there. But it's very hard to see this mantis. It's a genius at hiding among these flowers.


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[Assistant] Down here we have the gum leaf grasshopper. Gum leaf because it looks like a gum leaf, the type of plant. Can you see the grasshopper?


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[Assistant] It's a little hard to see. The grasshopper's body not only is it the same color as the plant it's hiding on, it even has the same pattern. It looks like a leaf because of the pattern on its body. It looks like a gum leaf.


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[Assistant] So this caterpillar, if it's in, in, on the ground, it just looks like an ordinary leaf. A bird will pass right by, won't even notice that grasshopper. Of course that's what most insects are hiding from, birds. And that's why insects are such good


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[Assistant] A hood, of course, is something that you put over your head, right, to protect you from the rain or cold. Can you see the hooded grasshopper here?


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[Assistant] We see leaves of the, uh, of the, uh, plant here. Wait a minute, what is this? This looks like a leg. There's another leg here. Oh, and this looks like an eye, right? And look at that, that's the hood right there. That hood is so big, and it's


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[Assistant] So this hooded grasshopper is using camouflage to look like a leaf of the plant so it's very difficult to see it right away when we look at this plant.


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[Assistant] So as I said before, insects are masters at camouflage. Let's take a look at a video of an insect.


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[Assistant] And as we can see this insect here looks like another example of a mantis.


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[Assistant] Look at him. He's kind of an interesting looking character. He looks like an alien almost. He's got the two eyes, two big eyes on either side. He's got something sticking out of his head. Look at the back.


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[Assistant] That's very interesting. Look at the pattern on the back of this insect. It kind of looks like the shape of the leaves that it's, of the plant that it's on. So this insect blends in.


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[Assistant] Okay, let's take a look at the, uh, at this chart here. We have two pictures. Remember, we were classifying animals into two main groups by what they eat. Okay? So here we have a picture of a lion. Remember, a lion has sharp


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[Assistant] Remember I told you that those are fangs. Sharp pointed teeth. What does this animal eat? This animal eats meat, so it is called a carnivore. This animal eats other animals.


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[Assistant] Over here in our second picture, we have a zebra, right? Look at its teeth. The teeth are, are big and they're flat. They're flat teeth. They're good for eating plants, right? So this animal eats plants, therefore it is an herbivore. Herbivore. Okay?


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[Assistant] Now, let's move on. We have a couple of more, uh, animals. What are they?


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[Assistant] Got a big head, small body. No, it's just the way the picture is, right? Okay. This is a picture of a cow, right? Very funny looking cow. Got horns, ears, and of course we can see the teeth a little bit here. The teeth again are flat, right? They're very flat, but they're thick, they're strong.


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[Assistant] They're flat. What does this animal eat? Of course this animal eats plants. It is an herbivore. Herbivore.


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[Assistant] Finally over here, whoa, look at this guy. He looks dangerous. He looks also fat. He's been eating a lot, right? What has he been eating? If we take a look at the teeth here, there's lots and lots of teeth. Lots and lots of sharp teeth.


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[Assistant] Okay, so what kind of animal is this? It's a carnivore. Okay? So again, these are our two types of animals that we can classify. Carnivore or herbivore. Okay?


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[Assistant] Okay, let's move on to our true-false questions. Number one.


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[Assistant] A carnivore is an animal that only eats plants. Is that true? Does a carnivore eat plants? Remember, a carnivore has sharp pointy teeth.


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[Assistant] Sharp, pointy teeth are not good for eating plants. A carnivore is not an animal that only eats plants. We have to change that. We would have to change that to other animals.


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[Assistant] That's one way we could change it. A carnivore is an animal that only eats other animals or other animals meat, right?


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[Assistant] Okay, uh, of course we could change this. We could say an herbivore is an animal that only eats plants. That would also be correct. But we have to change it. So therefore, this sentence is false.


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[Assistant] Non-living thing. Non means not living. So when we're talking about adaptations, right, we're talking about how animals change. Animals are living things.


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[Assistant] So this is false. If we got rid of nonliving things, then it would be true. An adaptation helps a living thing. That's true. But we have to change the sentence, so it's false. Number three.


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[Assistant] Camouflage helps an animal hide. We saw a lot of examples of camouflage, especially when we were talking about insects. Insects are geniuses at hiding in their environment. They use camouflage. So sure, camouflage helps an animal hide. That is true.


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[Assistant] Okay, well, let's take a break here and we'll move on to the reading in just a minute.


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[Assistant] Okay, welcome back. We're going over the reading section now. And in this reading section, what is our subject? We're talking about adaptations for survival. So that's in our first or topic sentence of the reading passage.


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[Assistant] Adaptations that help them survive.


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[Assistant] So adaptations help them survive. It also helps them meet their needs. So this paragraph is going to be about how animals change or change according to their environment so that they can survive.


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[Assistant] An adaptation is a body part or behavior that helps a living thing meet its need. Whether that need is to get food, whether that need is to be able to sneak up on other animals, or to protect itself from other animals. There's many types of adaptations.


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[Assistant] For example, some animals have spikes, right, spikes all around their body, which are very spiny.


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[Assistant] So this is one adaptation. They have spikes. They grow spikes. Spike is an adaptation. The spikes, they are very spiny.


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[Assistant] Right? They're, they are like needles. If you touch that, OW! It hurts, right? So you gotta be careful.


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[Assistant] What do they do? They protect. They protect the animals. They protect themselves from enemies. So if a shark comes along, the shark does not want to eat this puffer fish because that will hurt. Ow! It's like having a ball of needles. You don't want to eat that, right?


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[Assistant] Wild animals have adaptations. Of course, all animals have adaptations, but wild animals especially need their adaptations because they're living in the wild. Only they can take care of themselves.


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[Assistant] Carnivores, like tigers, have sharp teeth. Sharp teeth?


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[Assistant] Is an adaptation that carnivores use that helps them eat meat, right? Because if they have flat teeth, it's very difficult to, to tear the meat off of another animal with flat teeth. Sharp teeth, they can, they're able to do that.


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[Assistant] So unlike carnivores, not like carnivores, on the opposite side, herbivores have flat teeth for eating plants. So as we saw in the pictures before, herbivores have flat teeth.


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[Assistant] So when we classify the animals, right, we have carnivores and herbivores. Carnivores have adaptations, sharp teeth. That's their adaptation.


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[Assistant] So that they can meet their needs. Herbivores, their adaptation is flat teeth. Flat teeth allows them to eat plants. So two different types of animals, two different styles of adaptations. That's how they change their bodies to meet their needs.


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[Assistant] Camouflage is another adaptation.


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[Assistant] Okay, so it's another adaptation. Camouflage is the color.


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[Assistant] Or shape, right? There's a couple of different ways. We saw how some insects, especially, will change their shape or use their shape to look like the branches of a tree or to look like the leaves, the shape of the leaves, or to look like a flower.


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[Assistant] So they'll also use shape of an animal that makes it blend in. I taught you this word before. Blend in with its environment. So if something blends in with the environment, it is using camouflage. Camouflage is an adaptation.


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[Assistant] A chameleon. A chameleon is a type of lizard, right? A chameleon is really amazing. It can change the color of its body so that it cannot be seen easily. And it can change its body color


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[Assistant] Now he looks like a very scary looking, uh, lizard, right? Very interesting looking lizard. He's got a big mouth here. Right now he's green because he's in a tree that has green leaves. Okay? Now this is a chameleon. You can almost see he's changing from green to yellow over here.


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[Assistant] Look at how the color of his skin or his body changes. And look at the different colors here.


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[Assistant] Here we have dark green. Here we have more of a yellowish green. And he can change these colors. And look at that. There's these horns on the, on the front of the lizard. Very interesting looking, uh, critter. Very interesting looking, uh, creature. But this lizard can actually change the color of its skin.


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[Assistant] Compare and contrast. So we're comparing things. How are they the same?


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[Assistant] We're talking about how adaptation is alike, how adaptation is different. Our words down here, we need to fill in these blanks with these words. We have a lot of blanks. Our words are spiny, survive, herbivores, herbivores, carnivores,


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[Assistant] Carnivores. Shape and needs. So let's take a look at this chart. Adaptation. How is adaptation, how is adaptation alike for all animals? Well, adaptation helps living things to beep and meet their beep.


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[Assistant] So, it helps living things to what? To do what down here?


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[Assistant] Probably survive. Survive is our correct answer. Survive is a verb. They need to survive. They need to continue living. Adaptations help animals.


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[Assistant] Okay, how are adaptation different? How is adaptation different? Different animals use adaptation in different ways.


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[Assistant] Beep. Spikes. What kind of spikes? We're looking for an adjective, right? So we're looking for a word like spiny. Some living things have spiny spikes on their body, right? Spiny. If you touch them, it's like you're touching a needle. Ow! Be careful, right? Spiny spikes.


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[Assistant] Here, some animals have special color or beep that help them hide. Remember when we talked about camouflage, we talked about color and we also talked about another way that animals use camouflage, color and


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[Assistant] Shape, right? Color and shape that help them to hide in nature. So it's not just color, it's also the shape of their bodies. For example, the caterpillars, their shape looks like a twig or a branch of the plant that they are on.


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[Assistant] Now here we have a blank, have sharp teeth. So we're looking for some kind of animal that has sharp teeth. What kind of animal has sharp teeth? If you chose carnivores, you would be correct. Remember, carnivores, their adaptation is sharp teeth, so that they can eat other animals.


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[Assistant] Now another type of animal has flat teeth. They have flat teeth so that they can eat plants. What kind of animal eats only plants? That would be herbivores.


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[Assistant] So these are different animals, different types of animals, different types of adaptation. Some animals have spike, spiny spikes. Not all animals, right? But some.


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[Assistant] Some animals have color or shape to hide themselves. Not all animals, but some. That's how they're different.


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[Assistant] And of course, the big difference between the two types of animals, some animals eat other animals, some animals only eat plants. So that's another big difference. That's how they are different. Okay, let's go over the reading comprehension questions here.


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[Assistant] Here we have the first question, a chameleon can change what to help it hide?


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[Assistant] What can it change to help it hide? We have here shape, color, or spikes. Remember the chameleon was that strange looking lizard we saw in the video. It had horns on its head.


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[Assistant] Those horns, by the way, you could say are like spikes. Can it change its horns or its spikes?


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[Assistant] No, those horns stay the same, so C is not right. Can it change its shape? Can a chameleon change the shape of its body?


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[Assistant] No, the chameleon can't change the shape of its body, but what the chameleon can do is change its color.


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[Assistant] Remember we saw part of it was green, part of it was yellow. So the chameleon can change the color of its skin to hide depending on where it is. Okay, so let's move on to number two.


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[Assistant] Herbivores. Herbivores. Remember, animals that eat plants. They have beep for eating plants, right? What do they have? Remember, all the answers show teeth. Teeth. Teeth.


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[Assistant] So we're looking for what type of teeth are they? Do they have flat teeth, spiny teeth, or sharp teeth? By the way, it's interesting to note that spiny and sharp mean the same thing.


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[Assistant] Spiny and sharp, right? The, the fish that we saw has many, uh, spikes on it. They're very spiny. They're very sharp. If you touch them, ow! It's like touching a needle. So spiny and sharp are really


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[Assistant] Adaptations help animals meet their needs. What does an animal need? It needs to eat and it needs to live, right?


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[Assistant] The other choice is changing its environment. Can an animal change its environment? No. The environment is not a choice, right? The animal has to live in the environment and an adaptation doesn't help the animal change that environment. It has to live in that environment. See, by protecting it from camouflage,


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[Assistant] You're, animals are not afraid of camouflage, right? Camouflage helps animals protect them from other animals. They're not protected from camouflage. That's silly. The only one choice that makes sense is A. Moving on to number four.


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[Assistant] Herbivores do not eat meat, right? They only eat plants, right?


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[Assistant] Tiger- carnivores eat tigers? No, tigers are at the top of the food chain. Nothing eats tigers, so A is not correct. What about B?


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[Assistant] And chameleons can change a plant's color, so chameleons can change the color of the plants? No. Chameleons change their own color to blend in with the plants. So B is not correct. C must be your answer. Herbivores do not eat meat and carnivores do not eat plants.


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[Assistant] Okay, let's move on to our chart here. Remember, we're classifying animals into two main groups by what do they eat. Over here we have a picture of a horse.


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[Assistant] Animals like horses have flat teeth because they only eat plants. Examples, horse, squirrel, and rabbit. What classification is this animal? What classification do we put it in? This animal is an herbivore. These animals are herbivores. Down here we have a picture of a lion.


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[Assistant] Lions and other animals like this have sharp pointed teeth, right? They have sharp teeth. They eat other animals. Examples, lion, tiger, shark. These animals are at the top of the food chain. What do we call these animals? We call them


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[Assistant] Carnivores. So if you chose that, that is correct. Okay, well that wraps up this lesson. Uh, it's very interesting to look at animals, how they have changed to meet their needs. We call those adaptations. And that's what we have learned in this lesson. Hope you've learned a lot. We'll see you next time. Take care.


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[Assistant] If there's anything we've seen so far in this series, it's that you need the right materials to solve your problems. Metals and ceramics will go a long way in this world, but they're not always the best choice. Every time you bounce a ball or drive a car on a set of tires, you're seeing a different kind of material in action.


[User] Please transcribe this text

[Assistant] A class of molecules that can react with others to form much larger molecules. In a polymer, monomers are repeated over and over again until there are hundreds, thousands, or even millions of them in a long line. Typically, polymers have lower densities compared to metals and ceramics, and they aren't usually as stiff or strong.


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[Assistant] These are often called elastomers, and are mainly found in rubber materials. Take a rubber band, for example. The molecules in the polymer can be all clumped together.


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[Assistant] It's the stuff used to make things like tires, like the ones you might find on a fire truck. Well, vulcanization is the process of using sulfur to cross-link and strengthen rubber polymers. Tires probably aren't the only polymers you're familiar with.


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[Assistant] Chances are good that you use plenty of them every day, like the ones you'll find in plastic bags and seat covers. And while it's easy to take polymers for granted, they've only been widely used since about the 1940s.


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[Assistant] But that doesn't mean they don't have a special place in history. Research suggests that the first time people really used polymers was back in pre-Columbian Mexico and Central America.


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[Assistant] And then you just combine that with some cornstarch. Stir them together, roll it around in your hand, and poof!


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[Assistant] And when the billiard balls hit each other just right, they would explode on the pool table, which happened quite often. Today, billiard balls are still made of polymers, just ones that are far less explosive. We also tried using cheaper, more flammable substitutes for silk back in the day.


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[Assistant] Help drive the polymer industry into existence, especially the creation of synthetic polymers. During the war, the Allies used polymers to create large inflatable tanks that served as decoys on the battlefield.


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[Assistant] I'd call that a win for polymers. And a win for us engineers, because they set us up for the world of polymers that we have today. It's this world that helped us keep firefighters safe, using polymers to design better gas masks.


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[Assistant] It's primarily found in packaging materials like plastic bags and bottles. Polyvinyl chloride comes in two main forms, rigid and flexible. Rigid forms of PBC are often used in buildings and construction for things like plastic pipes and the frames for windows and doors.


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[Assistant] They need to be strong, not just for daily use, but to hold up for as long as possible in a disastrous event like a fire. PVC can also be made softer and more bendable by adding in a plasticizer, which can help it be more flexible or make it less thick and viscous.


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[Assistant] You'll find flexible PVC in imitation leather, flooring, and inflatable products. Polyethylene terephthalate is a bit different.


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[Assistant] That's called polymeric drag reduction. The end result is a fluid that can flow even faster with the same pressure behind it. Which is really important if your fire hose can only safely reach the 10th floor and you have a fire on the 12th. So now we have a way to solve our problem! Add in a small concentration of polymeric material, and voila!


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[Assistant] And with one as high up as this, they'd likely try to find a different solution, like trying to attach a hose to an adjacent building. But as a thought exercise, it's a great way to see some of the more innovative uses of polymers and what they can do. Today we learned all about the third main type of material that you'll encounter as an engineer – polymers.


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[Assistant] Then we saw the strange history of polymers, and what led to how we use them today.


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[Assistant] Crash Course is a Complexly production and this episode was filmed in the Doctor Cheryl C. Kinney Studio with the help of these wonderful people and our amazing graphics team is Thought Cafe.


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[Assistant] I understand. Don't worry, I will compensate you both.


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[Assistant] I never expected that those treasure hoarders would have their eyes on the same ruins that I had. Before I knew it, they'd caught and imprisoned me.


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[Assistant] Of course we do. How can one sell antiques without gift boxes?


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[Assistant] This palace floats in the skies. Higher than the peak of any mountain.


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[Assistant] And since becoming the Tianxuan, I have spared no effort in hiring the best craftsman to constantly extend it.


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[Assistant] You two are very interesting people, after all. It would be natural to take an interest.


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[Assistant] 1B, Unit 4, Apple.


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[Assistant] Red Juicy Juicy Juicy


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[Assistant] Boss, where do you want these spheres and cubes? Just dump them over there for now.


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[Assistant] Who put these spiky cones on the road? I almost got a flat tire.


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[Assistant] Just don't pay attention to him. He always thinks he is better than the rest of the monster trucks.


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[Assistant] Six Kiwis. One, two, three, four, five, six.


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[Assistant] No, he wiped my face with a planet while the Bleaker Street Magician gave away the store. That's what happened. There was no fight. Okay. He said people. Did he give you any clues? Any coordinates? Anything?


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[Assistant] Was a pseudo-armor around the world, remember that? Whether it impacted our precious freedoms or not. That's what we needed. Well that didn't work out, did it? I said we'd lose. You said, we'll do that together too. And guess what Cap? We lost. And you weren't there. But that's what we do, right?


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[Assistant] I saw this coming a few years back. I had a vision. I didn't want to believe it. That was a dream. Tony, I'm gonna need you to focus. And I needed you. As in past tense. That trumps what you need. It's too late, buddy.


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[Assistant] Because I needed you. As in past tense. That trumps what you need. It's too late, Marty.


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[Assistant] Was a pseudo-armor around the world, remember that? Whether it impacted our precious freedoms or not. That's what we needed. Well that didn't work out, did it? I said we'd lose. You said, we'll do that together too. And guess what Cap? We lost. And you weren't there. But that's what we do, right?


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[Assistant] Here, take this. You find him. You put that on. You hide.


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[Assistant] No, he went in my face with a planet, while the bleaker street magician gave away the store. That's what happened. There was no fight. Okay. He said people. Did he give you any clues? Any coordinates? Anything?


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[Assistant] Was a pseudo-armor around the world, remember that? Whether it impacted our precious freedoms or not. That's what we needed. Well that didn't work out, did it? I said we'd lose. You said, we'll do that together too. And guess what Cap? We lost. And you weren't there. But that's what we do, right?


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[Assistant] Here, take this. You find him, you put that on. You hide.


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[Assistant] E-L-E-P-H-A-N-T Elephant Now you read


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[Assistant] In classical Newtonian physics, the Lagrangian of a system is the total kinetic energy minus the total potential energy.


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[Assistant] And the equation for the Lagrangian at each point in time is a function of all the fields throughout all of space.


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[Assistant] We could be dealing with Einstein's theory of relativity, or with quantum field theory, or with Newton's laws of motion.


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[Assistant] When physicists propose new fundamental laws of physics,


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[Assistant] They often do so by proposing a new equation for the Lagrangian. What we therefore want to focus on


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[Assistant] But how the Lagrangian is used to predict the behavior of a system.


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[Assistant] As this has universal practical and philosophical importance.


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[Assistant] Suppose we know the initial state and the final state of a system.


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[Assistant] We wish to calculate the path between the initial and the final state.


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[Assistant] The system can consist of any number of fields and particles, and the system can contain any number of independent variables.


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[Assistant] The variable X could refer to the position of a particle along one dimension.


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[Assistant] In order to calculate the future behavior of a system, we need to know both the position and the velocity.


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[Assistant] We will refer to the velocity in the X direction using the symbol X with a dot over it.


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[Assistant] Suppose we have a function that depends on both the position and the velocity.


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[Assistant] The Lagrangian is also a function of all the other independent variables.


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[Assistant] This graph could also be a function of time.


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[Assistant] For the following animations, we will show a graph that does not change with time.


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[Assistant] We don't know the path between the initial and final state.


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[Assistant] But let's propose one possible path as a guess.


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[Assistant] The height of the red ball at each point in time symbolizes the value of the Lagrangian at each point in time.


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[Assistant] Here, the color symbolizes the value of the Lagrangian.


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[Assistant] Time is not shown on this graph, but we can change the graph so that it shows the value of the Lagrangian as a function of time.


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[Assistant] Let us say that the region in red is considered to have a negative area.


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[Assistant] And the region in green is considered to have a positive area.


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[Assistant] If the path changes, then the action also changes.


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[Assistant] If we are dealing with physical laws where the total work done depends only on the initial and final state of the system, and not on the path in between,


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[Assistant] Then the true actual path of the system must be at a point where the slope of this graph is zero.


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[Assistant] For this reason, people often refer to using this method to find the path as the principle of least action.


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[Assistant] However, a more accurate description would be the principle of stationary action, since the actual path needs to be at a point where the slope of this blue line is zero.


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[Assistant] The slope of this line is the partial derivative of the Lagrangian with respect to x.


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[Assistant] Here, the color represents the partial derivative of the Lagrangian with respect to x.


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[Assistant] Let us now view this as a function of time.


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[Assistant] Let's change the vertical position of each ball based on its color.


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[Assistant] The partial derivative of the Lagrangian with respect to x.


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[Assistant] This is just one of the partial derivatives we can have.


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[Assistant] We can also have the partial derivative of the Lagrangian with respect to the variable symbolized by the x with the dot over it, which we will call x dot.


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[Assistant] The color represents the partial derivative of the Lagrangian with respect to x dot.


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[Assistant] Let's change the color of each ball to match the color of the graph at the ball's location.


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[Assistant] Let's change the vertical position of each point based on its color.


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[Assistant] We now have as a function of time, the partial derivative of the Lagrangian with respect to x dot.


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[Assistant] Let's represent the slope of this function of time with a new set of colors.


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[Assistant] Let's again change the vertical position of each point based on its new color.


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[Assistant] We now have this new expression as a function of time.


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[Assistant] We are now ready to use these expressions to find the path of the system.


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[Assistant] For the slope of the blue line to be zero, this expression must also be equal to zero.


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[Assistant] The slope of the blue line being zero means that the action will stay about the same for any exceedingly small change in the path.


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[Assistant] Therefore, the amount by which the action will increase is also equal to this amount.


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[Assistant] Consider how the velocity of this curve has changed.


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[Assistant] The velocity of this curve is represented by X dot.


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[Assistant] Here, the Lagrangian for one point goes up.


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[Assistant] And the Lagrangian of the other point goes down by an equal amount, resulting in no net change in the total action.


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[Assistant] But let's now consider a case where the partial derivative of the Lagrangian with respect to x dot is not the same at these two points.


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[Assistant] Now both of the points will go down, resulting in a decrease in the total action.


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[Assistant] The decrease in the action is the rate at which the partial derivative of the Lagrangian with respect to x dot is changing with time.


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[Assistant] Therefore, the total change in action is equal to the equation we saw earlier.


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[Assistant] Then this means that the change in action is zero for any exceedingly small change in the path.


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[Assistant] And this happens only for cases where the slope of the blue line is zero, which must be the case for the true actual path.


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[Assistant] The variable x dot represents the partial derivative of the variable x with respect to time.


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[Assistant] This equation must also be true for any independent variable of the system.


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[Assistant] And there is no limit to how many independent variables a system can have.


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[Assistant] If we are dealing with quantum field theory, we will have a variable representing each of the fields throughout all of space.


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[Assistant] And we have to take into account not just the partial derivatives with respect to time.


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[Assistant] But also the partial derivatives with respect to each of the spatial dimensions.


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[Assistant] Here, the initial and final conditions are the quantum fields throughout all of space at two different points in time.


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[Assistant] And the equation below must be zero for the description of how each quantum field evolves through time.


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[Assistant] But visualizing quantum field theory is a topic for another video.


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[Assistant] Much more information is available in the other videos on this channel. And please subscribe for notifications when new videos are ready.


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[Assistant] Hi Max. We are going to the zoo. Do you want to go too? Just one second. Let me help the shapes. Okay shapes. Circle. Oval. Triangle. Square. Rectangle. Octagon.


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[Assistant] Okay, Mats, let me show them to you. Here we have. Bear.


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[Assistant] Hedgehog, mouse, pig, giraffe,


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[Assistant] These are issues at the cellular level, far too small to solve with any conventional tools. And even if we find a solution to the root problem, the body's own defense mechanisms will often see a potential cure as a threat and attack it. A good example of this is type 1 diabetes, a chronic condition that requires treatment with insulin.


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[Assistant] Some of which can magnify samples by up to 1 million times. Even then, to actually work on the nanoscale, you need something like the scanning tunneling microscope, which not only allows you to see individual atoms and molecules, but also lets you move them around. But don't let the small size of nanomaterials fool you.


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[Assistant] Compared to their larger-scale counterparts, they often have better properties, like increased strength.


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[Assistant] These traits can let you solve new kinds of problems, like protecting those implanted insulin-producing cells I mentioned earlier. The device you'll need to protect those cells will have to have holes large enough.


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[Assistant] That may sound a bit counterintuitive, but if you break something down into smaller chunks, the overall surface area increases. You can see what I mean if you take a block and slice it down the middle. You didn't change the overall mass or amount of material.


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[Assistant] And that contact matters. For example, break a material into nanometer-sized particles, and the increased surface area will lead to a faster rate of any surface-level reactions. This makes nanomaterials great catalysts, or substances that increase the rate of a chemical reaction.


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[Assistant] And it's why they're used in a wide range of important industrial chemical reactions. Nanomaterials are often more attractive to water and oil molecules, making them more absorbent than larger materials. That's why they're used in water treatment plants to remove pollutants, and at sea, to clean up oil spills. We've also found that solid nanoparticles can even act like liquids.


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[Assistant] Not just as some sort of bulk movement, like you might see when a pile of sand acts like a fluid, but in the motion of individual particles themselves. On their outermost layers, only about an atom or two thick, these nanoparticles appear to move about like a liquid.


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[Assistant] Even though their insides are solid, their outsides can change shape and wobble about like a drop of water. If you want to form solid, stable shapes out of nanoparticles, these movements could potentially cause your designs to fail, like losing an electrical connection in a circuit. The nanoscale will even change other properties of a material, like its melting point and fluorescence.


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[Assistant] Or the visible light that it emits. Basically, its color. A great example of this is gold. Instead of the color we're used to seeing in a treasure chest,


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[Assistant] Ones that are designed and produced to help solve problems. There are also naturally-occurring nanomaterials, like volcanic ash or soot from a fire, as well as ones that are produced as byproducts of other processes, like combustion. These are often termed ultra-fine particles, and aren't really what you'll be worried about as an engineer.


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[Assistant] For cleaning up oil spills, making better capacitors for circuits, and even creating artificial muscles. But while nanomaterials seem great, there's one pretty big problem.


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[Assistant] The last thing you want is to create new, unexpected problems. Fear of the unknown isn't a good reason to stop moving forward, but more research is always better. The nanotechnology that could keep implanted cells safe inside your body to treat diabetes


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[Assistant] Finally, we saw that since nanomaterials and nanotechnology are so new to us, we still need further research to fully figure out just how safe they are to use. I'll see you in our next episode, when we'll learn more about biomaterials. Crash Course Engineering is produced in association with PBS Digital Studios. If you want to keep exploring big scientific mysteries by going very…


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[Assistant] With the help of these wonderful people and our amazing graphics team is Thought Cafe.


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[Assistant] Hello and welcome to Crash Course History. I'm John Green. You may know me because I once hosted a series of Crash Course videos on world history, which, depending on your perspective, was either far too Eurocentric


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[Assistant] Or not nearly Eurocentric enough. Well, we're about to get-


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[Assistant] Rather Eurocentric. Mr. Green, Mr. Green, right, I remember- Yeah, you're retired me from the past. I can't play 17 anymore. Anyway, starting today, we're gonna explore the history of Europe, beginning with the closing years of the so-called Middle Ages.


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[Assistant] And ending with Europe's recent and possibly temporary great turn toward political and economic unity. But here at the start, I want to note two things. First, that Europe is a made-up idea. Like, in parts of Eastern Europe, students learn that there are six continents, not seven, because Eurasia is treated as a single landmass on account of it being


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[Assistant] You know, a single landmass. But then, Eurasia is both physically and geopolitically inseparable from Africa, just as North America is from South America. And Australia is more of an island than a continent, and don't even get me started on Antarctica. So in some ways, there are two continents. We don't even completely agree what


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[Assistant] Constitutes Europe, the dividing line is often constructed as the Ural Mountains, which would mean that half of Russia is European and the other half Asian, and is Western Kazakhstan Europe?


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[Assistant] The southeastern border of Europe is also problematic. Is Turkey Europe? And if not, was the Roman Empire a European Empire only when its capital was Rome and not for the many centuries in which its capital was Constantinople? But of course, like many made-up ideas, Europe is also real.


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[Assistant] And in these videos, we'll attempt to introduce you to the big political and economic and military and cultural developments in recent European history.


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[Assistant] The second thing I want to say is that one cannot look at the history of Europe in isolation, because as part of the Afro-Eurasian landmass, Europe has long been in contact and conversation with other parts of the world, and so it's impossible to examine its history in isolation


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[Assistant] In early human history, when bands of hunter-gatherers rarely reached populations of larger than a few dozen, people were relatively independent from those who lived far away from them.


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[Assistant] But the story of humans is in some ways a story of growing connection. Like 3,000 years ago, everything most humans used had been made within their community, from clothing to tools to weapons to jewelry.


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[Assistant] Over time, though, our trade networks and cultural connections expanded, and more of us began to live in cities and to travel between communities. By around a thousand years ago, for instance, Christianity, which was born in the Middle East, had become the dominant religion in Europe.


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[Assistant] And the Catholic Church was certainly extremely powerful, but there were also other religions being practiced. Like, most of the Iberian Peninsula, for instance, was controlled by the Islamic Caliphate of Cordoba, which had arrived from northern Africa. Gunpowder, which was first developed in China, began being utilized in Europe around 1300,


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[Assistant] And the great disease pandemics that reshaped early modern Europe also came from Asia.


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[Assistant] What I'm saying is that even Europe isn't really Eurocentric. We're going to try to emphasize the world's interconnectedness in this series, but any regional history risks isolating itself. So throughout, I hope you'll remember that Europe is a made-up idea and that it is nonetheless real.


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[Assistant] And that the lives of humans in Europe have long been shaped by the lives of humans elsewhere. Our history will begin around the year 1300, with Central Europe a tangle of kingdoms and city-states and the continent in a purportedly dark age.


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[Assistant] Big changes are coming. The absolute devastation of the Black Death.


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[Assistant] A reimagining of the relationship between peasant and lord, and questions about the role of the Catholic Church in political life. But before we get there, I want to flash forwards and backwards.


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[Assistant] In September of 1940, with Europe roiled by the Second World War, an 18-year-old car mechanic named Marcel Rabidat was walking his dog Robot in the countryside of southwestern France.


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[Assistant] The next day, Marcel went to the spot with three friends to explore that hole, and after digging for a while, they found a cave.


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[Assistant] With walls covered with paintings, paintings of horses and bison and even extinct species, it would eventually be established that some of these artworks were at least 17,000 years old.


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[Assistant] Two of the boys who found that cave were so profoundly moved by the artwork they saw that they camped outside the cave to protect it


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[Assistant] Now, there's nothing unique to Europe about very old cave paintings. They've been found in the Americas, in Indonesia, in Africa, in Australia.


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[Assistant] They have not been found in Antarctica, another argument against its continenthood. And don't tell me that continents are about geology, not humans. Who do you think invented continents? Rocks? I will confess to being a little human-centric when it comes to history. Right, but cave paintings are not unique to Europe.


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[Assistant] But what I find fascinating about ancient cave paintings is that they were often made over the course of many thousands of years, as hundreds of generations of humans lived in the same caves.


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[Assistant] Like, the paintings at Lascaux, for instance, were likely created over a span of around two thousand years. For two thousand years, a community of humans lived in this cave.


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[Assistant] But it also isn't a long time, as it represents less than one half of one percent of human history. History, like so much else, changes as our perspective changes. And so as we zoom into the history of Europe, let's not forget that we're zooming in.


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[Assistant] The smiles on their faces, that absolute joy. I want that to be me next.


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[Assistant] Cauliflower puree with a fennel pork tenderloin and a rosemary and apple shoe.


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[Assistant] I've been studying my entire life and I've only recently just become a lawyer, but I'm experiencing this ultimate conflict between head versus heart. And right now, this is my time to follow my heart. I want to cook.


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[Assistant] I love food. I feel like I've been interested in food my whole life.


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[Assistant] My nonna has taught me an incredible amount about food and cooking. She loves real food. She loves food that's home cooked honest and food that makes you feel alive. And that's where I got my passion in food. And then what are we going to eat them with? With your mouth.


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[Assistant] A Cucina Poverty style of topping that you would put on pasta, for example.


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[Assistant] I start to add herbs, I start to add flavorings, lots of olive oil, and then I put that into an oven set at 180 degrees. This dish needs to be perfect because I want to get that apron. I want it so bad.


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[Assistant] The most magical food can transport you and I'm sitting in the countryside in the summer in Italy under the trees at a long table with a linen tablecloth with friends and family and I'm seeing platters of this and joy because that's what this kind of food brings.


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[Assistant] Many of you have put your lives on hold in order to chase your food dream. And for many of you, that food dream starts with getting your hands on one of these five aprons. What are the results?


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[Assistant] The final apron goes to a cook that has shown us two sides of a very promising coin. They cooked a dish that was rooted in history, but presented with utter modernity.


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[Assistant] As sincere thank you so much for putting yourselves on the line and giving Master Chef a shot. You are some of the best home cooks in the country and although this is not the result that you wanted,


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[Assistant] Hi, I'm John Green, this is Crash Course European History, and today it's time to find out what else besides money was behind the competition between Spain and England as they fought it out on the seas and across the globe after 1550.


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[Assistant] That's right, today we get to talk about religion. As you may know, the internet is terrible at engaging in nuanced and thoughtful conversations about religion. But if you think, like, our contemporary religious discourse is bad, just wait until you get a load of 16th century Europe.


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[Assistant] Okay, so over the centuries, the Catholic Church had developed a powerful structure under the Papal Monarchy. Its courts, religious laws, local priests, and a huge bureaucracy of religious officials


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[Assistant] It also had ideas about how the universe worked, and sought to repress those whose ideas were different, as we'll discuss further when we turn our attention to the Scientific Revolution. But in general, Catholic domination of so many aspects of life?


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[Assistant] Produced so much resistance beginning in the early 16th century that European Christianity eventually split into two.


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[Assistant] And then split into like 17,000 competing subgroups. It all starts with Martin Luther, a bright young German man whose father wanted him to become a lawyer, as so many fathers do, so Martin Luther went to law school. But his real concern, even after getting his law degree, was salvation. So he became a devout monk.


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[Assistant] Still though, he was agitated, worried about salvation generally, and specifically about church teachings that faith


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[Assistant] And good works were needed to achieve salvation. For Luther, doing good work seemed a bit like bribery. Like, wasn't full faith in God the important thing? This kind of thinking meant that Luther was on his way to heresy, that is, beliefs that went against the principles of the Catholic faith.


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[Assistant] And the heresy of, for instance, denying the Pope's authority could get you burned at the stake, as John Hughes was in 1415. Now, many of Luther's objections to Church teachings were highly theological concerning beliefs about, say, whether the word repent in the Bible can be said to refer to the sacrament of penance.


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[Assistant] But one of Luther's objections was not nearly that obscure and was much more relevant to ordinary people. Let's go to the Thought Bubble.


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[Assistant] Okay, so in Catholic doctrine, there was a state after death called purgatory, a kind of holding place for souls that are not pure enough to ascend to heaven.


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[Assistant] But not bad enough to go to hell. Souls in purgatory can be purified by prayers from the living, and also purified by torturous afterlife punishment. And in 1517, the pope issued a special indulgence to raise money to continue building the splendid St. Peter's Basilica in Rome.


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[Assistant] Purchasing one of these indulgences was said to release a soul from purgatory, so if you had a deceased family member or friend whose sins might not have been totally cleansed through their faith in good works,


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[Assistant] From this, you could release us with a few alms.


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[Assistant] Why do you treat us so cruelly and leave us to suffer in the flames when it only takes so little to save us?


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[Assistant] I'm not here to criticize any particular religion, but that is a smidge manipulative. It wasn't only Luther who took offense to this practice. Merchants and artisans also noted that it seemed a lot like blackmail.


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[Assistant] Who held high positions in the clergy and lived in luxury without ever having to, you know, earn money.


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[Assistant] Rejection. For we claim the papacy not to be the holy church, Luther stated.


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[Assistant] This rejection of the Catholic Church as it operated in the early 16th century came to be known as the Reformation. Luther began to take on the entire church establishment. In European Catholicism at the time, priests were the authority. They read the Bible and then told you what it said.


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[Assistant] But Luther argued that priests, like all people, were themselves sinners, and that the only true authority was the Bible.


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[Assistant] It was, he argued, the word of God that provided the relationship with God, not the word of priests. He believed that the hierarchy of priests and bishops and cardinals and the pope was inherently corrupt, and that such corrupt individuals could hardly serve as intermediaries with the divine.


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[Assistant] Sola Scriptura, only the Bible or scripture, was his motto alongside the keys to salvation.


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[Assistant] But for everyone, because the written word of God was the way to God.


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[Assistant] I don't get it, it's just a can of mixed nuts, what does that have to do with the diet of worms? OH STAN!


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[Assistant] Right, but back to Charles V. At the time, Charles was 19 years old and ruler of Spain, the Low Countries, and the Duchy of Burgundy, also the entire Habsburg Empire, Italy, all the Spanish possessions in the Western Hemisphere and Southeast Asia,


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[Assistant] Which, I mean, if you've ever met or been a 19 year old, you'll know is a lot of responsibility for someone who cannot legally drink wine in the United States. Although, on the other hand, he does look like he's 50 in this stained glass window of the diet of worms.


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[Assistant] Among those electors was the elector of Saxony, Frederick the Wise, whom Charles had bribed for his vote.


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[Assistant] Frederick was religious, but not a fan of the papacy. And many aristocrats saw Charles as threatening world domination because


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[Assistant] You know, he was dominating a lot of the world. So when called to account by such a massively powerful ruler, everyone expected that an insignificant monk like Martin Luther would completely fold and admit his errors. But he did not.


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[Assistant] I can do no other, he supposedly said of maintaining his new beliefs. The Holy Roman Emperor then declared him an outlaw to be captured, but German princes took his side, and Frederick the Wise hid and protected Luther. Why?


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[Assistant] Well, that remains one of the great unanswered questions of history. Maybe it was because Frederick was genuinely concerned about papal abuses. Maybe because Frederick felt that Luther couldn't get a fair trial. Maybe because he felt that Luther and the reform movements he was leading would limit Charles' power.


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[Assistant] Regardless, after Frederick's death, his brother and successor continued to protect Luther and his followers, helping in 1530 to organize the Schmalkaldic League of Protestant Princes to protect the Lutherans, which, I mean,


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[Assistant] As names go, is no diet of worms. On the other hand, if Marvel's looking for a new superhero franchise, how about the Schmalkaldic League of Protestant Princes?


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[Assistant] Two hundred thousand copies were printed in the 1520s and early 1530s and many more of his other writings went into print. The Reformation went from being local to being German.


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[Assistant] Luther summoned them to defend German values against the corruption found in Rome, and because of that, Luther is sometimes called the source or father of German nationalism.


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[Assistant] And then in 1525, peasants and other village folk across southern Germany began protesting, eventually including an estimated 100,000 rioters who sacked castles as well as religious centers. The princes and nobility crushed them.


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[Assistant] They could get behind religious reform, but not mass social change. And Luther agreed, slamming the rioters in Against the Rioting Peasants, soon reprinted with the new sensationalist title Against the Murderous Thieving Hordes of Peasants. So, you know, Luther favored some reform, but not like


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[Assistant] All the while, the reform movement spread, and as it did, it developed offspring. Already in 1519, Ulrich Zwingli, a Swiss priest, began preaching reform in Zurich, and he supported Luther's main criticisms of the papacy.


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[Assistant] But he disagreed on the Eucharist, or Communion, a Christian ritual in which worshippers eat bread and drink wine.


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[Assistant] Or don't, depending on your perspective. Catholic doctrine held that through the miracle of transubstantiation, the bread and wine literally became the body and blood of Jesus Christ.


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[Assistant] These theological questions were not just a matter of life and death.


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[Assistant] And free will? So only a thinking adult could knowingly participate in the Christian faith enough to accept Jesus as their Lord and Savior?


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[Assistant] So they argued that baptism, a cleansing ritual that had long been performed on infants, should only be available to adults who've chosen to accept Jesus as savior. And as reformers increased in number and variety, Luther did something else that was really shocking. In 1525,


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[Assistant] He got married, even though Catholic clergy were supposed to be celibate. Luther preached that God made two sexes to procreate and that the clergy's celibacy was against the divine plan. So he married Katerina von Bora, a literate young woman who'd been in a convent since the age of five.


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[Assistant] This certainly wasn't equality as we now understand it, what with the wife shining by reason of her husband's raise, but the notion of equity of marital property was heresy piled on top of the heresy of clergy marrying. All of this led to the Holy Roman Emperor Charles V deciding to put down the pesky Protestant princes of the Schmalkaldic League once and for all in 1546 and 1547, and he almost did so.


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[Assistant] Including tough soldiers from the Spanish armies who defeated the league and captured some of the leading Protestant princes.


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[Assistant] But then, in 1552, the League suddenly took to the field again, roundly defeating the Imperial forces. In 1555, the Peace of Augsburg decreed that whoever ruled would determine the religion of his territory. And so communities would be Catholic or Protestant based on the religion of their prince.


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[Assistant] Whew, we really dodged a religious war bullet. Nope!


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[Assistant] No, the Reformation story was not over. Luther had called church corruption a horrid abomination and its defenders excrements and vermin. And those who now entered this titanic religious struggle in other parts of Europe would be just as vehement even if they were following different plots.


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[Assistant] The finer points of theology continued to divide people, as did the politics of religion and overseas empire.


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[Assistant] In short, more bloodshed was to follow. We'll take that up next time. Thanks for watching.


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[Assistant] Thanks so much for watching Crash Course European History, which is filmed here in Indianapolis and produced with the help of all of these nice people. Our animation team is Thought Cafe, and Crash Course would not exist without the generous support of our patrons at Patreon.


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[Assistant] You think Brianna could have done all of that on her own? Not on her own, but... I mean Dylan could have helped her. Jigs! You owe me a coke.


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[Assistant] It can be extremely frustrating, uhm, just, it's very time consuming treating them.


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[Assistant] Uhm, no, I've tried a couple of, uhm, chemistry remedies off the shelf.


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[Assistant] I used the shampoo straight away. Although actually Sophie didn't have any lice at the time. And the effect of it was really good. She didn't get nits for about three weeks after using it. So I think the smell definitely kept them at bay. And in comparison with other treatments, that was a big improvement.


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[Assistant] It seems to be pretty effective. I've never seen Nits look quite so dead before. It did leave her hair in really nice condition. Well, and mine and my daughter's and we all used it. It gave it a really nice sort of chestnutty shine.


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[Assistant] The only downsides of the shampoo were the greasiness and for my children the smell. But I quite liked it. My advice to any other mum who's getting sick of nits and they've tried all the things on the shelf is give this a go. You've got nothing to lose.


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[Assistant] Okay, so Rachel's got 48 and Phoebe has the lead in...


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[Assistant] In this case, a lowly disk of processed meat would nearly tear my family apart.


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[Assistant] That makes it sound like all attempts at engineering are doomed.


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[Assistant] While the outputs that get changed as a result of those observations are called controlled variables. To see all this in action and understand why process control matters, consider cheese. A few years ago, a cheese company based in Toronto ran into trouble when some of the vats they used for storing milk


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[Assistant] Started having problems. The vats needed a certain amount of milk in them for the cheese-making process.


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[Assistant] Like many industrial processes, precision is what allows high-quality products to be manufactured with consistency. And no one wants bad cheese. Too little milk in the tank, and it would affect the production further down the line.


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[Assistant] You might need to write off this production run, but that's not the worst of it. Cheese is made using bacteria. If the milk containing that bacteria...


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[Assistant] was that the inputs to the system of milk fats needed to be controlled to maintain the level of the contents inside. In the language of process control,


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[Assistant] One of the parameters involved in making the product, in this case the level of milk in the tank, is sensitive to the control variables of the process.


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[Assistant] Wasn't working as intended. As we've mentioned, process control uses measurements of a process's parameters to make changes to its controlled variables. That might sound a little abstract, but various types of process control are currently in use around us.


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[Assistant] To keep it at a particular temperature, say, 25 degrees Celsius. That's the set point, the number that represents the target output or operating state you want a process to achieve. For example, after you set it, the thermostat then turns the furnace or the air conditioner on or off.


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[Assistant] To heat up or cool down the environment and maintain it at 25 degrees. The control variable here would be whether the furnace was on or off.


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[Assistant] Which has a direct effect on the parameter you're interested in, the temperature. Other parameters you might want process control to be sensitive to are things like the pressure in an oxygen tank or the force being applied to something. You can even use it to control a mixture's chemical properties, like acidity. Because of its broad uses, process control is everywhere.


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[Assistant] Process control lets you create products to particular standards with consistently high quality and precision. Plus, monitoring and controlling things so carefully can help you find new ways to use materials and energy more efficiently. In modern control systems, measurements are taken as electronic readings from sensors.


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[Assistant] Which are delivered to a computerized control system called...


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[Assistant] Well, the controller. The controller also sends signals to the machinery responsible for changing the controlled variables. This normally means the operation of things like valves or switches. There are two main kinds of process control to consider – feedback and feedforward – which, yes,


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[Assistant] The difference between the observed temperature of the output and the set point is called the error. The controller tries to minimize the error by controlling the inlet valve at the start of the process to increase or decrease the amount of steam entering the exchanger.


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[Assistant] If the error is positive, it will do the opposite. On the other hand, you could also use a feed-forward system. In that case, you'd be measuring the input variables of the process.


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[Assistant] In this case, you'd need to know things like the specific heat of the fluids.


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[Assistant] All the input parameters provide a decent estimate of what the output temperature of the fluid will be. What's more, from the model, you can then work out the best flow rate for the steam.


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[Assistant] Given all the other inputs. In this case, the difference between the measured flow rate and the flow rate needed to obtain the setpoint temperature will be an example of what's called the disturbance. The disturbance is the difference between what the input parameters should be and what they really are.


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[Assistant] Like the output error in a feedback system. All the sensor data is fed forward to the controller.


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[Assistant] Until the inputs are set according to the model, to make the oil's temperature hit the set point. On their own, both of these approaches have some flaws.


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[Assistant] In a feedback control system, you have to wait until something has already gone wrong in order to fix it. If a lot of errors are creeping into the process very quickly, a feedback system might not respond fast enough to change the inputs. On the other hand, a feed-forward system


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[Assistant] Opening the valve might increase the flow rate of the steam by more than you predicted. The cascade control system puts checks in place to prevent that from happening. With the feedback, feedforward, and cascade systems working together in what's called an integrated approach,


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[Assistant] After fixing it to take accurate readings, the factory's process controls started working properly again. And the water in Toronto stayed nice and clean. So while Murphy's law might paint a pessimistic picture of engineering,


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[Assistant] Process control steps in as the linchpin that keeps everything from spiraling out of control. Crisis averted! In this episode, we looked at process control systems, where automated controllers change process variables in response to measured parameters.


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[Assistant] We looked at how feedforward and feedback systems minimize errors and disturbances.


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[Assistant] Check out Global Weirding, which explores the intersection among climate, politics and religion.


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[Assistant] Hosted by climate scientist Katherine Hayhoe. Crash Course is a Complexly production, and this episode was filmed in the Dr. Cheryl C. Kinney Studio with the help of these wonderful people, and our amazing graphics team is Thought Cafe.


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[Assistant] Oh my god. It's superstar week. I'm super stoked.


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[Assistant] Hits me immediately. It tastes like ginger. I cook with ginger a lot. I'm writing down ginger. This is foul.


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[Assistant] Go for it. I'm tasting the biscuit. It's something that is really familiar. I take a smell of it and judging by the color, you know, it's red. I think that it's going to be some sort of dairy, but I can't quite put my finger on it. And I can see Tom, he's already got it.


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[Assistant] Tom and I are in a sudden death tiebreaker together. I'm tasting the biscuit, but I can't quite put my finger on it.


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[Assistant] At this point in time, I'm just gonna have to write down something.


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[Assistant] Not gonna be Therese, Elise or Winona. Up there on the gantry, safe as houses. How we feeling Winona?


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[Assistant] Thousands of dishes that you could make, featuring one of these two ingredients. We're giving you an open pantry.


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[Assistant] Access to the amazing MasterChef garden and 75 minutes to cook your dish.


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[Assistant] I'm Eric, I'm 21 years old and I'm a medical student from Sydney. I'm at hospital today with uhm, lovely colleague.


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[Assistant] Uhm, we're gonna go head to the ward now. Looking like a beautiful day to save lives. So, let's go.


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[Assistant] Cooking is my passion. Regional Chinese cooking is my passion, is my dream, and is where I want to take my life in the future. Eric!


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[Assistant] Hello. Chicken for you first. I'm making a strange flavour chicken. A what?


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[Assistant] So, I cranked the oven all the way up. It needs


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[Assistant] Literally every second it can get to cook through.


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[Assistant] And I'm gonna have time now.


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[Assistant] I have only one television chart I can put on the plate. I'm really worried.


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[Assistant] So today I've made a strange flavored chicken. The idea of it is that it's a


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[Assistant] You've got like the nutty sesame paste, a spiced soy which is aromatic and sweet and salty, sour from the black vinegar, numbing from the citron pepper, and some broth as well to give it a bit of an umami lift.


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[Assistant] Mix it up, yeaah. Yeaah, mix it up, yeaah. Awesome. Very exciting. Can you smell that from here? It's just unbelievable.


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[Assistant] Eric, mate. I'm gonna go out.


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[Assistant] You know why it's so good? Flavour. Like it was everywhere. Your Szechuan oil is just powerful.


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[Assistant] If we're talking chicken here, and we are, you nailed the brief. It's loaded with flavour. Well done, pal. Thank you. Thank you.


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[Assistant] What you didn't do was over or under cook it. Bloody perfect, look at it.


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[Assistant] Oh wow. The best thing about this dish mate is that sauce.


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[Assistant] You cared and loved for and caramelized that sauce. Great chefs make great sauces. Well done mate. Thank you mate.


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[Assistant] It's just the chicken is a little bit dry. Sadly, when you're featuring chicken and the chicken is sort of a cook.


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[Assistant] The bite that I had was mostly eggless. Ah.


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[Assistant] Uhm, so, just take note about what this place can do to you. With time pressure, with MasterChef kitchen pressure, it can just happen. Mate, I'm heartbroken for you.


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[Assistant] Because you are most probably in the bottom five today.


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[Assistant] I'm really disappointed by Federal Bueris and brush it off and get ready for the next round.


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[Assistant] And you know what? Although we were looking for the five least impressive dishes,


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[Assistant] Possibly one of the first hamburgers ever created. They usually stuff it with braised pork, but obviously I'm curing chicken. So, I'm braising down some chicken liquid.


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[Assistant] So, because I want the lemon myrtle to be one of the prominent flavors of my dish, I'm putting in some butter and lemon myrtle underneath the chicken skin to really get some flavor into the meat. And then I sprinkle a bit into the shoe.


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[Assistant] The chicken, come on with those spices, yes! I've got zero


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[Assistant] Can I have cooked, er, Rochelle Moll? With braising liquid on this side as well.


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[Assistant] Where he's made this as good as it is, is in that liquor there. It's a great dish for this challenge, because it heroes the chicken.


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[Assistant] It was glossy, had a good sheen on it from that sauce. That rice, really rich and beautiful.


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[Assistant] Let's, uh, let's talk about the elephant in the room, that being the egg.


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[Assistant] The flavour of this was as enchanting as the aroma. The biggest credit to her for not losing it.


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[Assistant] Is that all lemon though? Yeah, I just ate it. Oh. It's 100% lemon though.


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[Assistant] And I went in for the chicken first and that's all I could taste. Like, it blew my palate out of the water. He's just overpowered the chicken.


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[Assistant] We've ended up with this just onslaught of Len and Meryl in not a great way. And again, it could have been.


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[Assistant] And that's why, unfortunately mate, you're the first person eliminated from My Chef 2021.


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[Assistant] I just want to keep learning and keep growing and really figure myself out as a person.


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[Assistant] I just wanna stick my face in the bowl. Oh my god.


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[Assistant] It represented egg, fantastically well because of the meringue, but how the dish ate.


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[Assistant] On your chicken, expertly cooked. Your chum's fantastic. Your bread was really good as well.


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[Assistant] It's everything that I love about chicken on a barbecue, mate. So, great cooking.


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[Assistant] Round one was simple. You have to feature either chicken or egg.


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[Assistant] Which is the ingredient you didn't use in round one. So, for Yo-Yo, Amir, Dan, Trent, that's chicken. And Linda?


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[Assistant] Good morning everyone! Now today's guest...


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[Assistant] Being a team leader on MasterChef, it's a bucket list thing to do. And for an Otolingki challenge, yes please.


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[Assistant] I've got the brown, I've got the ginger. I'm on the brown team today. I've self nominated as team leader. Looks like we might have to miss four. I'm thinking, what would I blame you two? Spring onion over there in that basket. So, flavor is at the forefront of my mind. Okay, talk to me about this entree.


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[Assistant] I'm just hoping that the dumplings are cooked through. I don't want to find my team in tomorrow's elimination. Guys, the flavours are good. The flavours are good.


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[Assistant] So our entree is a pork and mushroom potsticker dumpling with a Szechuan numbing oil dressing.


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[Assistant] For main we have pumpkin that's roasted with the fenugreek marinade and a curry sauce. We also have a baked tomato rice. And finally we have our peanut chipotle ice cream sandwiches.


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[Assistant] Filled to the same capacity, dumplings sitting on a plate. I would be really happy to be served that anytime.


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[Assistant] It was dry, it was squeaky, it didn't really need to be there in terms of a neutralizing, grounding kind of flavor.


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[Assistant] All of that goodness in the bottom, gosh it would have been such a wasted opportunity to not do something with it and I'm glad that you did the right thing with it.


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[Assistant] Great team, do not be disheartened. Take what you can from today's course and remember whatever lessons you learn and just keep them with you as you move forward.


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[Assistant] What cuisine have we got? Middle East. Middle East should be vegetables. Let's do other things. All vegetables? Yeah. All of us agree that it needs to be vegetable focused. Yodham's on our screen cooking with us today. I feel like he'd be proud of us to be pure vegetables.


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[Assistant] Uhm, and that's just gonna be done with a tahini caramel. Okay. Uhm, and I think this should be another element, but I'm not there yet on that. And we have, uh, Winona with the peanuts on dessert. We've got a peanut ice cream with a salted caramel.


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[Assistant] Engineering has given a lot to the world. It's transformed the nature of work, improved sanitation, and helped create vital infrastructure. The bad news is that to power the tools and processes behind those developments, we've relied on non-renewable fuels.


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[Assistant] ...known collectively as fossil fuels. It's been terrible for the atmosphere and oceans, and is changing our climate in dangerous ways. Whether we like it or not, we're going to have to find new ways to power our world.


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[Assistant] Despite their terrible effects on the environment and limited supply, for now, non-renewables do a really good job of meeting our energy needs. In 2017, 80% of the power used in the United States was supplied using fossil fuels.


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[Assistant] The process of splitting atoms, which releases far less CO2. Unfortunately, fission produces radioactive waste and also relies on non-renewable fuel sources, such as uranium and plutonium. All of these methods operate on broadly the same principle, essentially operating as a heat engine. A working fluid, often water, is heated by the fuel to expand and do work.


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[Assistant] So what about the remaining 11% of power? That came from renewable energy sources, the kind that are generated about as fast as we use them. Some of the major renewable energy sources come from processes that are naturally occurring on Earth.


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[Assistant] Wind power, solar power, hydropower, which is based on flowing water, and geothermal power, which uses the heat of the Earth deep underground. None of these sources are things we'll run out of. We have a good few billion years left of sunlight, for example. And what's more, renewable energy tends to release fewer harmful byproducts, like carbon dioxide.


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[Assistant] Take hydropower, for example, which converts the kinetic energy from the motion of running water.


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[Assistant] To turn the turbines of a generator. That works well in some places, but the problem with this approach is that it's tricky to control the generation of energy to meet demand. You don't want to put lots of power into the grid when it won't get used, and you want to be able to ramp up the supply when the demand suddenly spikes. Like during the halftime break when the English football team, that's soccer to you Americans, played Colombia in the 2018 World Cup.


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[Assistant] A huge number of people in the UK open their refrigerators to grab a drink or a snack.


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[Assistant] The total increase in demand was measured to be 1200 megawatts. That's an extra demand for power equivalent to several power plants. With fossil fuels, you can control the amount of fuel being burned, and therefore the amount of power being produced. Run-of-river power plants struggle with this because the amount of power they generate depends on the flow of the river, which in turn,


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[Assistant] If you install an intake valve that opens or shuts to control the water flow through it, you can even manage the production of energy to meet the changing demands of the electrical grid. Unfortunately, flooding an area with water isn't consequence-free.


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[Assistant] Changing the environment so suddenly and preventing the natural flow of water downstream can have devastating consequences for the local ecology. There's also the risk of the dam breaking if it was built improperly. Despite those challenges, hydropower has been enormously helpful.


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[Assistant] While also allowing the wind to efficiently rotate them to power the generator. It's as complicated as designing an airplane wing. Once again, you run into the problem of demand. You can't control the strength of the wind to increase or decrease power generation as you need it. Even if that were possible, you'd still have to transport it from the sparsely populated open plains where the wind blows more easily.


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[Assistant] As the collection of turbines is known, should be built. So wind power has only generated 4% of the world's total power supply in recent years. Location also plays an important role in another renewable energy source.


[User] Please transcribe this text

[Assistant] Normally near the Earth's tectonic plate boundaries, to use them as a heat source for a power plant. Then, all you need is to pump water to that location and create another channel for steam to rise through to do work on the turbines. The biggest problem comes with setting up a geothermal power plant in the first place. It can be expensive to drill and explore for underground conditions that are exactly right.


[User] Please transcribe this text

[Assistant] Solar energy. In fact, the amount of sunlight the Earth receives in just a single year is twice the total amount of energy that will ever be extracted from fossil fuels.


[User] Please transcribe this text

[Assistant] And the uranium used in nuclear fission combined. The challenge is finding efficient ways to harness that energy, because turning sunlight into electricity isn't simple. The most promising technology we have is called the photovoltaic, or simply, PV cell. Most people know them by the name given to many cells arranged together.


[User] Please transcribe this text

[Assistant] Unlike everything else we've looked at, there's no trace of a turbine here. Instead, as we saw when looking at semiconductors, solar panels use two different semiconducting pieces to set up an electrical field.