Twisting a plastic water bottle transforms its volume, pressure, and also temperature—and also ends through a bang.

You are watching: How to pop the cap off a water bottle

Caution: This Snack involves flying bottle caps. Use eye security and aim safely ameans from yourself or anyone adjacent.



One half-liter (500 ml) clear, thin-walled plastic water bottle via screw-on cap(bottles via thin, transparent caps job-related best)GogglesOptional: isopropyl alcohol, hand-held infrared thermometer, a partner

Note: If your water bottle happens to be complete of water, drink up to empty it. It’s fine—also preferable—if tright here are still a few dropallows of water left inside.

Placed on your goggles.

Screw the cap on the bottle, yet not all the way: The cap have to be tight sufficient to make an airtight seal, but loose sufficient so you have the right to unscrew it through a flick of your thumb. (You’ll figure this out after one or two tries.)

Grab the bottle at both ends and also twist your hands in opposite directions. Twist hard—difficult sufficient to create a narrow “waist” about the middle of the bottle. (Click to enbig photos listed below.) Do you notice the bottle feeling warmer as you carry out this?


Point the height of the bottle away from yourself or anyone surrounding. While holding stress and anxiety on the twisted bottle, remove the cap through a sideways flick of your thumb. Caution: The cap will certainly fly off swiftly. Never before aim it at another person.

Watch carefully: You might see a tiny cloud of mist form near the mouth of the bottle after you release the cap.Note: If you can’t gain mist to arise from the mouth of the bottle, try including a few drops of isopropyl alcohol, and then shake the bottle. Isopropyl alcohol’s reduced vapor push will condense even more easily than water vapor as soon as you unscrew the cap.

If you occur to have an infrared thermometer, repeat the experiment and also have actually a partner measure the temperature of the bottle prior to you squeeze it, as it is being squeezed, and also then after the cap hasbeen released. (Click photo to enbig.)


If you want to carry out this Snack aget, just blow right into the bottle to re-inflate it and also you"ll be prepared to go.The bottle deserve to be provided multiple times. Note: Do notre-inflate by mouth if you"ve previously provided isopropyl alcohol in the bottle.

Did the cap go flying off? Did you hear a “pop”? Did you see mist wafting from the mouth of the bottle? All of these events tell you that your “empty” bottle was anypoint yet empty.

When you twist the sealed bottle, you decrease the volume of the air trapped inside. When gas molecules are compelled closer together in this way, the press inside the bottle rises. This raised push is what renders the cap fly across the room once released.

The “pop” you hear is led to by a sudden adjust in air pressure. When you release the cap, the higher-press air inside the bottle rushes out right into the lower-pressure air inside the room. This sudden growth creates a press wave that you hear as sound.

As you twist the bottle, you might feel (or measure) it obtaining warmer. After the cap flies, you might noticethe bottle obtaining cooler. Tbelow is a straight connection in between press and temperature in a gas:increasing the push rises the temperature; reducing the push reduces the temperature.

The mist that creates reveals that there’s not just air inside your bottle, but also some water vapor. At the reasonably greater temperatures and also pressures insidethe twisted bottle, the water vapor continues to be a gas. But as soon as you release the cap, the sudden drop in pressure and also temperature reasons the water to condense right into visible droplets of liquid water.

Tright here are numerous various other experiments and design difficulties you can execute through this Snack. For instance, you could desire to investigate how far your cap will fly. Is tbelow a relationship in between the number of twists and also the distance at which the cap lands?

How much does the press adjust as soon as you twist the bottle? Can you engineer a mechanism to identify the inner pressure of the bottle prior to and also after twisting?

How much does the volume change? Can you number this out using graduated cylinders, measuring cups, or various other tools?

Can you usage the measurements from the tasks over to come up via a connection between temperature, pressure, and volume? This connection is well-known as the best gas law.

As a homework assignment, ask students to lug in empty plastic water bottles. Take students exterior or right into a gym. With no arrival and also with a twist of the wrist and also a flick of the thumb popthe optimal off a bottle. This is an exciting means to introduce this Snack through a bang!

Let students connect in this activity after a quick demonstration (includinga discussion of proper safety precautions). Note: Because you have the right to re-inflate your bottle by mouth, each experimenter need to have actually their very own bottle. Do not re-inflate by mouth if you"ve formerly provided isopropyl alcohol in the bottle. Depending on the number of students affiliated a even more security precaution would be to label each bottle and also cap so students deserve to retrieve their own linked part.

After students have actually had a possibility to launch their bottle caps, ask them what they desire to perform or attempt following.This Snack can bring about an explosion of investigations and also inquiries relating directly relate to core clinical ideas andScience and Engineering Practices. Many kind of questions or self-enforced difficulties might aincrease such as: How have the right to I make my cap go further? Who deserve to make the most clouds in their bottle? Who have the right to make the loudest pop? Have students take notes and also make measurements; encourage them to compose dvery own their concerns and style experiments to investigate better.

See more: Can You Take A Convertible Through A Car Wash, How To Wash Soft Top Convertibles

This Snack needs no background expertise, simply a strong wrist and rapid thumb. However before, this Snack have the right to cause discussions and lessons on a range of gas-legislations and kinematic concepts. It deserve to expose useful applications of this sensations in modern machines—choose combustion engines, refrigerators, and rockets—and also the research of the weather (meteorology).