The nicest way is to use a Google account [free] , and upload your photos to Google+. If you use the standard filesize, all pix are free to store. Then use the Google+ Slideshow Feature, as you use the Google Cast Extension casting function.
Explain that water is made up of tiny particles, called molecules, which are too small to see. These particles are always moving, even in very cold water. Since water molecules move, the molecules help mix the food coloring. However, the color mixed faster in the hot water than it did in the cold.
The real-world explanation of water density is actually more complicated, as the density of water also varies with the amount of material that is dissolved in it. Water in nature contains minerals, gasses, salts, and even pesticides and bacteria, some of which are dissolved.