Kara Orndorff, age 8, of Waukomis, Oklahoma, for her question:

What are the bubbles in boiling water?

Water is made of tiny molecules that are much too small for our eyes to see. These water molecules are frisky midgets and what they do depends on how warm or how cold they are. In ordinary weather, they cling together in slippery, slithery strings. These strings also are too small to be seen. But when zillions of them cling together, they form a drop of liquid water. And that we can see. When the weather drops to freezing, water molecules slow down and come to a stop. Then they fit themselves together to form a solid chunk of ice.

The molecules in liquid water are just warm enough to cling together and slither around in a runny liquid. When you set a kettle of water on a hot stove, its molecules move faster and faster. When it gets hot enough, some of the molecules separate one by one. The separated molecules change from liquid water to water gas. When the water gets hot enough to boil, the gas collects in bubbles. The gases are lighter than liquid water, so up they float to the top. There they sail off and mingle with the other gases of the air.