Why does water boil?
For grown-ups: the science
Water boils when heat turns some of it into water vapor bubbles that rise and pop.
Heating raises the kinetic energy of water molecules. At the boiling point, water vapor can form stable bubbles throughout the liquid; these rise and burst at the surface. The boiling temperature depends on air pressure.
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Transcript
A pot of water is getting warm on the stove. Why do bubbles suddenly pop up?
Heat moves from the stove into the water. The water’s tiny pieces begin moving faster.
Deep in the pot, some water turns into water vapor, a gas. It makes bubbles that float up.
At the top, the bubbles pop and the vapor mixes with the air. That bubbling is called boiling.
So water boils when heat helps it turn into water vapor all through the pot.