Book 3, Question 44
Why Does Steam Rise?
Steam is water that has turned into a gas. Heat makes water molecules fly apart, so hot steam is lighter than the cool air around it. And lighter stuff floats up, like a bubble!
From the book
Page from A Million Whys Book 3
More fun facts
- Real steam, or water vapor, is invisible. The white cloud you see is made of tiny drops of liquid water.
- Those tiny drops form when warm, wet air above the water cools down.
- That is why a bath or a cup of tea gives off more visible steam on a cold morning than on a hot afternoon.
- In Hawaii, warm air leaking from the ground can turn into visible steam on cool mornings.
- Steam sometimes rises from the ground before lava comes out, because rising magma heats the groundwater.
- In space, NASA's Webb telescope saw what looks like steam rising from cosmic mountains. It is really hot gas and dust streaming away from a cloud where stars are born.
Sources: Scientific American, U.S. Geological Survey, NASA Science
Questions kids ask
Why can I see my tea steam more in winter?
Cold air cools the warm vapor above your cup faster, so more of it turns into tiny water drops you can see.