Why does heat rise?
(Lansing State Journal, April 24, 1996)


Because heat is not matter, it isn’t correct to say it rises or falls.  A better way to ask the question is: "Why do hot things (like hot air) rise above cold things (like cold air)?"

To answer this question, it is important to understand what heat is.

Heat is energy.  When we say something is hot, we really are saying it has a lot of stored energy.

What does this energy do?

Matter is made up of incredibly small pieces called atoms and molecules.  Atoms and molecules are always moving.

The more energy these atoms and molecules have, the faster they move.  The faster they mover, the more space they take up.

If something is hot, it weighs the same as if it were cold, but it just takes up more space.

This leads us to the concept of density.  Because hat air takes up more space than cold air, hot aur has a smaller density.

Less dense hot air will "float" above the more dense cold air.

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