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Why does hot air rise and cold air sink?

Let us think about why some things sink and some things float in water. A thing will float if it ways less than the water it displaces. Let us imagine you have a slice of white bread. If you put in water, it will float. Now take another slice of white bread and SQUEEZE it into a tiny little dough ball. Put that ball in water and it sinks. It is the same amount of bread - it ways the same - but it is denser. Now back to your question. When you heat air, it expands. When you cool air, it "shrinks" (like the bread being SQUEEZED). The hot air is less dense than the cold air, so it floats - or rises above the co air.

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