Hot air swells and rises

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Q1: Which way does warm air go – up, down or does it just spread out in all directions?

[Answer]

When a gas is warmed, it swells up a little and so gets lighter. Once it has become lighter than its surroundings it rises.

This is why the gases (and smoke) from a fire go up the chimney and do not spread out into the room. It is also why hot air balloons rise. Bubbling clouds are also made of air that is slightly warmer than their surroundings.