when things burn, water in them and water vapour in the air get hot and form a kind of cloud. Mixed into it are bits of things that didn't burn in the fire. Together they make smoke. In a fire, the heated air sweeps water vapour, bits of the fuel that failed to burn and other matter up into the air. The vapour itself is invisible, but if it cools then it can be seen as droplets. These come together with other droplets and the bits and make smoke. When a fire burns well even soot is consumed, so there is very little smoke. That's why a pan's bottom won't turn as black over a blue flame as it will over yellow flame. Fires make a lot of smoke only when they don't burn well. The water and the little unburned spedks in smoke spread out and drift away in the air. Bigger specks fall back to the ground.
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