Why does smoke travel upwards?

Andrew - It's interesting. Smoke is a generic term. It's a lot of hot gases and particles as well, mostly soot and tar. But of course, hot things, hot gases expand and become less dense than their surroundings. So a hot gas over a fire is sort of floating on the cooler air around it, so it will rise up.

Chris - I suppose the same could be true then of water going up in the air. So if you evaporate water from the sea and it goes up in the air as water vapour, and then it forms raindrops in clouds, it's being held aloft in clouds as water particles because there's rising warm air pushing it up from underneath. And there's enough rising warm air to do that. The smoke particles are small enough that they're going fast enough that it doesn't take much of a nudge to keep them up there. But the ball, much heavier, stays up for longer.