Why does hot air rise?

[scilearner]

Hello everyone,

 

I know the pressure at bottom of atmosphere is higher than above. Then when I suddenly heat up air at the bottom of atmosphere why does it rise? Ok if it is buoyancy, why doesn't the air at the top fall down towards earth, because they are less dense so they must fall right? I can understand how a small leaf can float in air but how can the medium itself float up? Thanks

[ewmon]

Heat, or thermal energy, refers to the kinetic energy (½mv²) of molecules, which constantly vibrate.

 

"Hotter" means more velocity, which means more pressure (imagine people in a crowd pushing and shoving each other more), which tends to create expansion, and thus, lower density. Buoyancy causes the heated molecules to rise. This occurs singularly as mushroom clouds caused by detonating nuclear weapons, lighting a match, etc. A constant stream of hotter, lighter gases occurs with candles, home radiators, chimneys, the earth's tropical regions, etc.

 

The less dense air at the top does not fall down exactly because it is less dense (just as a box of cereal has the more dense cereal at the bottom and the less dense air space on top).

 

...

[Mr Skeptic]

Buoyancy makes things that are less dense float over things that are more dense. A cloud of warm air has lower density at the same pressure. It will rise and expand, it will be even less dense than the surrounding air, so it can rise and expand more, higher than air that had previously been less dense -- so long as it remains warm.