Does hot air rise or cold air sink?

You may be right. The force that they respond to is gravity. Cold air, being denser, will, in a fluid medium, be drawn closer to the earth, displacing warmer, less dense air.

Does Hot Air Rise

Both things happen together, the hot air rises and at the same time the cold air sinks. The cold air sinks as you say, because it is denser, and at the same time the hot air rises because it is less dense.

Gravity is behind this. Both the hot air and the cold are are gravitationally attracted to the earth. They fight for position, and since the cold air is denser, it wins and pushes warmer air out of the way. This is what causes buoancy. It's what floats your boat.

According to physics, heat is tranferred from the hoter medium to the colder medium. In this case, the heat is mainly transferred by convection to the colder medium (not conduction, because air is a poor conductor).

So hot air rises.

Well, we are talking about relative differences in densities here. Mix two fluids of difference densities (yes, gases are fluids), and the heavier fluid will sink through the lighter one. But in the case where the densities are the same at the same temperature, the warmer air expanses as it is heated, pushing aside the colder air above, and falling back through itself as the boundary is being cooled, setting up many eddying currents

Fluid dynamics are never easy.

Hot air rises - it is also not like that :)

Atmosphere is made up of layers - when the layers at the bottom of the hierarchy get heated up the heat from them is transferred to the layers above them via the process of conduction and that is how heat transfer takes place between the layers hence by the time the topmost layers get heated the bottom layer becomes cold as it had conveyed all its heat in upward direction. since we see that the bottom layers are cold while upper layers are hot we tend to say that hot air goes upward

Both phenomenon happen side by side. The high energy molecules of air creat a surrounding of high volume - forming less dense light area. this lower density region of hot gases cant hold the weight of cold-dense-heavy air and so the cold parts "fall down" by the action of gravity!!!!

you know this happens only on earth or gravitational bodies....noy in space - where there is no up , no down!!!!!

Hi >

See what you mean.

You could consider, that it as the same as water mass, etc.stuff with a higher molecular activity reduces it's mass volume ratio, so pushes colder stuff out of the way.

Conversely, stuff with a denser mass will "shove down" on warmer stuff coming the other way. Forcing it upwards.

So it is a bit of both, I suppose.

Bob.

If you put the cold air on top and warm air on the bottom the warm air will rise and the cold air will sink.

If you reverse the process nothing will happen!