why does cold air sink and hot air rise?

Answer 1

Cold air is more dense and therefore it sinks. Hot air is less dense so it floats.

Answer 2

It is very true that Hot air is less dense than Cold air. The reason why is because of the movement of molecules. Gases move very quickly and expand as they go, when they are hot the molecules move a bit faster, then they are cold the molecules like to stick around each other a lot more. It's kinda like how if you're hugging someone and they're sweaty you wanna get away from them but since you like them you'll stick kinda close by, and if it's cold out and the other person is warm so you keep close because you're cold.

That's a reason why cold air sinks and hot air rises.

Answer 3

It is wrong to say that cold air sinks and hot air rises because it doesn't. Denser air sinks replacing less dense air. very often cold air is denser than hot air so it sinks but that is because of the density, not the temperature.

If you go up in the atmosphere, in a balloon for instance, taking a thermometer with you, you will notice that the temperature falls as you rise higher in the troposphere. Cold air is overlying warmer air with the warmest air at ground level and the coldest at the tropopause. If hot air rose and cold air sank, you would expect the warm air near the ground to be replaced by the cold air above but this does not happen unless the air is forced to rise.

There is more air close to the ground than there is higher up so the air is denser there than it is higher up regardless of temperature. The hot air near the ground does not rise because it is denser than the cold air above it.

Air rises and falls because of the density not the temperature.

Answer 4

All of your answers so far are wrong. Hot air does indeed rise. Why does this happen? Well, its because the pressure in the atmosphere falls as you gain altitude (because there is less atmosphere over your head pushing down); the hot air is less dense than that around it, so this pressure gradient gives rise to a net force pushing up on the hot air. But as the hot air rises it experiences that lower pressure. And so it expands. From the gas laws you will know that if a constant mass of gas expands without any energy input it cools down. Utlimately it will cool down enough that it no longer rises. What this means is that air is naturally cooler the higher you go. The atmosphere is in a stable equilibrium when the change in temperature as you rise is exactly what is necessary to stop pocket of hot air rising. This is called the adiabatic lapse rate, and it is about 0.65 C per 100m. So if you go up a 1000m mountain the top is 6.5C cooler than the bottom. If you go up to 10,000m in a plane it is 65 C cooler (the outside of a plane is typically around -50C).

Answer 5

Let us think about why some things sink and some things float in water.
A thing will float if it ways less than the water it displaces. Let us
imagine you have a slice of white bread. If you put in water, it
will float. Now take another slice of white bread and SQUEEZE it into
a tiny little dough ball. Put that ball in water and it sinks. It is
the same amount of bread - it ways the same - but it is denser.
Now back to your question. When you heat air, it expands. When you
cool air, it "shrinks" (like the bread being SQUEEZED). The hot
air is less dense than the cold air, so it floats - or rises above the co
air.

Answer 6

The molecules in hot are moving more vigorous and randomly do make the hot air lighter or less dense. And for the cold air the molecules are moving more slower and is more closely pack making it more denser.

Answer 7

Air expands when it is heated, so there is less air in a given volume of hot air than the same volume of cold air, so the heavier (cold) air sinks effectively pushing up warmer (lighter/vol)
air.... in layman's terms!

Answer 8

Hot air doesn't rise. Cold air is denser and displaces (pushes up) the hot air.

Answer 9

Cold air is denser than room temperature air. Hot air is less dense.

Answer 10

Because hot air expands.