Why does "heat" rise?

Question

Please provide a scientific answer in specific detail. This is just for my own curiosity... so I am looking for an in depth physics/mathematical explanation as to why heat rises above cold air?

What makes the air "more dense"? Translation: What causes some air molecules to be more dense than others?

Answer 1

Air does not rise or sink because it is hotter or colder than the surrounding air. It sinks because it is denser and rises because it is less dense.

If you heat a parcel of air, by volume it is less dense than the same air unheated but this is not the only thing affecting the density of the air. Gravity holds the atmosphere to the planet and pulls air molecules closer to the ground so, regardless of temperature, air is denser close to the ground than it is higher up.

The temperature of the air decreases as you get higher in the troposphere. If warm air rose and cold air sank, this situation would be impossible. It is possible because the warm air near the ground is denser than the cold air above it. If the air near the ground is heated further so that it becomes less dense that the air above it, it will rise - and this is what happens to form convective cloud.

The simple thing to remember, though, is that air doesn't rise just because it is warm, it rises because it is less dense than the air above it. The denser air sinks and forces the less dense air to rise.

Answer 2

Heat doesn’t rise.
Heat is a form of energy. Air molecules absorb radiation and move faster. The faster they move, the more space they occupy. Since mass is the same, but volume is greater, a cubic unit of hot air will weight less. In other words, there are less molecules in that volume. That’s the concept of density: mass per unit of volume.
Heavier air (that is, colder, more dense air) will fall, as any weight does, in order to restore pressure equilibrium.
This is is the same as popcorn in a bowl. Before heating it in a microwave oven, you have x cubic units of corn. After microwave radiation, volume has expanded. It’s the same amount of pop, though. And if you look closer, there are still some grains that didn´t pop. Those went to the bottom of the bowl (for other reasons, yes, this is an analogy).
That´s the physical explanation of air movement. But, heat doesn’t rise. Heated air does. Lower density air.

Answer 3

Heat in and of itself does not move. But you are probably referring to warm air, so here it goes!

The ideal gas law:
PV = nRT
where P is pressure, V is volume, and T is temperature. n and R are constant

So if you increase the temperature, but your air parcel ("box" of air) is at the same location (pressure), you must increase the volume to satisfy the ideal gas law.
When you increase the volume, the same amount of molecules are in this air parcel, but they have more room to move around. Since there are less molecules per unit area, your air is considered less dense.
Less dense air rises above more dense air because gravity has a stronger hold on the denser air (it weighs more).

Warm air can sink and cold air rise, however. This is called a thermally indirect circulation and is the result of larger scale forcings moving the air, rather than just temperature changes.

Answer 4

the molecules in cold air do not move fast so they stay closer together and the molecules in warm air move faster so they need more space and are hence farther apart. This along with moisture content afects the density. colder air is more moist therefore more dense, where hot air is dryer and hense less dense. The less dense air (hot air) will then rise above the more dense air (cold air).

Answer 5

heat rises above cold air as the density of the cold air is more so it sinks down and as the density of hot air is less it rises.

Answer 6

heat rises because it's less dense than cold air; in other words, it is lighter than cold air

Answer 7

Actually there is a method known as thermodynamics in which a higher temperature will always migrate towards a cooler temperature : with heat ---- heat will always migrate towards a lower temperature

Answer 8

because the warmer air molecules need more "room" to bounce around, the colder ones stay more still. The warmer ones bounce up wanting more room. thats the basics.

Answer 9

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