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Originally Posted by Who
Quibble Mode [On]
This is officially quibbling but I feel that it is important to always keep in mind, especially on a site like this.
Warmer air (or water) rises, but heat itself travels in whichever direction it can to get to something that has the least amount of heat.
Heat can move through conduction, radiation and convection. With conduction and radiation heat travels the easiest path regardless of direction.
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So what happens when things heat up?
They become less dense. Less density compared to the surrounding material, in fluid dynamics, suggests that the less dense material should move upward on a measurement scale.
If heat radiates into something else, all things equal, the overall effect will still be heat rising.
According to physics, all things will take the path with the least resistance. This is a given. This is also why, when you want to keep heat in your house, you insulate the
ceiling, not the floors. This makes it more difficult for heat to
rise directly out of your home, and into the airfield surrounding your home. This, however, does not prevent the physical net effect of heat rising, for after it radiates through the walls, (the next apparent "easy" path), it will still rise into the atmosphere until there isn't sufficient energy to keep it heated beyond the temperature (and thus, less dense than the surrounding) fluid. This means that as it's rising further away from a heat source, which keeps the heat energized, the heat dissipates, cools, and returns to the heat source. This is what causes convection currents.
Once again, the net effect is still that heat rises and cold sinks.