If you want to know how heat moves around, you need to understand thermodynamics. The theory is governed by three laws. The first one states that whatever is going on, the total energy in the Universe stays the same. In other words, you cannot create or destroy energy; you can only change one form of energy into another. The second law says that an isolated system's entropy always increases. Entropy is a measure of the part of its energy that cannot be put to work in some way.For example, as a watch spring unwinds, it has less and less power to keep the watch running. Its entropy rises because the spring's potential energy is slowly transferred to the hands as kinetic energy, with some energy also lost as heat because of friction in the mechanism.
The third law says that, as a system's temperature drops toward absolute zero (the lowest possible temperature: -459.67°F; -273.15°C), all natural processes cease to occur, and the entropy reaches a minimum. The upshot of this is that it is impossible to reach absolute zero because no processes can get you there.Thermodynamics is not as abstract and esoteric as it sounds. It was developed in the 19th century by William Thomson, (knighted) Lord Kelvin, and forms the basis for your house's refrigerator and central heating, the engines that move your car, and the biological processes that keep you alive.
by Michael Brooks, 30 Second Theory