eli5: Why does air-in-a-can get cold when you use it?
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As gases increase in temperature they become less dense. The molecules are moving around at a higher speed, this is due to the extra energy.
So as a gas is compressed it loses this energy, which is partly why compressors get very hot. That energy has to go somewhere. The gas eventually loses enough energy to become a liquid. Most compressed gases like duster, and propane for example are in liquid form within the tank.
When the gas is released it expands and robs thermal energy from anything it touches.
Meanwhile the remaining liquid in the can can expand slightly because there is less pressure in the can. Some of the liquid spontaneously boils and becomes gas to fill in the extra space. This allows it to absorb more energy. That energy comes from the metal of the can and surrounding air, causing the can to get cold.
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