Why do highly pressurized cans/gas cylinders ( like eg. lighter gas, propane cylinders etc) go cold when the pressure is released?
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It’s a [basic (physics) law of gases](https://en.wikipedia.org/wiki/Ideal_gas_law) that pressure, volume, and temperature are related. P * V / T = constant.
It’s because [when you look at atoms and molecules of a gas](https://www.youtube.com/watch?v=WhP6zJbSxec), you can think of them as a bunch of tennis balls bouncing around wildly. The pressure is the force they apply as they bounce off the walls of the can, the volume is the space they bounce in, and the temperature is the energy with which they bounce.
In any case, a pressurized cylinder has a fixed volume, the gas can’t inflate it like a balloon. So the relationship above, P * V / T = constant, becomes P * constant / T = constant, or P / T = constant. You decrease the pressure (by letting gas out), and the temperature decreases so that the ratio P / T stays constant.
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