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I have some small problems with understanding increased tempature due to adiabatic prosesses. For instance, if you have a pump and pump air into a tire, the tempature within the pump will rise. This happends because you preform work on the gass in order to compress it. But when you retract the handle back to it's start position, the volume will increase and the tempature will decrease. So how can the tempature net increase in this process, when you retrackt the handle equal amounts of times as you push it. Lest say we use equal amount of force both ways.

Another questions I have is; why does retreacting the handle decrease the internal energy of the gas? In this process, its your hand that does the work for the most part, and not the gas. So the gas wouldnt really transfer alot of energy (work).

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    $\begingroup$ There is a check valve in the pump that doesn't allow the air to expand back out again. There is also a second check valve in the pump that allows outside air to enter the pump during the backstroke, but which closes during the downstroke. $\endgroup$ – Chet Miller Feb 9 '17 at 14:55
  • $\begingroup$ Also don't forget friction. $\endgroup$ – Deep Feb 10 '17 at 5:38
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Imagine you can shut off the flow of air through the pump, so the same air stays in there all the time. When you push the handle, you compress the air, and it gets warmer. You can't push it very far, because the air pushes back hard. If you let go of the handle, it will pop back out. The compressed air does work on the handle, and it cools back to approximately its original temperature. As Deep pointed out, friction will gradually warm the pump if you do this many times. In other words, retracting the handle decreases the energy only if there's still compressed air in the pump, in which case the air retracts it for you.

When you pump air into a tire, the tire gets warmer, because that's where the compressed air goes. When you pull the handle out, you're not decompressing the air significantly; you're just making room for new air to come in. The new air is at the ambient temperature and pressure until you push the handle again. The pump gradually gets warmer, partly because of friction and partly because of the compressed air that's on its way to the tire. It doesn't cool because there's no decompression. There can't be an equal amount of force on the handle both ways, because compressing air into the tire always requires more force than letting new air in.

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