Why does temperature rise with pressure?

[spacetime]

If you apply force to a liquid, wishing to compress it, but it is incompressible, then no work is done on the liquid. No energy is provided to the liquid.

But you have certainly lost some energy, it has gone into your metabolic processes and has been released into the atmosphere. Basically, it has been wasted.


spacetime
www.geocities.com/physics_all/index.html

 

[DreadPR]

Jumping into this a couple years late :)

I find it hard to accept that the increase in temperature is only because of a moving surface. The argument seems to be that just like a tennis ball, the molecules bounce off the moving surface (tennis raquet) and increase their speed.

The problem I have is that the speed of the molecules is so much faster than the speed of the surface. It seems to me that the increase in speed that the moving surface imparts would have a very small increase in the temperature. It almost seems like it would be a negligible increase ... 0.00something percent. But as we know the temperature rises quite appreciably.

Consider a propane container used for your standard BBQ grill. As you use the propane with your grill turned on, the container gets very cold. What is happening here? The number of molecules in the container are decreasing. But the walls of the container are not moving? How then are the molecules moving slower if they are not striking a backwards moving surface (as was previously argued). There has to be some component to the change in temperature added by the fact that distances between molecules changes with changing pressure.

 

[Mapes]

I find it hard to accept that the increase in temperature is only because of a moving surface. The argument seems to be that just like a tennis ball, the molecules bounce off the moving surface (tennis raquet) and increase their speed.

The problem I have is that the speed of the molecules is so much faster than the speed of the surface. It seems to me that the increase in speed that the moving surface imparts would have a very small increase in the temperature. It almost seems like it would be a negligible increase ... 0.00something percent. But as we know the temperature rises quite appreciably.

Hi DreadPR, welcome to PF. Yep, this thread is five years old, and some of the original players are no longer active. The moderators may move it to a new thread if they desire.

You need to consider that the same molecule gets many, many momentum-increasing "kicks" as the surface moves inward. (Alternatively, you could calculate how fast the surface would have to move to give an arbitrary molecule just one kick. You'll find it's comparable to the molecular speed.)

Consider a propane container used for your standard BBQ grill. As you use the propane with your grill turned on, the container gets very cold. What is happening here? The number of molecules in the container are decreasing. But the walls of the container are not moving? How then are the molecules moving slower if they are not striking a backwards moving surface (as was previously argued). There has to be some component to the change in temperature added by the fact that distances between molecules changes with changing pressure.

The gas inside the container is doing work on the gas that leaves the container, and thus its temperature decreases, also decreasing the container temperature.

 

[DreadPR]

You need to consider that the same molecule gets many, many momentum-increasing "kicks" as the surface moves inward. (Alternatively, you could calculate how fast the surface would have to move to give an arbitrary molecule just one kick. You'll find it's comparable to the molecular speed.)

Thanks for the welcome and the quick response :)

Yes I didn't consider that there would be many many kicks.