Compressed gas

Notwithstanding my incredible feelings of loss with the Shuttle Columbia Crew, my question may seem trivial, but here goes. The news and experts continue to report friction causes the heat underneath the shuttle. Doesn't friction have a small part to do with the heat as opposed to the compression of gas?

thanks

 

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Compression of Gass

The compression of gas causes a great deal of the heat on the bottom of the shuttle. But friction is the larger part, because without friction, there would be no compression. It would be a very difficult calculation to isolate compression in this scenerio, involving even the shape and texture of the surface. Still, without friction, no compression.

 

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The compression would take place regardless of how much friction was on the surface. Friction will just move the compression location by slowing down the air and causing turbulence.
Now the compression itself causes VERY little heat transfer to the shuttle. (This can be done simply by using a FEA program and setting friction=0.) However the amount of friction increases because the compressed gas is denser, so more gas molecules hit the ship per second. This friction generates the heat.

Friction is defined as the force cause by a shear motion, so compression is possible without friction.

SIMPLE EXAMPLE
Put your hands together lightly and rub them together. They heat up. Press your hands together and they heat up more. The heat given off by friction is related to the pressure.

Now grease up your hands with something (no questions asked

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). Repeat the experiment above and (if the lubrication is good enough) you will have very little heat generated.

 

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The MAIN cause of heat to any object during re-entry will be due to the compression/pressure of the air...it is a mis-conception that friction generates the heat...

(A bicycle pump is a good example of the amount of heat that can be made in the adaptor/nozzle )

 

Thanks blo

Seemed that pressure made more sense, but everyone has always said friction. Great analogy too.

thanks again