Are thermal forces defined?

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Offline Richard777

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Are thermal forces defined?
« on: 11/04/2016 19:27:11 »
Are thermal forces valid?
How are they defined?


Offline evan_au

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Re: Are thermal forces defined?
« Reply #1 on: 11/04/2016 22:00:25 »
When you change the temperature of a gas, the pressure (force) also changes.

This effect is very important in the study of thermodynamics and heat engines.

The same is true for liquids and solids, but the relationships are not so easy to calculate as it is for a gas. So bridges have "expansion joints" to allow for the bridge to safely move as it heats up and cools down on a daily basis.

Thermal radiation can produce a small pressure, due to the momentum of infra-red photons. But this force is so small that it is effectively undetectable on the surface of the Earth, when we are surrounded by air, which forms convection currents near heated objects.

This effect did cause a slight deviation in the path of the Pioneer spacecraft, see:

Or are you thinking of some different form of thermal force?