Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Richard777 on 11/04/2016 19:27:11

Title: Are thermal forces defined?
Post by: Richard777 on 11/04/2016 19:27:11

Are thermal forces valid?
How are they defined?

Title: Re: Are thermal forces defined?
Post by: evan_au on 11/04/2016 22:00:25

When you change the temperature of a gas, the pressure (force) also changes.
See: https://en.wikipedia.org/wiki/Combined_gas_law

This effect is very important in the study of thermodynamics and heat engines.
See: https://en.wikipedia.org/wiki/Heat_engine

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: https://en.wikipedia.org/wiki/Pioneer_anomaly

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