Can Heat Flow from Cold to Hot?

[NicholasB54]

If heat flow is the momentum change from a faster moving atom or molecule to a slower moving one, and momentum is mass x velocity is it possible - for a very limited amount - for heat to flow from a slower (colder) heavy atom to a faster moving (hotter) atom ?

 

[Philip Wood]

(1) It's energy transfer, not momentum transfer, that's relevant.

(2) It is, I believe, possible in an oblique collision for a faster molecule to pick up speed (and hence KE) from a slower molecule of the same mass.

(3) But we wouldn't classify this as a flow of heat. To constitute a flow of heat we'd need a net transfer of energy for many molecules.

 

[NicholasB54]

I was confusing energy change and momentum change alright

Thanks Philip