|MadSci Network: Physics|
when any substance is heated up it vibrates(as total energy e=e1+e2+e3+e4 where e3 and e4 are kinetic and potential energies of vibration.) and executes a SHM which implies that there is a source of force at the mean position of vibration but as far as i know there isn't anything there which can pull the molecule which is moving away from the mean position back towards the mean position.
Re: what applies force from the mean position of a vibrating molecule?
Try the links in the MadSci Library for more information on Physics.