Thermal Equilibrium
A hotter body has more thermal energy. Thermal energy is usually due to random vibrations of atoms. In a colder body, the atoms vibrate with smaller amplitudes.
When a hotter body touches a colder body, vibrating atoms of the hotter body collide with the atoms of the colder body. This increases the amount of vibrations in the colder body.
What happens when two bodies of the same temperatures are in contact?
Since neither is hotter nor colder, we would not expect any heat to flow. However, there are always random vibrations in the bodies, from their thermal energies. Some vibrations can be transmitted from one body to the other. Some vibrations can also be transmitted in the opposite direction.
This means that tiny amounts of heat would flow one way or the other. This could happen at different times, or at different points of the surface of contact, since the vibrations are random. However, on average, the net flow - the flow in one direction minus the flow in the opposite - is zero.
We say that the bodies are in thermal equilibrium.
Copyright 2010 by Kai Hock. All rights reserved.
Last updated: 13 October 2010.