Elementary Particle for Heat?

[Alex K]

Heat in the sense physicists use it is nothing but energy that is randomly distributed in a material or collection of particles. If you have a gas, the heat it contains is just the random motions of all of its molecules.

I like this explanation. Heat usually gets explained as the kinetic energy of all the particles. Although this explanation isn't quite right (I forget what the more sophisticated definition is), it gives pretty good intuition. As you remove particles your gas gets colder... etc.

Yes, but the random part is important. If you throw a ball, you would not count the resulting kinetic energy as heat because all atoms have the same direction. But if it hits some obstacles and bounces around till it is at rest, what happened is that this kinetic energy was distributed randomly among the atoms during the inelastic collisions it experienced, and the ball now rests but is warmer.