Heat is nothing but molecular movement, the violent oscillation of the particles of a body.

When you apply the brakes to the train, the train stops.

But what has become of its motion?
It turns into heat and makes the brakes hot.

Why do people grease the axles?
To hinder them from getting too hot, which they assuredly would become if friction was allowed to obstruct the motion.
You understand, don't you ?" "Don't I though ?" replied Ardan, apparently in earnest.

"Let me show you how thoroughly.