The amount of movement within a substance:

Question

Quizplus · Accepted Answer

All matter is made up of particles called atoms (which then make up molecules). Atoms and molecules are always in motion, bumping into each other or vibrating back and forth. Heat, a form of energy, is created from the motion of these particles.
The particles in solids are tightly packed and can only vibrate. The particles in liquids also vibrate but are able to move around by rolling over each other and sliding around. In gases, the particles move freely with rapid, random motion.

The Amount of Movement Within a Substance