Kinetic molecular theory: particles always on the move

0:00What are solids, liquids and gases really made of?

0:05Kinetic molecular theory says that all matter is made of tiny particles, far too small to see.

0:12The word kinetic means to do with motion, and these particles are always moving.

0:20In a solid, the particles are packed close together and vibrate in place.

0:26So the particles in a solid do move. Each one just stays in its own place.

0:34In a liquid, the particles are still close together, but they can slide past each other.

0:40In a gas, the particles move fast and are far apart, spreading out to fill their container.

0:47In every state there are spaces between the particles. They are small in solids and liquids, and large in gases.

0:56The energy of motion is called kinetic energy. The faster a particle moves, the more kinetic energy it has.

1:04The particles move at different speeds, so temperature measures their average kinetic energy.

1:11When we add energy, for example by heating, the particles move faster and the temperature rises.

1:19Heating does not make the particles bigger. When most solids are heated, they expand because the spaces between their particles grow.

1:29So all matter is made of particles that are always moving, with spaces between them, and adding energy makes them move faster.