Kinetic Theory All matter is made up of particles, called molecules. They are constantly in motion. When they are close together, the molecules attract each other strongly. When they are far apart, they hardly attract each other.

Solids The particles are close together. They are held together by strong forces. They vibrate to and fro, but cannot change positions. They have a fixed volume and shape.

Liquid The particles are close together. They vibrate so vigorously that the forces can no longer hold them in fixed position. They have a fixed volume but no fixed shape.

Gas The particles are very far apart and hardly attract each other. They move at random at very high speeds. They have no fixed volume and shape.

Smoke particle

Smoke Particle

Brownian Motion A smoke particle is bombarded by millions of air molecules around it. The bombardment comes from all sides but not in equal number. Brownian motion provides evidence for particle motion. This can be explained by using the kinetic theory.

Smoke particle Air Particle

Smoke particle Air Particle

Brownian Motion

Ans: E

Ans: B 

Ans: E

Kinetic theory Model (3 Dimensional model)

Gas molecules Volume of Gas Pressure of Gas Temperature of Gas

Kinetic theory and Boyle’s Law When a gas is compressed, the molecules have less volume to move in. They hit the walls more often and so produce a greater pressure.

Kinetic theory and Charles’ Law As temperature rises, the molecules move faster and hit the walls more often. If the pressure is to remain constant, the volume must increase.

Kinetic theory and Pressure Law As temperature rises, the molecules move faster. When the volume is fixed, the molecules hit the walls more often. This increases the pressure.