The Kinetic Model (SQA National 5 Physics): Revision Note

The kinetic model

• The kinetic model is used in physics to explain the motion of particles

• The kinetic model is the idea that all matter is made up of particles that are always moving

• This model explains the properties of solids, liquids and gases

The kinetic model and gases

• Particles in a gas are in constant random motion at high speeds

• Random motion means that the molecules are travelling in no specific path and undergo sudden changes in their motion if they collide, either with:

  • the walls of its container

  • other particles

• Pressure in a gas is caused by the collisions of particles with the walls of the container

Gas pressure

• When a gas is held in a container, there is a constant force applied by the gas to the container

• The gas particles collide with the container walls

• In each collision, the gas particle exerts a tiny force upon impact which acts at right angles to the surface

• The net effect of many such collisions is a constant force on the surface area of the container

• Since pressure is force per unit area, the gas can be said to exert pressure on the container

• When the particles travel faster (e.g. at a higher temperature), they collide with walls more frequently

  • This means the gas exerts a greater pressure