Pressure in gases

If you ride your bike over a bump in the road, you will be pleased that gases exert pressure on the walls of their container. A pumped-up tyre cushions the rider against bumps, but a flat tyre does not. The pressure of the air inside a flat tyre is just too low to do this.

Colliding particles

The particles in a gas move quickly in all directions, but they do not get far before they collide with each other or with the walls of their container. Gas pressure is caused when gas particles hit the walls of their container. The more often the particles hit the walls, and the faster they are moving when they do this, the higher the pressure.

This is why the pressure in a tyre or balloon goes up when more air is pumped in.

Shows gas particles moving around in a container. Some bounce off the sidesParticles of gas collide with each other and with their container walls

Heating increases pressure

If a gas is heated, its particles move around more quickly. They hit the walls of their container harder and more often. This increases the pressure. Sometimes the pressure gets so great that the container bursts.

This is why balloons and tyres burst if you blow them up too much. It is also why deodorant spray cans carry warning signs to tell you not to leave them in the sunshine. If they get too hot they may explode.