# 6. Gas in a container

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## Holding a gas in a container

A gas exerts a pressure on the walls of a container. Why is that?

A gas is made up of lots of high speed particles (atoms, molecules) zooming around in straight lines until they collide with the walls of the container.

In each collision, a force is exerted on the wall by the particle as it bounces off.

In the same way, the air around us collides with our skin trillions times each second. All of those collisions create a force which acts upon an area, making a pressure.

Pressure = Force / Area

So the collisions exert force over the area of the wall, creating a pressure.

If you added some more thermal energy to the gas, you increase the kinetic energy of the particles, making them move faster. This means that they will collide with more force andÂ more frequently.

So increasing the temperature (a measure of the kinetic energy of the gas particles) will increase the force of each collision and that will create a larger pressure acting on the walls of the container. A good example of this is in a pressure cooker.