# Particle motion

The in a gas move very quickly in random directions. Collisions frequently happen between:

• particles
• particles and the wall of the container

The effect of collisions with the container is to produce a net acting on the container walls. This force acts at right angles to the container walls, which is detected as gas . This pressure can be measured using a pressure gauge.

For example, the collisions caused by a gas trapped inside a balloon cause forces to act outwards in all directions, giving the balloon its shape.

The pressure caused by a gas can be calculated using the equation:

$pressure = \frac{force}{area}$

This is when:

• pressure is measured in newtons per metre squared (N/m²)
• force is measured in newtons (N)
• is measured in metres squared (m²)

Another unit of pressure is the (Pa):

• 1 Pa = 1 N/m2
• 1 kPa = 1,000 Pa

A is a system where no substances can enter or leave, such as a balloon filled with air and tied off, or a . A gas in a closed system can be:

• by reducing its , which increases its pressure
• expanded by increasing its volume, which decreases its pressure.