Gas - GCSE Physics Definition

In GCSE Physics, "gas" refers to one of the states of matter. Unlike solids, which have fixed shapes, or liquids, which maintain a constant volume but take the shape of their container, gases have no fixed shape or volume. The particles in a gas are spread far apart and move freely at high speeds, which allows them to expand and fill the available space. This behaviour is explained by the kinetic theory of gases, which states that the particles are in constant, random motion and exert pressure on the walls of a container when they collide with it. Gas behaviour is also influenced by factors such as temperature and pressure, which are key concepts in understanding gas laws.