What causes thermal expansion in solids, liquids, and gases?

Thermal expansion in solids, liquids, and gases is caused by the increase in kinetic energy of their particles.

When a substance is heated, its particles gain kinetic energy and start to move more rapidly. This increased movement causes the particles to collide more frequently and with greater force, which in turn pushes them further apart. This process of particles moving further apart due to increased kinetic energy is what causes thermal expansion.

In solids, the particles are closely packed together in a fixed, regular pattern. When heated, these particles vibrate more vigorously about their fixed positions, causing the solid to expand. However, the expansion in solids is relatively small because the particles are already so close together and their movement is restricted.

In liquids, the particles are less closely packed and can move around more freely than in solids. When a liquid is heated, its particles move faster and spread out, causing the liquid to expand. The expansion in liquids is generally greater than in solids because the particles have more freedom to move.

In gases, the particles are far apart and move randomly at high speeds. When a gas is heated, its particles gain even more kinetic energy and move even faster, causing the gas to expand. The expansion in gases is much greater than in solids or liquids because the particles are already far apart and have a lot of freedom to move.

In summary, thermal expansion in solids, liquids, and gases is caused by the increase in kinetic energy of their particles when they are heated. This increased kinetic energy causes the particles to move more rapidly and spread out, resulting in expansion. The degree of expansion depends on the state of the substance, with gases expanding the most and solids the least.