• 2 minutes

• Diffusion is the movement of a substance from an area of high concentration to an area of low concentration. 

• Diffusion happens in liquids and gases because their particles move randomly from place to place. 

• Diffusion is an important process for living things; it is how substances move in and out of cells.

• To learn more from BBC Bitesize - What is Diffusion?

Thermal expansion occurs when an object expands or gets larger due to an increase in its temperature. Thermal expansion occurs because heated molecules move faster and take up more space.

There are three types of thermal expansion depending on the dimension that undergo change and that are linear expansion, areal expansion and volumetric volume.