Depending on the temperature, a substance can be in the form of a solid, a liquid or a gas.
For example, at room temperature, water is a liquid. However, when heated, it turns into water vapour, which is a gas. When water is put in a freezer, the temperature decreases, so it turns into ice, which is a solid.
Physical changes do not change the nature of the substance or the particles (they are the same in all three states), but their arrangement and movement are different.
Matter can change between states and there are 5 different changes of state, which you can see below.
Melting: This is the process that changes a solid to a liquid. When a solid is heated, the particles begin to vibrate as they gain more energy. This causes the forces between the particles to become weak.
Boiling: Otherwise known as vaporisation, this process changes a liquid to a gas. As mentioned, adding heat to a liquid will cause the particles to vibrate and move around even more. This also causes the bonds between the particles to break, forming a gas.
Condensation: This process changes a gas to a liquid. To go from a gas to a liquid, the gas needs to be cooled. This causes bonds to form between the particles, which causes liquid formation.
Freezing: This process changes a liquid to a solid. To freeze a liquid, it will need to be cooled, which causes bond formation.
Sublimation: Under certain conditions, a solid can turn into a gas. An example of this is the sublimation of iodine.
Materials store internal energy. When a substance is heated, its internal energy increases. and when a substance is cooled down, its internal energy decreases.
When a substance changes state, the mass does not change. Only the arrangement, closeness and motion of the particles change. This is known as the conservation of mass.