Matter exists mainly in three states: solid, liquid, and gas.

Solids have a fixed shape and volume.

Liquids have a fixed volume but take the shape of their container.

Gases have neither fixed shape nor volume.

Plasma is a fourth state of matter found in stars and lightning.

Melting turns solids into liquids; freezing turns liquids into solids.

Evaporation turns liquids into gases.

Condensation turns gases into liquids.

Sublimation is when a solid turns directly into a gas.

Temperature and pressure affect the state of matter.