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Matter is made up of atoms about 0.1 nm in size. Atoms and molecules are arranged differently in solids, liquid and gases. Density is calculated from mass divided by volume.

Changes in temperature or physical state are caused by transfers of energy. Specific heat capacity determines the energy needed to change temperature, and specific latent heat to change state.

Gases and liquids exert pressures on objects and the walls of their containers due to collisions. The greater the force and frequency of these collisions, the greater the pressure.