Density (kgm-3) – mass per unit volume
The density of water is 1g/cm3
The density of air 0.001 g/cm3
Liquids may be expressed in g/cm3
Small solids may be expressed in g/cm3
Density is independent of quantity or shape
The density of a liquid if often less than a solid density of the same material
Density varies due to intermolecular spacing, and due to the mass of particles
Brownian Motion – the constant and random zig-zag motion of small solid particles in fluids 
Brownian Motion – the constant and random zig-zag motion of small solid particles in fluids
Fluid particles cannot be seen, and are therefore much smaller and have a lower mass than the visible suspended particles
Fluid particles move in random directions and with a range of speeds
Suspended particles move because they are struck by randomly moving fluid particles
Suspended particles move continuously because fluid particles are continuously moving
Evaporation – the process in which a liquid changes state to a gas. It can occur at all temperatures and has a cooling effect as particles take away kinetic energy from the system