Air Pressure and Density
Pressure is a force exerted on or against an object by being in contact with a substance. Thus, air pressure is due to the bombardment of the air (gas) particles with a surface. Density is defined as the mass per volume of a substance. Thus, air density is defined as the mass of air per unit volume.
Air Pressure and Temperature
The relationship between the two is that air temperature changes the air pressure. For example, as the air warms up the molecules in the air become more active and they use up more individual space even though there is the same number of molecules. This causes an increase in the air pressure.