Pressure

Density is a property of a substance that is the mass per unit volume. Density is measured in units of kilograms per cubic meter. Specific Gravity is the density of the substance divided by the density of water. Pressure is the force per unit area. Pressure is measured in many different units, but in the SI system, it is measured in Newtons per square meter or Pascals. As you go deeper underwater, the pressure increases. The pressure underwater can be calculated if you know the pressure on the surface of the water, the depth of the water and the density of the water. 

Additional Resources

For more information on pressure view the video clip Density and Pressure from Discovery Education™ streaming.

You have probably had to put air in a tire to raise the pressure.  In NASCAR tires, accurate pressure is very important.  The heat generated in the tires during a race causes large increases in pressure.  By understanding pressure, the pit crew can prevent tire problems during a race.