Density is the amount of mass an object has per each unit of volume. Density is key in the principle of buoyancy, which is credited to Archimedes. It is also used in determining which material to use for building planes, ships and other vehicles. If you have two objects of the same size, the one made of the denser material will weigh more. Heavier objects require more energy to move, so engineers try to find less dense materials to make vehicles more energy efficient.

Determine the radius of the sphere. You can do this by measuring the circumference, or distance around the sphere at the widest point and then dividing by 2?. For example, if the circumference is 62.8 inches, the radius would be 10 inches. ? can be approximated as 3.14.

Determine the volume of the sphere by multiplying 4/3 * R^3 where R is the radius. For example, if your radius was 3 inches, your formula would be 4/3 * 3^3 and your volume would be 36 cubic inches.

Determine the mass of the sphere by using a scale. Divide the mass of the sphere by the volume of the sphere. For example, if the mass were 10 lbs. and the volume was 2 cubic inches, the density would be 5 lbs. per cubic inch.

#### Warning

Make sure you report your units correctly otherwise your density will be significantly off.