Define density.

Density is a word that is used to describe how much space an object or substance takes up (its volume) in relation to the amount of matter in that object or substance (it's mass).

We can also define it as, the amount of mass per unit of volume. If an object is heavy and compact, it has a high density. If an object is light and takes up a lot of space, it has a low density.

So, if we know the volume and mass of an object, we can calculate the density by using the equation.

$\displaystyle Density=\ \frac{Mass}{Volume}$

• The density of an object is affected by the positioning of molecules.

• Objects with tightly packed molecules are denser than those where the molecules are spread out.

• Objects that are denser than water sink and those less dense float. 

• Hollow things often float too as air is less dense than water.