Density is defined as mass per unit volume.
This means that lead is about 11 times more dense than water. There is a direct connection between density and sinking and floating. If an object is more dense than the liquid in which it is placed, the object will sink. If the object is less dense than the liquid it is placed in, it will float. The concept of density can be a little tricky because it applies to a substance itself as well as to an overall object made from the substance.