Density
A substance's mass per unit volume.
Unit Density
Formula
Mass
Measure of the amount of matter a substance contains.
Unit Mass
Formula
Volume
The amount of space taken up by a substance.
Unit Volume
Formula
Weights on a Balance
Two weights balanced on a beam on a pivot at its center, positioned at equal distances from the pivot, have equal mass.
If they differ in weight, the heaver weight has to be closer to the pivot. Also the weights multiplied by their distances from the fulcrum are equal.