To calculate the density of an object we need to find out: How much matter it contains (mass). How much space it takes up (volume).
Mass is measured in grams, and the standard unit of volume is 1 centimetre cubed (cm3 density is usually expressed in grams per centimetre cubed, or g/cm3 g cm-3
.
Fig. 2 compares the mass of equal volumes (1 cm3 that:
l l
l l
The mass of 1 cm3 The mass of 1 cm3
of aluminium is 2.7 g of lead is 11.3 g
The density of a substance is its mass per unit volume. This means that: The density of aluminium is 2.7 g cm-3 The density of lead is 11.3 g cm-3
Comparing the mass of equal volumes in this way shows that lead is more dense than aluminium.
Aluminium Lead ) of two metals – aluminium and lead. It shows ), so , which is the same as
Fig. 2 Comparing the masses of 1 cm3
Using maths to calculate density We will not always have exactly 1 cm3
we can calculate the density using the formula: Density =
of aluminium and lead. of a substance to calculate its density in this way. However, Mass Volume
We can calculate the density of any substance by dividing the mass in grams by the volume in centimetres cubed. For example, 6 cm3
of aluminium has a mass of 16.2 g: Density = Mass Volume =
16.2 g 6 cm3
= 2.7 g cm-3
Did you notice that the result of this calculation, 2.7 g cm-3 we calculated above using the 1 cm3
, is the same value for density that block of aluminium? The density of a particular substance
is always the same even if we use different volumes of that substance to do our calculations. For example the density of a large sheet of aluminium foil is the same as the density of a small aluminium block. Density is a characteristic property of a substance.
