Introduction to density
Physical properties
The physical properties of a substance are characteristic of that substance and can be used to identify the substance. Characteristics are properties that do not depend on the amount of substance used to make the measurement. Melting temperature and boiling temperature are physical properties.
Density
Density is a measure of the mass per unit volume. Per means divide by.
Thus, as shown in the mathematical relationship, density is calculated by dividing the mass of the object by its volume.
When considering the densities of pure substances, in general the density of solids is greater than liquids. Liquids are in turn more dense than gases.
Floating and sinking
Objects float above the surface of a liquid if the density of the object overall is less than the density of the liquid.
The extent to which an object sinks in a liquid is dependent on Archimedes principle that says that volume of liquid displaced by the object has a mass equal to the mass of the object.
The physical properties of a substance are characteristic of that substance and can be used to identify the substance. Characteristics are properties that do not depend on the amount of substance used to make the measurement. Melting temperature and boiling temperature are physical properties.
| d = | m |
| V |
Density is a measure of the mass per unit volume. Per means divide by.
Thus, as shown in the mathematical relationship, density is calculated by dividing the mass of the object by its volume.
substance | phase | density /g cm–3 |
| air | gas | 0.0011 |
| water | liquid | 1.0 |
| copper | solid | 8.9 |
 |  |  |
| Gas density lower - | liquid densities higher - | solid densities highest |
Floating and sinking
Objects float above the surface of a liquid if the density of the object overall is less than the density of the liquid.
A ship floats because although it is made of steel which is more dense than water, it encloses a volume of air and the resulting shape has an average density less than that of the water.
The extent to which an object sinks in a liquid is dependent on Archimedes principle that says that volume of liquid displaced by the object has a mass equal to the mass of the object.
This means that the same object will float "higher" in a more dense liquid and "lower" in a less dense liquid because for the more dense liquid a smaller volume of liquid has the same mass as the object.