Density is used to make a fair comparison between materials.

Mass of empty measuring cylinder in g | Mass of measuring cylinder + water in g | Mass of water in g | Volume of water in cm^{3} |
---|---|---|---|

**Graph**

Plot a graph of mass in g on the y-axis against volume in cm^{}3 on the x-axis.

Draw a line of best fit through the points.

The gradient of the graph = = density of water.

Calculate the gradient of the graph and hence the density of water.

**Conclusion**

As for the previous experiment, the line of best fit is a straight line through the origin.

We can say that the volume of water is directly proportional to its mass.

As the volume of water increases its mass increases in direct proportion.

The gradient of the graph equals the density of water.

**Error**

The main cause of error in this experiment is reading the volume of water.

Care should be taken to read the volume at eye level, with the measuring cylinder placed on the bench.

The density of water changes with temperature so care must also be taken to keep the water at a constant temperature throughout the experiment.

**Sinking and floating**

An object or a liquid will float if it is less dense than the liquid beneath it.

Ice floats on top of water because the density of ice (0.9 g/cm^{3}) is less than the density of water (1.0 g/cm^{3})

A ship floats on water because the average density of the ship (metal from which it is made, cargo, people and air contained within it) is less than 1.0 g/cm^{3}.

Hot water floats on top of cold water because hot water is less dense than cold water.

Hot air rises because it is less dense than the surrounding cold air.