Matter is made up of small particles called atoms. Atoms can exist on their own or together as molecules. Atoms are very small and around 100,000,000 of them side by side would measure 1 centimetre.

There are different ways to investigate density. In this required practical activity, it is important to:

- record the mass accurately
- measure and observe the mass and the volume of the different objects
- use appropriate apparatus and methods to measure volume and mass and use that to investigate density

To measure the density of various materials.

**Method 1: Regular solids - cube or sphere **

- Use a ruler to measure the length (
*l*), width (*w*) and height (*h*) of a steel cube. - Place the metal cube on the top pan balance and measure its mass.
- Calculate the volume of the cube using (
*l*×*w*×*h*). - Use the measurements to calculate the density of the metal.
- Use vernier callipers to measure the diameter of the sphere.
- Place the metal sphere on the top pan balance and measure its mass.
- Calculate the volume of the sphere using
- Use the measurements to calculate the density of the metal.

**Method 2: Stone or other irregular shaped object **

- Place the stone on the top pan balance and measure its mass.
- Fill the displacement can until the water is level with the bottom of the pipe.
- Place a measuring cylinder under the pipe ready to collect the displaced water.
- Carefully drop the stone into the can and wait until no more water runs into the cylinder.
- Measure the volume of the displaced water.
- Use the measurements to calculate the density of the stone.

**Method 3: Water (or any liquid)**

- Place the measuring cylinder on the top pan balance and measure its mass.
- Pour 50 cm
^{3}of water into the measuring cylinder and measure its new mass. - Subtract the mass in step 1 from the mass in step 2. This is the mass of 50 cm
^{3}of water. - Use the measurements to calculate the density of the water.

Some example results could be:

Object | Mass (g) | Volume (cm³) | Density (g/cm³) | Density (kg/m³) |
---|---|---|---|---|

Steel cube | 468 | 60 | ||

Steel sphere | 33 | 4.19 | ||

Stone | 356 | 68 | ||

Water | 50 | 50 |

Using those results, the densities can be calculated using:

Density = mass ÷ volume

Mass of steel cube = 468 g

Volume of steel cube = 60 cm^{3}

Density = mass ÷ volume = 468 ÷ 60 = 7.8 g/cm^{3} (= 7,800 kg/m^{3} )

Diameter of steels sphere = 2 cm

Mass of steel sphere = 33 g

Volume of steel sphere = = 4.19 cm^{3}

Density = mass ÷ volume = 33 ÷ 4.19 = 7.9 g/cm^{3} (= 7,900 kg/m^{3} )

For a stone of mass 356 g, the volume of water displaced into the measuring cylinder is 68 cm^{3}

Density = mass ÷ volume = 356 ÷ 68 = 5.2 g/cm^{3} (= 5,200 kg/m^{3} )

Mass of 50 cm^{3} of water is found to be 50 g. Density = mass ÷ volume = 50 ÷ 50 = 1 g/cm^{3} (= 1,000 kg/m^{3} )

- Density can be measured for regular solids, irregular solids and liquids
- Densities calculated from measurements are subject to experimental error this could be because:
- the top pan balances used by different people may not be identically calibrated
- the resolution of the measuring cylinders may be different, causing different values for the volume to be recorded
- the displacement can may not have been set up correctly each time so that another added drop of water would cause some to dribble out of the spout before use

- The experiment above shows steel to have two different values for density: 7.8 g/cm
^{3}and 7.9 g/cm^{3}. One reason for this may be that some measurements were taken to different numbers of significant figures, and this can create rounding errors affecting the last significant figure of the answer. It could also mean that the actual value may be between 7.8 g/cm^{3}and 7.9 g/cm^{3}

Hazard | Consequence | Control measures |
---|---|---|

Water spilled from displacement can | slip and fall | use a measuring cylinder to collect displaced water and prevent spills |