Required Practical: Measuring Density

This lesson covers the AQA Required Practical for determining the density of regular and irregular solids and liquids (AQA 8464, Required Practical 15). You must understand the methods, equipment, calculations and sources of error involved.

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Measuring the Density of a Regular Solid

A regular solid has a simple geometric shape (cuboid, cylinder or sphere) whose volume can be calculated from measured dimensions.

Method

1. Measure the mass of the object using an electronic balance (in grams).
2. Measure the dimensions using a ruler, vernier calliper or micrometer:
   • Cuboid: measure length ($l$l), width ($w$w) and height ($h$h)
   • Cylinder: measure diameter (then calculate radius $r$r) and height ($h$h)
3. Calculate the volume:
   • Cuboid: $V = l \times w \times h$V=l×w×h
   • Cylinder: $V = \pi r^2 h$V=πr2h
4. Calculate density: $\rho = m / V$ρ=m/V.

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Measuring the Density of an Irregular Solid

An irregular solid (e.g. a stone or a key) does not have a simple shape, so you cannot calculate its volume from dimensions. Instead, use the displacement method.

Method 1: Measuring Cylinder