Pearson Science Double Award Physics 5: Solids, Liquids and Gases

This topic connects bulk density and pressure to forces and the random motion of gas molecules. The 4SD0 Double Award boundary includes density, pressure difference and fixed-mass gas relationships. Particle-state detail, specific heat capacity, latent heat and related points 5.2 and 5.8 to 5.14 belong to separate Physics.

Density

Density is mass per unit volume:

$$\rho=\frac{m}{V}.$$

Use compatible units, commonly kilograms per cubic metre or grams per cubic centimetre. A material's density does not depend on sample size when conditions are unchanged, but an object's average density can reflect hollow spaces or mixed materials.

For a regular solid, measure dimensions and calculate volume. For an irregular solid that sinks and does not react or dissolve, use water displacement. Read the lower meniscus at eye level, remove trapped bubbles and ensure complete submersion. Measure mass with a zeroed balance. Repeats reduce random reading variation.

Pressure in solids and fluids

Pressure is normal force per unit area:

$$p=\frac{F}{A}.$$