Which equations do I need for density and pressure?

The core equations are density equals mass over volume (rho = m / V), pressure equals force over area (P = F / A), and the pressure due to a column of liquid (P = rho g h). Know the SI unit for each quantity: kilograms per cubic metre for density and pascals for pressure.

How do I measure the density of an irregular object?

Find the mass on a balance, then find the volume by displacement: lower the object fully into water in a measuring cylinder and the rise in the water level equals the object's volume. Then use density equals mass over volume.

Why does temperature stay constant during a change of state?

During melting or boiling the energy supplied goes into breaking the forces between particles rather than increasing their kinetic energy, so the temperature does not change. This shows as a flat section on a heating curve.

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Density, pressure and kinetic theory: study guide - CCEA GCSE Physics

A study guide to the density, pressure and kinetic theory topic of CCEA GCSE Physics: density and how to measure it, pressure in solids and liquids, the particle model and changes of state, gas pressure, and heat transfer and insulation.

Generated by Claude Opus 4.88 min readCCEA Unit 1Updated 2026-06-14

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this topic covers
How it is examined
The equations to recall
How to revise it

Density, pressure and kinetic theory brings together a calculation strand (density and pressure) and a particle-model strand (states of matter, gas pressure and heat transfer). Several parts are also practical-skills topics, so the experimental methods are examined.

What this topic covers

Density - density as mass per unit volume, $\rho = m / V$ , and methods to measure it for regular solids, irregular solids and liquids.
Pressure in solids and liquids - $P = F / A$ , and how liquid pressure increases with depth and density, $P = \rho g h$ .
Particle model and changes of state - the arrangement and motion of particles in solids, liquids and gases, the changes of state, and reading heating curves.
Gas pressure - how collisions of particles with the walls cause pressure, and how it changes with temperature and volume.
Heat transfer and insulation - conduction, convection and infrared radiation, surface colour, and methods of reducing unwanted heat loss.

How it is examined

Expect density and pressure calculations, descriptions of how to measure density, particle-model explanations of states of matter and gas pressure, heating-curve interpretation, and questions on insulating buildings. Many marks reward clear particle-level reasoning, so practise the standard explanations.

The equations to recall

Density: $\rho = \dfrac{m}{V}$ .
Pressure on a surface: $P = \dfrac{F}{A}$ .
Pressure in a liquid: $P = \rho g h$ .

How to revise it

Drill the calculations. Practise density and pressure problems, watching units carefully (especially cm to m conversions).
Learn the measurement methods. Be able to describe measuring density for regular and irregular solids and for liquids, with the sources of error.
Rehearse particle-model explanations. Write out how particles are arranged and how they move in each state, and why gas pressure changes with temperature and volume.
Practise heating curves. Explain the sloping and flat sections in terms of kinetic energy and breaking forces.
Know the three heat transfers. Link conduction, convection and radiation to particle behaviour and to ways of insulating a home.

Work through the linked dot points for full worked answers and exam-style questions on each part of the topic.

Sources & how we know this

CCEA GCSE Physics specification — CCEA (2017)