Pearson Edexcel International GCSE in Physics · 4PH1 · Free · no account needed
Topic 5 · Solids, liquids and gases
Density and pressure, pressure in fluids, changes of state, specific heat capacity, and the particle model that explains gas pressure and the two gas laws.
Every lesson here ends the same way: learn it, teach it to an AI pupil who asks the awkward question, then defend it against the thinker with the strongest claim on it — free · no account needed.
7 lessons, covering 22 specification statements.
What you need to know — the 22 statements, and where each one is taught
Every statement this topic carries, in the specification's own numbering, with Incandio's restatement of what it asks and the lesson that discharges it. Tick them off against your own copy of the specification: this is the topic's revision checklist, not a summary of it. Incandio is aligned to this specification. It is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording — the statement numbers are given so you can check every lesson against your own copy.
| Statement | What it asks | Taught in |
|---|---|---|
| 5.1 | Use the units °C, K, J, kg, kg/m³, m, m², m³, m/s, m/s², N and Pa | Density |
| 5.3 | Use density = mass ÷ volume | Density |
| 5.4 (practical) | Practical: investigate density using direct measurements of mass and volume | Density |
| 5.5 | Use pressure = force ÷ area | Pressure, and Pressure in Liquids |
| 5.6 | Pressure at a point in a gas or liquid at rest acts equally in all directions | Pressure, and Pressure in Liquids |
| 5.7 | Use pressure difference = height × density × gravitational field strength | Pressure, and Pressure in Liquids |
| 5.8 | Why heating a system changes its stored energy and raises temperature or changes state | Particles and Changes of State |
| 5.9 | The changes that occur when a solid melts and when a liquid evaporates or boils | Particles and Changes of State |
| 5.10 | The arrangement and motion of particles in solids, liquids and gases | Particles and Changes of State |
| 5.11 (practical) | Practical: obtain a temperature–time graph showing constant temperature during a change of state | Particles and Changes of State |
| 5.2 | Use the unit J/kg °C | Specific Heat Capacity |
| 5.12 | Specific heat capacity defined, in J/kg °C | Specific Heat Capacity |
| 5.13 | Use Q = m × c × ΔT | Specific Heat Capacity |
| 5.14 (practical) | Practical: investigate the specific heat capacity of water and some solids | Specific Heat Capacity |
| 5.15 | How random molecular motion in a gas exerts a force, and hence a pressure, on the container walls | Gas Pressure and Absolute Zero |
| 5.16 | Why there is an absolute zero of temperature at −273 °C | Gas Pressure and Absolute Zero |
| 5.17 | The Kelvin scale, and converting between Kelvin and Celsius | Gas Pressure and Absolute Zero |
| 5.18 | Why a rise in temperature increases the average speed of gas molecules | The Kinetic Theory of Gases |
| 5.19 | Kelvin temperature is proportional to the average kinetic energy of the molecules | The Kinetic Theory of Gases |
| 5.20 | The qualitative relationships between pressure and volume, and pressure and Kelvin temperature | The Kinetic Theory of Gases |
| 5.21 | Use p₁ ÷ T₁ = p₂ ÷ T₂ | The Gas Laws |
| 5.22 | Use p₁V₁ = p₂V₂ | The Gas Laws |
The lessons
- Density — Not how heavy something is, but how much of it is packed into the space it occupies. (5.1, 5.3, 5.4)
- Pressure, and Pressure in Liquids — Why a drawing pin works, why pressure at a point pushes every way at once, and why depth is the only thing that matters underwater. (5.5, 5.6, 5.7)
- Particles and Changes of State — What the particles are doing in each state — and why a boiling pan stays at 100 °C however hard you heat it. (5.8, 5.9, 5.10, 5.11)
- Specific Heat Capacity — Why the sand burns your feet and the sea is freezing on the same afternoon. (5.2, 5.12, 5.13, 5.14)
- Gas Pressure and Absolute Zero — Where the pressure of a gas actually comes from, and why the temperature scale has to start somewhere else. (5.15, 5.16, 5.17)
- The Kinetic Theory of Gases — One picture — fast random molecules bouncing off walls — that predicts everything a gas does. (5.18, 5.19, 5.20)
- The Gas Laws — Two equations that put numbers on everything the previous page explained. (5.21, 5.22)