This mini-lesson walks you through the whole of OCR Gateway P1 — Matter: the particle model, density, changes of state, specific heat capacity and latent heat, gas pressure, and the structure of the atom and how that model was built.
Work through each screen, answer the questions as you go (some wordy, some calculations) and collect ⭐ stars. Higher-tier-only points are flagged. Press Start when you're ready.
Everything is made of tiny particles. The kinetic particle model explains the three states by how those particles are arranged, how strongly they are held, and how they move:
Watch out: there is nothing between the particles — the gaps are empty space, not air or vapour. Heating gives particles more energy in their kinetic store, so they move faster and (in solids/liquids) vibrate more and spread a little further apart.
Tap the state of matter that each description fits best.
Density tells you how much mass is squeezed into a given volume. It is the property that lets the particle model explain why a brick sinks and a sponge floats:
The Greek letter ρ ("rho") stands for density. The same equation works in g/cm³ — just keep your units consistent. Water is 1000 kg/m³ (1 g/cm³).
Why states differ: a solid and its liquid have particles close together, so their densities are similar and fairly high. A gas has its particles spread far apart, so its density is much lower — same particles, far bigger volume.
A metal block has mass 600 kg and volume 0.25 m³.
ρ = 600 ÷ 0.25 = 2400 kg/m³
To find a density you need a mass and a volume:
Mass is conserved: if you reshape a lump of plasticine, or pour a liquid between beakers, the mass does not change — so if the volume changes, the density changes with it. Density depends on how the same mass is spread through a volume.
Heating or cooling can move a substance between states. These are physical changes — no new substance is made, and the change can be reversed to recover the original material:
Mass is conserved in every change of state. When ice melts or water boils, the particles are unchanged — none are created or destroyed — so the mass of the substance stays exactly the same. The particles just gain or lose energy and rearrange.
The internal energy of a material is the total energy of all its particles: the energy in their kinetic stores (motion → temperature) plus the energy in the bonds between them.
Heat a substance steadily and its temperature rises — except during a change of state. On the flat parts of the heating curve the energy is breaking bonds, not speeding particles up, so the temperature stays constant. That energy is the latent heat.
Misconception alert: on a plateau the substance is still gaining energy — that energy (the latent heat) is breaking the forces between particles. "No temperature change" does not mean "no energy is being absorbed".
To change a material's temperature (while it stays in one state) you change the energy in its thermal store. How much energy that takes depends on the specific heat capacity, c:
The specific heat capacity is the energy needed to raise 1 kg of a substance by 1 °C. Water's is high (4200 J/kg°C), which is why it heats and cools slowly.
Required practical: heat a known mass of metal block with an electric heater, recording the energy supplied (joulemeter) and the temperature rise, then find c = ΔE ÷ (m Δθ). Don't confuse specific heat capacity (warming up, temperature changes) with latent heat (changing state, temperature constant).
Heating 0.5 kg of water (c = 4200) by 20 °C:
ΔE = 0.5 × 4200 × 20 = 42 000 J (42 kJ)
To change a substance's state (at constant temperature) you supply the latent heat. How much depends on the mass and the specific latent heat, L:
The specific latent heat is the energy needed to change the state of 1 kg of a substance with no change in temperature. There are two kinds:
Melting 0.2 kg of ice (L = 334 000 J/kg):
E = 0.2 × 334 000 = 66 800 J (66.8 kJ)
Gas particles move quickly in random directions. Each time a particle collides with a wall of its container it bounces off, exerting a tiny force on the wall. Billions of these collisions every second add up to gas pressure.
Heat the gas and the particles move faster: they hit the walls harder and more often, so (at constant volume) the pressure rises as temperature rises.
Misconception alert: gas pressure is not the particles pushing on each other or "wanting to escape". It is simply the result of countless particle–wall collisions.
For a fixed mass of gas at constant temperature, squeeze it into a smaller volume and the particles hit the walls more often (less room to travel between hits), so the pressure rises. Pressure and volume are inversely related:
So halving the volume doubles the pressure. This is a Higher-tier-only calculation in OCR Gateway P1.
A gas at 100 kPa fills 0.30 m³. It is squeezed to 0.10 m³ at constant temperature.
p₂ = p₁V₁ ÷ V₂ = (100 × 0.30) ÷ 0.10 = 300 kPa
An atom is a tiny, dense, positively charged nucleus of protons and neutrons, surrounded by electrons in energy levels (shells). Almost all the mass is in the nucleus; the nuclear radius is far smaller than the radius of the whole atom.
Misconception alert: isotopes differ in neutrons, not protons — change the number of protons and you change the element entirely. And remember the atom is mostly empty space between the nucleus and the electrons.
Tap a label, then tap the box where that particle is found.
The model of the atom changed as new evidence arrived — a great example of how science self-corrects:
Energy levels: an electron can move up a level by absorbing electromagnetic radiation, and falls back down by emitting EM radiation. The energy of the radiation matches the gap between the levels.
The atmosphere is a "sea" of air around the Earth. Like any fluid, its particles collide with surfaces, so the weight of the air above you presses down — that is atmospheric pressure. A simple model treats the air as having roughly uniform density (we ignore the layers).
As you climb higher, there is less air above you, so fewer particles press down and the atmospheric pressure falls. That is why pressure drops up a mountain and why aircraft cabins are pressurised.
Watch out: "suction" is really a pressure difference. When you drink through a straw you lower the pressure inside it, and the higher atmospheric pressure outside pushes the liquid up — the straw does not "pull" it.
A liquid is also a fluid, so it presses on every surface it touches at right angles. The deeper you go, the more liquid sits above that point, so the greater its weight and the higher the pressure. The pressure due to a column of liquid is:
Misconception alert: liquid pressure depends only on the depth and the density of the liquid (and g) — not on the shape or width of the container. A wide tank and a thin tube of water filled to the same depth have the same pressure at the bottom.
Pressure 3 m below the surface of water (ρ = 1000 kg/m³, g = 10 N/kg):
p = h ρ g = 3 × 1000 × 10 = 30 000 Pa
Because pressure increases with depth, the liquid pushes up harder on the bottom of a submerged object than it pushes down on the top. That difference in pressure gives a resultant upward force called upthrust (buoyancy).
Misconception alert: floating is not simply about "light" or "small" objects. A huge ship floats and a tiny steel ball-bearing sinks. What matters is whether the upthrust can match the weight — i.e. the object's average density versus the liquid's.
Density: ρ = m ÷ V
Heating (temperature change): ΔE = m c Δθ
Changing state (constant temperature): E = m L
Gas (Higher only): p V = constant
Atmospheric pressure: falls with height (less air above)
Liquid pressure (Higher only): p = h ρ g → upthrust → floating depends on average density
Atom: Z = protons, A = protons + neutrons, neutrons = A − Z
Isotopes: same protons, different neutrons
You've covered all of OCR Gateway P1 — the particle model, density, changes of state with conservation of mass, internal energy, specific heat capacity and latent heat, gas pressure (and the Higher-tier pV = constant), atomic structure and the development of the atomic model. Press Finish to see your score.
You've worked through Matter for OCR Gateway GCSE Physics A. 🎉
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Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.