IGCSE 0625 / Section 2.1 / Core

Pressure is a storm of collisions.

A balloon stays inflated because, every instant, millions of air molecules slam into its inner surface. Each tiny impact is nothing on its own, but together they push the walls outward. Heat the gas and the bombardment grows fiercer.

The key idea

Gas pressure is caused by particles colliding with the walls of their container. Each collision pushes on the wall, and the force of these collisions per unit area is the pressure. Raising the temperature makes the particles move faster, so they hit the walls harder and more often, raising the pressure.

Definition · learn the exact words

The pressure of a gas is caused by its particles colliding with the walls of the container; it is the force of these collisions acting per unit area of wall.

at constant volume: pressure rises as temperature (in K) rises

Pressure comes from collisions, not from particles statically pressing on the walls.

Section 01

Heat it, and feel the push.

Change the temperature of a trapped gas and watch how the collisions, and so the pressure, change.

Stage 1 · Learn

Check gas pressure

Four quick checks. Each correct answer earns XP and lights this skill on your star map.

Quick check+10 XP

Gas pressure is caused by...

Quick check+10 XP

If a fixed mass of gas is heated at constant volume, the pressure...

Quick check+10 XP

Each collision of a particle with the wall delivers a small...

Quick check+10 XP

At a higher temperature the gas particles move...

Section 02

Faster particles, harder hits.

Every part of the behaviour follows from how often and how hard the particles strike the walls.

Examiner trap

Gas pressure is the result of particles striking the walls, not of the particles simply pressing against them while still. When you heat a gas at constant volume, the pressure rises because the same particles collide with the walls more frequently and with greater force.

Stage 2 · Exam

Exam-style questions

Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.

Finish the four checks above to unlock the exam questions
Exam style+20 XP

A sealed rigid can of gas is heated. The pressure inside rises because the particles...

Exam style+20 XP

Doubling the kelvin temperature of a fixed mass of gas at constant volume roughly...

Exam style+20 XP

Gas pressure is best described as the...

Skill unlocked

Gas pressure, mastered.

Three particle-model skills down. Keep the chain going.

-Rank -Level -Score -Topics
Go deeper · practice
Six original Cambridge-style questions
How collisions create gas pressure, the effect of temperature at constant volume, and why kelvin is used. Attempt each, then reveal the worked solution.
Stage 3 · master the unit
Thermal physics challenge
Mixed questions across the whole unit, each one worth XP. Start this only when you feel confident across every topic in the unit, not just gas pressure.
Start the unit challenge →