A football is left outside on a cold winter night. When the ball is brought back indoors into a warm room, it feels harder. Explain why the pressure inside the football increases when its temperature rises. Assume the volume of the football does not change.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The gas molecules inside the football have greater kinetic energy at a higher temperature, so they move faster. Faster molecules collide with the walls more often and with greater force. Pressure is the perpendicular force per unit area on the walls; therefore, the increased collision force raises the pressure inside the ball.
Examiner tips
- Use the term ‘kinetic energy’ and ‘collide with the walls’ to show understanding of the gas law. Mention that volume is constant to justify the pressure change. Keep the explanation concise and directly linked to the marks.
Common mistakes
- Confusing temperature with pressure, or saying the volume changes.
Mark scheme (4 marks)
- The gas particles (molecules) inside the football move faster / have greater kinetic energy at a higher temperature
- The particles collide with the walls of the football more frequently
- The particles also collide with the walls with greater force
- Pressure is the perpendicular force per unit area on the walls, so greater force from collisions means greater pressure
Key terms in this question
Related
- All WJEC GCSE Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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