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Practice questions · Friction and drag

Always opposing the motion.

Six original Cambridge-style questions on defining friction and drag, their direction, how drag grows with speed, useful and harmful friction, and where the energy goes.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
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Opposite to motion; grows with speed.

01
[2 marks]

What is friction? State the direction in which it acts on a moving object.

  • Friction is a force that opposes the relative motion of two surfaces in contact. ✓
  • It acts in the direction opposite to the motion. ✓
02
Analysis
[2 marks]

Give one situation where friction is useful and one where it is a nuisance.

  • Useful: gripping the road / walking / braking. ✓
  • Nuisance: wearing down moving parts / wasting energy as heat. ✓
03
Analysis
[2 marks]

State how the drag (air resistance) on a moving object changes as its speed increases, and give one consequence of this for a vehicle.

  • The drag increases as the speed increases. ✓
  • A larger driving force is needed to keep going at higher speeds (or fuel use is greater). ✓
04
Analysis
[2 marks]

A box is given a push along the floor and then slides to a stop. Explain, in terms of forces, why it slows down.

  • Once released, friction acts backward, opposite to the motion. ✓
  • This gives a resultant force backward, so the box decelerates until it stops. ✓
05
Analysis
[2 marks]

When friction acts between two surfaces that rub together, energy is transferred. State the main form the energy is transferred to, and one effect this can have.

  • Mainly to heat (thermal energy), with some sound. ✓
  • It warms the surfaces, which can cause wear or overheating of parts. ✓
06
Analysis
[3 marks]

A car travels at a steady high speed, then later at a steady low speed, both on a level road. Explain why a larger driving force is needed at the higher speed.

  • At any steady speed the resultant force is zero, so the driving force equals the total resistive force. ✓
  • Drag increases with speed, so the resistive force is larger at the higher speed. ✓
  • Therefore a larger driving force is needed to balance it. ✓