A motorcyclist is involved in a collision and slides along the road surface. Explain why wearing a helmet reduces the risk of serious head injury during this type of accident.

Eduqas GCSE Physics — 4.3 Safety in public transport · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Motorcycle helmets are compulsory in the UK. They are designed with a hard outer shell and a thick layer of cushioning foam inside.

Model answer (4 marks)

A helmet increases the time over which the head decelerates, because the hard shell and foam keep the head moving for a longer period before it stops.

A longer deceleration time reduces the average force on the head (F=Δp/Δt), so the head experiences a smaller impact force.

The foam inside the helmet compresses and deforms during the collision, absorbing kinetic energy and further reducing the force transmitted to the skull.

With a lower force on the head, the skull and brain are less likely to suffer fractures or severe injury, reducing the risk of serious head injury.

Examiner tips

  • Use the formula F=Δp/Δt to justify the force reduction
  • Mention both the shell and foam in the same sentence
  • Show the causal chain: longer time → lower force → less damage

Common mistakes

  • Failing to mention the foam’s role in energy absorption
  • Confusing ‘time’ with ‘distance’ in the deceleration discussion
  • Using vague terms like ‘less impact’ without linking to force

Mark scheme (4 marks)

  1. The helmet increases the time over which the head decelerates (comes to rest)
  2. A longer deceleration time means the force acting on the head is reduced
  3. The foam compresses / deforms to absorb energy during the collision
  4. Less force on the head means less damage to the skull / brain, reducing the risk of serious injury

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