A skydiver jumps from an aircraft and falls vertically downwards. At first, the skydiver accelerates. After some time, the skydiver reaches terminal velocity. Explain why the skydiver's acceleration decreases to zero as they fall, before they open their parachute.

OCR GCSE Physics A: Gateway Science (J249) — P2.1 Motion · Explain · 4 marks · View as Markdown

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

A skydiver jumps from an aircraft at high altitude and falls through the atmosphere before opening their parachute.

Model answer (4 marks)

As the skydiver speeds up, the air resistance (drag) acting on them increases.
The weight of the skydiver remains constant, so the increase in drag reduces the net downward force.
According to Newton’s Second Law, a smaller net force gives a smaller acceleration.
When the drag force equals the weight, the net force is zero and the acceleration becomes zero – this is the terminal velocity.

Examiner tips

  • Use the term ‘air resistance’ or ‘drag’. Mention that weight is constant. Show the link to Newton’s Second Law (F=ma).
  • Explain that terminal velocity occurs when drag = weight, giving zero net force and zero acceleration.

Common mistakes

  • Saying the skydiver’s speed stops increasing without mentioning drag. Forgetting that weight is constant. Using the wrong sign for the forces or not linking to Newton’s Second Law.

Mark scheme (4 marks)

  1. As the skydiver speeds up, air resistance (drag) increases
  2. The resultant force decreases as air resistance increases (weight remains constant)
  3. A smaller resultant force means a smaller acceleration (reference to Newton's Second Law)
  4. At terminal velocity, air resistance equals weight, so the resultant force is zero and acceleration is zero

Key terms in this question

terminal velocity · acceleration

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