A skydiver jumps from an aircraft and falls towards the ground. Initially, the skydiver accelerates rapidly. After some time, the skydiver reaches a constant velocity known as terminal velocity. Explain why the skydiver first accelerates and then reaches terminal velocity.

OCR GCSE Physics A: Gateway Science (J249) — P2.3 Forces in action · Explain · 4 marks · View as Markdown

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

A skydiver of mass 80 kg jumps from an aircraft at high altitude and falls freely before opening a parachute.

Model answer (4 marks)

Initially the skydiver’s weight (mg) exceeds the air resistance, giving a net downward force and acceleration (Newton’s 2nd law). As the speed increases the drag force rises, reducing the net force. When the drag equals the weight the forces balance, the resultant force is zero and acceleration stops. The skydiver then falls at a constant terminal velocity.

Examiner tips

  • Use the terms weight, air resistance, net force, acceleration, terminal velocity and state the balance of forces. Include Newton’s 2nd law to justify acceleration. Mention that drag increases with speed.

Common mistakes

  • Confusing drag with weight or ignoring that drag increases with speed; not stating that terminal velocity occurs when forces are balanced.

Mark scheme (4 marks)

  1. Initially, the weight (gravitational force) is greater than the air resistance / drag force
  2. There is a resultant / unbalanced force downwards, so the skydiver accelerates (Newton's First/Second Law)
  3. As speed increases, air resistance / drag increases
  4. Terminal velocity is reached when air resistance equals weight / forces are balanced / resultant force is zero, so there is no more acceleration

Key terms in this question

terminal velocity

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