Explain why a skydiver reaches a terminal velocity before opening their parachute.

AQA GCSE Physics (8463) — 4.5.6 Forces and 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 and falls towards the ground. After a period of acceleration, the skydiver reaches a constant speed called terminal velocity.

Model answer (4 marks)

Initially the skydiver’s weight is greater than the air resistance, so the resultant force is downwards and the skydiver accelerates.
As the speed increases, the air resistance increases.
The increasing air resistance reduces the magnitude of the resultant force.
When the air resistance equals the weight, the resultant force becomes zero and the skydiver moves at a constant speed – the terminal velocity.

Examiner tips

Show the sequence of forces changing with speed
Use the term ‘resultant force’ and ‘air resistance’
Explain that zero resultant force gives constant speed

Common mistakes

Confusing air resistance with weight as the cause of acceleration
Forgetting to mention that air resistance starts at zero
Using vague terms like ‘slow down’ instead of ‘decrease resultant force’

Mark scheme (4 marks)

Initially the resultant force is downwards (weight greater than air resistance / air resistance is zero at the start)
As the skydiver accelerates, air resistance increases
The resultant force decreases as air resistance increases
At terminal velocity the resultant force is zero because weight equals air resistance, so the skydiver moves at constant speed

Key terms in this question

terminal velocity