A skydiver jumps from an aeroplane and falls downward. At first the skydiver accelerates. After some time, the skydiver reaches terminal velocity. Explain why the skydiver first accelerates and then reaches terminal velocity.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A skydiver jumps from a stationary aeroplane at high altitude and falls vertically downward through the air.
Model answer (5 marks)
At the start the skydiver’s weight (mg) is larger than the upward air resistance, so the net force is downward and, by Newton’s second law, the skydiver accelerates downward.
As the speed increases, the drag force (which depends on velocity) grows.
When the drag equals the weight, the net force becomes zero.
With no net force the acceleration stops and the skydiver continues at a constant speed – the terminal velocity.
As the speed increases, the drag force (which depends on velocity) grows.
When the drag equals the weight, the net force becomes zero.
With no net force the acceleration stops and the skydiver continues at a constant speed – the terminal velocity.
Examiner tips
- Use the exact terms ‘weight’, ‘air resistance’, ‘net force’, ‘Newton’s second law’, ‘terminal velocity’.
- Show the sequence: weight > drag → acceleration; drag ↑ with speed → weight = drag → zero net force → constant speed.
Common mistakes
- Confusing drag with weight or ignoring that drag increases with speed.
- Failing to mention that the acceleration stops when forces balance, not that the skydiver ‘stops’ moving.
Mark scheme (5 marks)
- At the start, the weight (gravitational force) acting downward is greater than the air resistance (drag) acting upward
- There is a resultant (net) force downward, so the skydiver accelerates downward (Newton's Second Law)
- As the skydiver's speed increases, the air resistance (drag) increases
- Eventually air resistance becomes equal to the weight
- The resultant force is now zero, so the skydiver moves at a constant velocity (terminal velocity)
Key terms in this question
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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