AIR RESISTANCE AND TERMINAL VELOCITY
4 marks · NormalExplain how terminal velocity is reached by a falling object. In your answer, refer to what happens to the forces acting on the object during its fall.
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When an object begins to fall, only its weight acts downwards and it accelerates. As speed increases, air resistance grows up until it matches the weight. At this point, the forces are balanced and the object moves at a constant speed (terminal velocity).
Must show: Weight acts downwards; initial acceleration, Air resistance increases with speed, Terminal velocity when forces balance, Constant speed after terminal velocity
Common mistakes: Forgetting that air resistance increases with speed; Not mentioning forces are balanced at terminal velocity
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Marking points
B1 · 1 mark · States that initially weight acts down, resulting in acceleration.
B2 · 1 mark · Describes air resistance increasing as speed increases.
B3 · 1 mark · Explains that terminal velocity is reached when air resistance equals weight (balanced forces).
B4 · 1 mark · States that at terminal velocity, the object falls at a constant speed.
Worked solution
When an object is released, the only force acting is its weight and it accelerates downwards. As it speeds up, air resistance increases upwards. When air resistance becomes equal to weight, there is no net force, so the object moves at constant speed — this speed is called terminal velocity.