Syllabus Edition

First teaching 2020

Last exams 2024

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Terminal Velocity (CIE AS Physics)

Revision Note

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Katie M

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Katie M

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Terminal Velocity

  • For a body in free fall, the only force acting is its weight and its acceleration g is only due to gravity.
  • The drag force increases as the body accelerates
    • This increase in velocity means the drag force also increases

  • Due to Newton’s Second Law, this means the resultant force and therefore acceleration decreases (recall F = ma)
  • When the drag force is equal to the gravitational pull on the body, the body will no longer accelerate and will fall at a constant velocity
    • This the maximum velocity that the object can have and is called the terminal velocity

 

Terminal Velocity diagram (1), downloadable AS & A Level Physics revision notes

Terminal Velocity diagram (2), downloadable AS & A Level Physics revision notes

Terminal Velocity diagram (3), downloadable AS & A Level Physics revision notes

A skydiver in freefall reaching terminal velocity

 
  • The graph shows how the velocity of the skydiver varies with time
  • Since the acceleration is equal to the gradient of a velocity-time graph, the acceleration decreases and eventually becomes zero when terminal velocity is reached

Worked example

Skydivers jump out of a plane at intervals of a few seconds.

Skydivers A and B want to join up as they fall.

WE - Terminal velocity question image, downloadable AS & A Level Physics revision notes

If A is heavier than B, who should jump first?

  • Skydiver B should jump first since he will have a lower terminal velocity
  • This is because skydiver A has a greater mass, and hence, weight
  • Terminal velocity is reached when weight is equal to air resistance
  • Therefore, a higher terminal velocity means that skydiver A will have a greater speed, and will reach terminal velocity faster than skydiver B

Examiner Tip

  • Exam questions about terminal velocity tend to involve the motion of skydivers as they fall
  • A common misconception is that skydivers move upwards when their parachutes are deployed - however, this is not the case, they are in fact decelerating to a lower terminal velocity
  • What do you think this would look like on the graph above?

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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.