Terminal Velocity (Edexcel IGCSE Physics)

Terminal velocity

• Terminal velocity is the fastest speed that an object can reach when falling

• Terminal velocity is reached when the upward and downward acting forces are balanced

  • The resultant force on the object reaches zero

  • The object no longer accelerates and a constant terminal velocity is reached

Falling objects

• Falling objects experience two forces:

  • Weight 

  • Air resistance 

• The force of air resistance increases as the object's speed increases

• This is because the object collides with air particles as it moves through the air

  • The faster the object is travelling, the more collisions it has with the air particles

• The weight of the object does not change

• This is because 

  • The mass, , of the object does not change

  • The acceleration of freefall, , does not change

Reaching terminal velocity

Skydiver in freefall reaching terminal velocity

The skydiver initially accelerates downward due to the force of weight. The upward force of air resistance increases as they fall until eventually it equals the weight force and terminal velocity is reached

• At the instant the skydiver steps out of the plane, the support force of the plane is no longer acting on the skydiver, but they are not yet falling, so the only force exerted them is the weight force

  • There is a downward acting resultant force on the skydiver

  • The resultant force is equal to the weight force

  • The skydiver accelerates downward at maximum acceleration

• As the skydiver begins to fall, the force of air resistance is very small because the skydiver's speed is small

  • There is a downward acting resultant force on the skydiver

  • The resultant force is equal to the weight force minus the force of air resistance

  • The skydiver accelerates downward but the acceleration decreases

• As the skydiver accelerates, their speed increases, so the force of air resistance increases

  • There is a downward acting resultant force on the skydiver

  • The resultant force is equal to the weight force minus the force of air resistance

  • The skydiver accelerates downward but the acceleration continues to decrease

• As the skydiver's acceleration decreases, their speed increases at a slower and slower rate

  • Eventually, the skydiver reaches a speed at which the force of air resistance is equal to the force of weight

  • The forces are balanced, so the resultant force is zero

  • The skydiver no longer accelerates and a constant velocity is reached

    • This is terminal velocity