Terminal Velocity (Oxford AQA IGCSE Physics)

Terminal Velocity

• Objects falling through fluids will experience two forces

  • Weight

  • Drag

• At the moment the object is released, the only force acting on it is weight

  • It has not yet begun to move through the fluid

  • It is not being supported by any surface

• The resultant force causes the object to accelerate

• As the object accelerates, the drag force takes effect

  • The object collides with the particles in the fluid

• The drag force increases with speed

  • As the object accelerates, speed increases so the drag force increases

  • The greater the speed of the object, the greater the drag force

• Eventually, the drag force becomes balanced with the weight force

  • There is no resultant force

  • The object falls at a constant velocity

  • This is terminal velocity

Parachutes

• Parachutes can be used to reduce the terminal velocity of an object allowing it to land safely

Forces acting on a skydiver

• When a skydiver jumps out of a plane, initially the only force acting on them is weight

  • The resultant force acts in the downward direction

  • The skydiver accelerates

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

  • The resultant force acts in the downward direction with a smaller magnitude

  • The skydiver continues to accelerate but at a slower rate

• Air resistance increases until it is equal to the weight

  • The forces are balanced

  • There is no resultant force

  • Terminal velocity is reached

• The parachute is deployed increasing the surface area of the skydiver

  • The parachute collides with many more air particles

  • Air resistance increases greatly

• The force of air resistance is now greater than the force of weight

  • The resultant force acts in the upward direction

  • The skydiver continues falling in the downward direction

  • The skydiver is decelerating

• As the skydiver decelerates, their speed decreases

  • Therefore air resistance decreases

  • Therefore the resultant force decreases

• Air resistance decreases until it is equal to the weight

  • The forces are balanced

  • There is no resultant force

  • A new slower terminal velocity is reached

Velocity-time graph of a skydiver