Physics - Free Fall
OCR A-Level Physics 2022
Air resistance and drag
What is the difference between air resistance and drag?
Drag is applicable to fluids other than air.
The forces-resultant-result method
What are the three questions that you should ask at each stage of free fall?
- What are the forces?
- What is the resultant force?
- What is happening?
What’s an easy way to remember the three questions you ask at each stage of free fall?
Forces, resultant, result.
Stages of a skydive
A skydiver has just left a plane. What are the 5 stages of their journey?
- Leaving the plane
- Speeding up
- Terminal velocity
- Parachute opening
- Terminal velocity
Following the forces, resultant, result pattern, what’s happening when a skydiver leaves a plane?
- _ _ Forces _ _ : The only force acting is weight downwards
- _ _ Resultant _ _ : There’s a large resultant force downwards
- _ _ Result _ _ : Accelerates downwards at $9.81ms^{-2}$
Following the forces, resultant, result pattern, what’s happening when a skydiver is speeding up after leaving the plane?
- _ _ Forces _ _ : Weight downwards and drag acting upwards
- _ _ Resultant _ _ : Resultant force decreases, though still downwards
- _ _ Result _ _ : Acceleration decreases
Following the forces, resultant, result pattern, what’s happening when a skydiver reaches terminal velocity for the first time?
- _ _ Forces _ _ : Drag is equal in magnitude to weight
- _ _ Resultant _ _ : Resultant force is zero.
- _ _ Result _ _ : Terminal velocity, zero acceleration
Following the forces, resultant, result pattern, what’s happening when a skydiver’s parachute opens?
- _ _ Forces _ _ : Drag increases as parachute opens
- _ _ Resultant _ _ : Large resultant force upwards
- _ _ Result _ _ : Speed decreases, large deceleration
Following the forces, resultant, result pattern, what’s happening when a skydiver reaches terminal velocity for the second time?
- _ _ Forces _ _ : Drag decreases as speed decreases
- _ _ Resultant _ _ : Resultant force is zero.
- _ _ Result _ _ : Terminal velocity, zero acceleration.
Drag and speed
If you have a skydiver with no parachute and a skydiver with an open parachute, which is experiencing the most drag?
The skydiver without a parachute.
Why does a skydiver without a parachute experience more drag than one with a parachute?
- Drag increases with speed
- Skydiver without a parachute is moving faster