Lesson focus: A falling object changes speed as dragA force that acts against an object moving through air or water, slowing it down; air resistance is one kind of drag. changes until forceA push or a pull, measured in newtons (N). balance.
Explain accelerationHow quickly something speeds up, slows down or changes direction., parachute opening and terminal speedThe top speed a falling object reaches when air resistance balances its weight. from force diagrams.
Build on earlier learning
Drag forces and frictionApply drag direction and size to a moving object.
Practical
Parachutes and air resistance
- Drop a load with parachutes of different area from the same height.
- Time each fall three times and calculate the mean.
- Keep the load, height and parachute material the same.
Record: A table and a graph of canopy area against mean fall time.
Falling with air resistance
Air resistance grows as the skydiver speeds up. When it balances the weight, the speed stops changing: terminal velocity. Opening the parachute makes the air resistance much bigger.
Controls
You will be successful when you can…
- Identify weight and drag.
- Explain initial acceleration.
- Define terminal speed.
- Explain deceleration after opening.
Words that carry the science
- weight
- Gravitational force on an object.
- air resistance
- Drag force from motion relative to air.
- terminal speed
- Constant speed reached when drag balances weight.
- acceleration
- Rate of change of velocity.
- deceleration
- Acceleration that reduces speed.
Follow the resultant through a changing descent
01At release
Speed and drag are initially small, so weightThe force of gravity on an object, measured in newtons (N); it changes on other planets, while the mass stays the same. is larger and the object accelerates downward.
02First terminal speed
As speed rises, drag rises until it equals weight. Resultant becomes zero and speed becomes constant.
03Parachute transition
Opening suddenly increases area and drag above weight. The person slows; drag then falls with speed until it again balances weight at a lower terminal speedThe top speed a falling object reaches when air resistance balances its weight..
In simple steps: (1) the parachute opens and is much bigger, so air resistance (drag) jumps up. (2) Now drag is bigger than weight, so the person slows down. (3) As they slow down, drag gets smaller. (4) When drag equals weight again, the forces are balanced and the person falls at a steady, lower speed.
Explain the opening sequence
A parachute opens during steady descent.
- Before opening, drag equals weight.
- Opening increases area, so drag becomes larger than weight.
- Upward resultant causes downward speed to decrease.
- As speed falls, drag falls until equal to weight at new lower terminal speed.
How to make the reasoning visible: Do not jump directly from opening to balanced forces.
Descent stages
Track force size and motion.
| Stage | Weight | Drag | Motion |
|---|---|---|---|
| Just released | Larger | Small | Speeds up downward |
| Fast fall | Same | Increasing | Acceleration decreases |
| First terminal | Equal | Equal | Constant high speed |
| After parachute opens | Smaller than drag | Suddenly large | Slows downward |
| New terminal | Equal | Equal | Constant lower speed |
Why does drag fall after opening even though area stays large?
What is resultant at terminal speed?
Use the table. When a skydiver is just released, why do they speed up?
Check your understanding
Answer from memory, then check against the suggested answer.
What is weight?
What is air resistance?
What is terminal speed?
What does air resistance depend on?
In which direction does weight act?
A heavier person uses the same parachute. Predict the new terminal speed.
Why does “upward resultant” not mean upward motion?
Why does opening a parachute make the skydiver slow down?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A skydiver is falling at a steady speed. Then they open their parachute. Answer the parts to explain what happens.
What happens to air resistance (drag) when the parachute opens?
(1)Which force is now bigger: drag or weight?
(1)So what happens to the skydiver’s speed?
(1)As the skydiver slows down, what happens to drag?
(1)What happens when drag equals weight again?
(1)Total for this question: 5 marks
Command word: Follow the steps in section 03 in order. One step = one mark.