Course: Combined Science + Separate Physics | Tier: Foundation + Higher | Linked: Terminal velocity notes · Resultant forces
✏️ You need: 1 sheet of A4 graph paper (stick it into your book afterwards), a sharp pencil, a ruler and a calculator. Draw the graph before opening any answers.
📌 KEY DEFINITIONS – learn them word for word
Weight is the force of gravity pulling the skydiver down. It stays the same the whole time.
Air resistance pushes up against the skydiver. It gets bigger as she goes faster.
Terminal velocity: the top (constant) speed of a falling object, reached when air resistance = weight, so the resultant force is zero.
The jump 🪂
A skydiver jumps out of a plane. She falls faster and faster until she reaches a steady speed. At 16 seconds she opens her parachute. She slows down quickly, then falls at a new, slow, steady speed until she lands safely at 30 seconds.
| Time (s) | 0 | 2 | 4 | 6 | 8 | 10 | 12 | 14 |
| Speed (m/s) | 0 | 18 | 32 | 42 | 48 | 50 | 50 | 50 |
| Time (s) | 16 | 18 | 20 | 22 | 24 | 26 | 28 | 30 |
| Speed (m/s) | 50 | 20 | 10 | 6 | 5 | 5 | 5 | 5 |
How to draw the graph
- Turn your graph paper landscape. Draw the axes with a ruler, about 2 cm in from the bottom and left edges. Time (s) along the bottom, Speed (m/s) up the side.
- 📏 Time scale: 1 big square = 2 s. Number the big lines 0, 2, 4, 6 … up to 32. The axis is 16 cm long.
- 📏 Speed scale: 1 big square = 5 m/s. Number the big lines 0, 5, 10, 15 … up to 55. Each small square = 1 m/s, so 18 m/s is 3 big squares + 3 small squares.
- Plot all 16 points as small crosses.
- Join the crosses with a smooth curve drawn freehand – not with a ruler. Use a ruler only for the flat parts.
- She lands at 30 s: draw a straight line down to 0 m/s at 30 s.
- Label the parts: A speeding up (0–10 s), B first terminal velocity (10–16 s), C parachute opens, slowing down (16–24 s), D new terminal velocity (24–30 s), E lands.
🔍 See examples of the skydiver graph · Forces key diagrams
Part 1: Read your graph
Q1 What is her first terminal velocity? What does the flat line tell you?
Show answer
50 m/s. The flat line means her speed is not changing – she is falling at a constant speed.
Q2 What is her terminal velocity with the parachute open?
Show answer
5 m/s – much slower, so she can land safely.
Q3 Work out her acceleration in the first 2 seconds. (Acceleration = change in speed ÷ time.)
Show answer
Change in speed = 18 − 0 = 18 m/s. Time = 2 s.
Acceleration = 18 ÷ 2 = 9 m/s²
Q4 Work out her deceleration from 16 s to 18 s, just after the parachute opens.
Show answer
Change in speed = 50 − 20 = 30 m/s. Time = 2 s.
Deceleration = 30 ÷ 2 = 15 m/s²
Q5 In part C the line goes down. Is she going back up into the sky?
Show answer
No! This is a speed–time graph. The line going down means her speed is getting smaller – she is still falling, just more slowly.
Part 2: Draw the forces ⬆️⬇️
Under your graph, draw a stick-person skydiver for parts A, B, C and D. On each one draw two arrows with a ruler: weight pointing down and air resistance pointing up. Longer arrow = bigger force. Weight is the same length every time.
Check your arrows
| Part | Arrows | What happens |
|---|---|---|
| A (just jumped) | Weight arrow longer than air resistance | Speeds up |
| B (terminal velocity) | Both arrows the same length | Constant speed |
| C (parachute just opened) | Air resistance arrow much longer than weight | Slows down |
| D (new terminal velocity) | Both arrows the same length again | Constant, slower speed |
Part 3: Explain the graph
Use these words: weight, air resistance, bigger than, equal to, speeds up, slows down, constant speed.
Q6 Why does she speed up when she first jumps?
Show answer
Her weight is bigger than the air resistance, so there is a resultant force downwards and she speeds up.
Q7 Why does the curve get less steep as she falls?
Show answer
As she goes faster, the air resistance gets bigger. The resultant force gets smaller, so she speeds up more slowly.
Q8 Why does she fall at a constant speed in part B?
Show answer
The air resistance is equal to her weight. The resultant force is zero, so she falls at a constant speed – her terminal velocity.
Q9 Why does she slow down when the parachute opens?
Show answer
The parachute has a big area, so the air resistance suddenly gets much bigger than her weight. The resultant force is upwards, so she slows down.
Q10 Why doesn’t she keep slowing down until she stops in mid-air?
Show answer
As she slows down, the air resistance gets smaller. When it is equal to her weight again, the resultant force is zero and she falls at a new, slower terminal velocity of 5 m/s.
⚠️ Where students lose marks
- Saying gravity gets weaker or stronger. Her weight stays the same – it is the air resistance that changes.
- Saying “the forces are balanced so she stops”. Balanced forces mean constant speed, not stopped.
- Thinking she goes up when the parachute opens. She keeps falling – just more slowly.
- Joining the points with a ruler. The speeding-up and slowing-down parts are curves.
Next: Distance–time graph activity · Speed–time graph activity · Terminal velocity notes
