Lesson 7 Grades 6–8
Parachutes and landing energy
- Timeabout 60 minutes
- WorksheetW7 Parachute drop test
- Rocket BuilderWhich parachute? card
Worksheets (PDF) Open Rocket Builder
Standards
| Code | In plain words |
|---|---|
| MS-PS3-1 | Graph data to show how kinetic energy depends on mass and on speed. |
| MS-PS2-2 | Balanced forces (drag = weight) mean a steady speed. |
| MS-ETS1-3 | Analyze test data to find the best design features. |
| 7.RP.A.2 (math) | Proportional relationships: drift = time × wind speed. |
Practice: analyzing and interpreting data. Crosscutting concept: scale, proportion and quantity.
I can…
- I can explain terminal speed: a falling object stops speeding up when drag equals weight.
- I can calculate descent rate (height ÷ time) from a drop test.
- I can use a graph to show that kinetic energy grows faster than speed, and explain why a rocket must land slowly.
Words to know
- Descent rate falling speed, m/s. Terminal speed: the steady speed when drag balances weight.
- Kinetic energy KE = ½ × mass × speed². Double the speed, four times the energy.
- Drift how far the wind carries the rocket sideways while it comes down.
Materials
Plastic bags, string, tape, identical washers, stopwatches, a tape measure, a 2–3 m drop spot (an adult drops), W7. Optional: a paper or plastic streamer.
Steps
1Teach10 min
Read aloudAs something falls, drag grows with speed until it equals the weight. Then the forces balance and the speed stops changing: terminal speed. A parachute makes a lot of drag, so the balance comes at a slow speed. Rocket Builder picks the smallest standard chute (12, 15, 18, 24… inches) that brings your rocket down at about 4.5 m/s or less. Too big a chute hangs in the air longer and drifts farther.
2Drop test25 min
- Make 20, 30 and 40 cm parachutes with 30 cm lines and the same washers.
- An adult drops each from the same height; time 3 trials each; also the washers alone (and a streamer, if you made one).
- Mean time and descent rate (height ÷ mean time) for each. Graph canopy size vs time.
3Landing energy15 min
On W7, fill the kinetic energy table for an 80 g (0.08 kg) rocket landing at 2, 4, 8 and 16 m/s, and plot KE against speed. Then for 40, 80 and 160 g at 4 m/s, plot KE against mass. Which graph is a straight line?
4Rocket Builder5 min
Find Which parachute?: size and descent speed. Time down = altitude ÷ descent speed; drift in a 4.5 m/s breeze = time × 4.5.
5Wrap up5 min
Why does landing at 16 m/s break a rocket when 4 m/s doesn't?
Check for understanding
- A parachute falls 3 m in 1.5 s. Descent rate?
- At terminal speed, which two forces are balanced?
- Landing speed doubles from 4 to 8 m/s. What happens to the kinetic energy?
- From 100 m at 4 m/s in a 4.5 m/s wind: how far does it drift?
Answer key
- 2 m/s.
- Drag (up) and weight (down).
- It becomes 4 times bigger.
- 100 ÷ 4 = 25 s; 25 × 4.5 ≈ 113 m.
Teacher notes
- KE table answers (0.08 kg): 2 m/s 0.16 J; 4 m/s 0.64 J; 8 m/s 2.56 J; 16 m/s 10.24 J (a curve). Mass at 4 m/s: 40 g 0.32 J; 80 g 0.64 J; 160 g 1.28 J (a straight line). A landing at 4.5 m/s is like jumping off a step about 1 m high; 16 m/s is like falling about 13 m, off a four-storey roof.
- Extension: descent speed = √(2mg ÷ (1.2 × Cd × area)), Cd ≈ 0.75. A 76 g rocket under a 15-inch chute: ≈ 3.8 m/s, the app's number. Doubling the chute's width halves the speed.
- 12+ track: get the parachute size the app says (or make one), and practise folding it: in half twice, lines wrapped loosely, rolled to slide easily into the body tube. Flame-resistant wadding goes below it on launch day.
- Further resources: Apogee Components' free lesson The Optimum Descent Challenge (apogeerockets.com/downloads/PDFs/58-4.pdf).
- Parachute or streamer: the launch simulator flies the rocket with either, showing descent speed and drift. Its descent graph is a clean terminal-speed curve for the KE discussion.