Welcome! Aid agencies drop food and medicine by parachute. Too slow and the wind blows it off course. Too fast and it smashes. Today you’ll be a parachute test engineer. You’ll drop cupcake cases, stack more and more together, and time how long they take to fall. Then you’ll explain your results using forces.
🔑 Key words for today
- Weight – the force of gravity pulling an object down. Measured in newtons (N).
- Air resistance – a force from the air that pushes against a moving object.
- Terminal velocity – the top speed of a falling object, when air resistance equals weight.
- Independent variable – the thing you change.
- Dependent variable – the thing you measure.
- Control variable – something you keep the same to make it a fair test.
- Anomaly – a result that doesn’t fit the pattern.
Before you start
- You need: 5 identical paper cupcake cases, a metre rule or tape measure, a stopwatch (a phone is fine), a partner, your exercise book, a pen and a calculator.
- No equipment? You can still do the whole lesson using the class results in Step 4.
- Write the title and date: Falling cupcake cases – Parachute Test Lab.
- ⭐ Core = everyone does this (about 45 minutes). 🚀 Stretch = extra challenge if you finish.
- Write your answer first, then tap Show answer. Correct mistakes in a different colour.
- Copy the blue 📝 boxes into your book – they are your revision notes.
📝 Copy into your book
By the end of this lesson I will be able to:
1. explain how weight and air resistance affect a falling object
2. plan a fair test and name the independent, dependent and control variables
3. (🚀) calculate a mean and uncertainty, and evaluate my method.
⭐ Step 1: Starter (5 minutes)
Hold a flat cupcake case in one hand and a cupcake case scrunched into a tight ball in the other. They have exactly the same mass. Drop them together from the same height. Which lands first, and why?
Show answer
The scrunched ball lands first. Both have the same weight, but the open case has a bigger surface area, so it has more air resistance. That slows it down. Parachutes work in exactly the same way!
📝 Copy into your book
Air resistance is BIGGER when an object has a bigger surface area or moves FASTER.
⭐ Step 2: Read and write (8 minutes)
Copy these three questions. Then read the text and answer them.
- What two forces act on a falling cupcake case?
- What is terminal velocity?
- Why should a stack of cases fall faster than one case?
📖 Read: Why do things fall at different speeds?
Two forces. A falling cupcake case has two forces on it. Weight pulls it down. Air resistance pushes up against it. When you let go, the case is not moving yet, so there is no air resistance. The case speeds up.
Terminal velocity. As the case gets faster, the air resistance gets bigger. Soon the air resistance is equal to the weight. The forces are balanced, so the resultant force is zero. The case stops speeding up and falls at a steady top speed. This is its terminal velocity.
Stacking cases. Stacked cases fit inside each other, so the stack has the same shape and area as one case – but more weight. It has to fall faster before the air resistance is big enough to balance that weight. So a stack has a higher terminal velocity and reaches the ground sooner.
Show answers
(a) Weight (down) and air resistance (up).
(b) The steady top speed of a falling object, reached when air resistance equals weight.
(c) A stack has more weight but the same shape, so it must fall faster before air resistance balances the weight – it has a higher terminal velocity.
📝 Copy into your book
Falling object: weight DOWN, air resistance UP.
Faster → MORE air resistance → air resistance = weight → resultant force = 0 → TERMINAL VELOCITY.
More weight, same shape → HIGHER terminal velocity → SHORTER fall time.
⭐ Step 3: Plan a fair test (8 minutes)
👀 Watch me first
Question: does the size of a parachute affect how long it takes to fall?
Independent variable (what I change): the size of the parachute
Dependent variable (what I measure): the time to fall
Control variables (what I keep the same): the drop height, the mass hanging from the parachute, the material
⭐ Now you try: for today’s investigation – how does the number of cupcake cases affect the time taken to fall? – write down the independent variable, the dependent variable and three control variables.
Show answer
Independent: the number of cupcake cases
Dependent: the time taken to fall
Control (any three): the drop height; the type and size of cupcake case; dropping it the same way up; the same person timing; no draughts (windows closed, fans off).
⭐ Write a hypothesis: “I think that as the number of cupcake cases increases, the time taken to fall will ______ because ______.”
Show a model hypothesis
I think that as the number of cupcake cases increases, the time taken to fall will decrease because the weight increases but the shape stays the same, so the stack reaches a higher terminal velocity.
⚠️ Stay safe
Never stand on a chair, stool or desk. Drop the cases from a height you can reach while standing on the floor, such as a mark on the wall at 2.0 m. Keep the floor clear so nobody trips while watching the cases land.
📝 Copy into your book
INDEPENDENT variable = what I CHANGE.
DEPENDENT variable = what I MEASURE.
CONTROL variables = what I keep the SAME, to make it a FAIR TEST.
⭐ Step 4: Main task – Parachute Test Lab (15 minutes)
Method – work with a partner:
- Measure and mark a drop height of 2.0 m on a wall.
- Hold one cupcake case open side up, with its base level with the mark.
- Say “3, 2, 1, drop”. Your partner starts the stopwatch as you let go and stops it when the case hits the floor.
- Record the time. Repeat twice more, so you have three times.
- Stack a second case inside the first and repeat. Keep going up to five cases.
Draw a results table like the one below. No equipment? Use these class results.
| Number of cases | Time 1 (s) | Time 2 (s) | Time 3 (s) | Mean time (s) |
|---|---|---|---|---|
| 1 | 1.92 | 1.88 | 1.95 | |
| 2 | 1.40 | 1.45 | 1.38 | |
| 3 | 1.18 | 1.21 | 1.52 | |
| 4 | 1.02 | 1.05 | 1.00 | |
| 5 | 0.93 | 0.90 | 0.92 |
⭐ Core: one result is an anomaly. Find it. Then calculate the mean time for each number of cases, to 2 decimal places. Leave the anomaly out of its mean.
Show answer
Anomaly: 1.52 s for 3 cases – it’s much longer than the other two.
1 case: (1.92 + 1.88 + 1.95) ÷ 3 = 1.92 s
2 cases: (1.40 + 1.45 + 1.38) ÷ 3 = 1.41 s
3 cases: (1.18 + 1.21) ÷ 2 = 1.20 s (anomaly left out)
4 cases: (1.02 + 1.05 + 1.00) ÷ 3 = 1.02 s
5 cases: (0.93 + 0.90 + 0.92) ÷ 3 = 0.92 s
⭐ Core: plot a graph of mean time (y-axis) against number of cases (x-axis). Then write a conclusion.
✏️ Sentence starters
As the number of cases increases, the time taken to fall ______.
One case took ______ s, but five cases took only ______ s.
This is because the weight ______, but the shape stays the same, so ______.
My hypothesis was ______.
Show a model conclusion
As the number of cases increases, the time taken to fall decreases. One case took 1.92 s, but five cases took only 0.92 s. The time drops by less each time a case is added. This is because the weight increases, but the shape stays the same, so the stack must fall faster before air resistance balances its weight – it has a higher terminal velocity. My hypothesis was correct.
🚀 Stretch 1 – uncertainty: the uncertainty in a mean is about half the range of the repeat readings. Calculate the uncertainty for 4 cases.
Show answer
Range = 1.05 − 1.00 = 0.05 s
Uncertainty = 0.05 ÷ 2 = 0.025 s
Mean time = 1.02 ± 0.03 s
🚀 Stretch 2 – evaluate: the biggest problem with this method is the person timing it. Explain why, and suggest two ways to improve the investigation.
Show answer
The person’s reaction time when starting and stopping the stopwatch causes random error. With times of about 1 s, a reaction time of about 0.2 s is a big part of the measurement.
Improvements (any two): drop from a greater height so the times are longer; film the drop on a phone with a timer or slow motion; use light gates and a data logger; take more repeats and calculate a mean.
Step 5: Exam practice (10 minutes)
⭐ Q1 (3 marks) A student investigates how the number of cupcake cases affects the time taken to fall. Name the independent variable, the dependent variable and one control variable.
Show model answer
Independent: number of cupcake cases (1)
Dependent: time taken to fall (1)
Control: drop height / same type of case / same person timing (1)
⭐ Q2 (3 marks) Explain why a stack of five cupcake cases reaches the ground sooner than a single case.
✏️ Start with: “The stack has more weight but…” then “so it must fall faster before…” then “so its terminal velocity…”
Show model answer
The stack has more weight but the same shape / surface area (1), so it must fall faster before air resistance becomes equal to its weight (1), so its terminal velocity is higher and it reaches the ground sooner (1).
🚀 Q3 (2 marks) The student’s times for one case were 1.92 s, 1.88 s and 1.95 s. Suggest why the three times are different, and how this affects the reliability of the results.
Show model answer
The student’s reaction time is different each time they start and stop the stopwatch – this is random error (1). Repeating and calculating a mean reduces the effect of random error, making the results more precise (1).
✅ Core score out of 6 (Q1–Q2). Stretch: out of 8.
⭐ Step 6: Exit ticket (5 minutes)
- A falling object reaches terminal velocity when…
- To make an investigation a fair test, I need to…
- One thing I’m still not sure about is…
🎉 Well done – lesson complete! Your 📝 boxes are your revision notes. Want more? Try the Terminal velocity questions, the Skydive Challenge lesson or Working scientifically.
