Physics With Kate
Empowering Girls in Physics
Spec-aligned revision resources, group courses, and 1:1 tutoring for GCSE and A Level Physics — built by an experienced teacher and examiner.
Edexcel International GCSE Physics · Section 1 Forces and motion
Motion of Everyday Objects — Required Practical
In this lesson you'll learn to: describe how to investigate the motion of everyday objects
such as tennis balls and toy cars, use your results to calculate the
acceleration — and from a falling ball, the gravitational field strength g
— and evaluate the method.
▶
Prefer to watch? Scroll to the bottom for the video on this practical
▶
A video walkthrough is coming soon — it will appear at the bottom of this page
▶
Start here — run the practical
Don't read anything yet. Drop a ball through a light gate from five heights and watch the results table and the graph fill in as you go. Try a steel ball and a ping-pong ball, then give one a push and see what it does to your answer. The stop clock tab is the method on page 6 of your workbook. Then put the method in order and spot what went wrong for five students.
1 · Choose the drop height s (bottom of the ball to the light gate)
| height s / m | speed at gate v / m/s | v² / m²/s² | a = v² ÷ 2s / m/s² |
|---|
Why v² = u² + 2as? The ball starts from rest, so u = 0 and the equation becomes v² = 2as. Rearrange: a = v² ÷ 2s. The light gate and data logger give you v; the tape measure gives you s.
1 · Choose the drop height s (bottom of the ball to the floor)
Each press times the drop three times
| s / m | t₁ / s | t₂ / s | t₃ / s | mean t / s | t² / s² | a = 2s ÷ t² / m/s² |
|---|
Where a = 2s ÷ t² comes from — using only iGCSE equations. Average speed = s ÷ t. It starts from rest and speeds up steadily, so its final speed is twice the average: v = 2s ÷ t. Then a = (v − u) ÷ t = (2s ÷ t − 0) ÷ t = 2s ÷ t². On a graph of s against t², the gradient is a ÷ 2, so a = 2 × gradient.
Click the steps in the right order
Your method
Start with the step you would do first.
right first time 0 / 0
Physics With Kate · physicswithkate.com — Edexcel International GCSE Physics
▲ The falls run in slow motion. The speeds and times are the real ones.
Same acceleration from every height — and it's about 9.8 m/s².
The notes below give you the method, the equation, the graph and the evaluation points — everything a "describe an experiment" question asks for.
✎
Revision notes
🎯 Aim
Investigate the motion of everyday objects, such as toy cars and tennis balls, and use the results to calculate the acceleration. For a dropped ball, that acceleration is the gravitational field strength, g.
Apparatus
- a tennis ball (or a toy car and a ramp)
- a tape measure or metre rule
- a light gate connected to a data logger — or a stop clock
- a clamp and stand to hold the light gate
Method 1 — light gate and data logger
- Clamp a light gate near the floor and connect it to a data logger.
- Measure the height s from the bottom of the ball to the light gate.
- Let go of the ball from rest — don't push it — so that u = 0.
- Read the speed v of the ball through the gate from the data logger.
- Calculate the acceleration: a = v² ÷ 2s.
- Repeat from 1.8 m, 1.6 m, 1.4 m and 1.2 m, three times each, and take a mean.
Where a = v² ÷ 2s comes from. Start from v² = u² + 2as. The ball starts from rest, so u = 0 and v² = 2as. Divide both sides by 2s: a = v² ÷ 2s.
How the light gate gets v. The ball blocks the beam as it passes. The data logger measures how long the beam is blocked and divides the width of the ball by that time: speed = distance ÷ time.
Method 2 — stop clock (workbook page 6)
- Measure the height s from the ground to the bottom of the ball, starting at 2.0 m.
- Drop the ball from rest, making sure it is not pushed.
- Measure the time t from letting go to the ball hitting the ground, with a stop clock. Repeat three times and take a mean.
- Calculate the acceleration: a = 2s ÷ t².
- Repeat for 1.8 m, 1.6 m, 1.4 m and 1.2 m.
Where a = 2s ÷ t² comes from. Average speed = s ÷ t. A ball speeding up steadily from rest reaches a final speed of twice its average speed, so v = 2s ÷ t. Then a = (v − u) ÷ t = (2s ÷ t) ÷ t = 2s ÷ t².
Variables
| Variable | In this practical |
|---|---|
| Independent — what you change | the drop height s |
| Dependent — what you measure | the speed v at the light gate (or the time t) |
| Control — what you keep the same | the same ball, released from rest, the same way each time |
Example results — light gate
| height s / m | speed v / m/s | v² / m²/s² | a = v² ÷ 2s / m/s² |
|---|---|---|---|
| 2.0 | 6.20 | 38.4 | 9.6 |
| 1.8 | 5.89 | 34.7 | 9.6 |
| 1.6 | 5.57 | 31.0 | 9.7 |
| 1.4 | 5.20 | 27.0 | 9.7 |
| 1.2 | 4.83 | 23.3 | 9.7 |
The graph
Plot v² (y-axis) against s (x-axis). Because v² = 2as, you get a straight line through the origin with gradient = 2a, so a = gradient ÷ 2.
With a stop clock, plot s (y-axis) against t² (x-axis). That is also a straight line through the origin, with gradient = a ÷ 2, so a = 2 × gradient.
Conclusion
⭐ Model conclusion
The acceleration is the same for each height, with a value of approximately 9.7 m/s², which is the gravitational field strength.
Evaluation
| What to do | Why | |
|---|---|---|
| Precaution | Let go of the ball from rest — don't push it | a = v² ÷ 2s only works if u = 0. A push makes a too big. |
| Precaution | Measure s from the bottom of the ball, at eye level | That is the distance it actually falls. Eye level avoids parallax error. |
| Improvement | Use a more streamlined, dense object (a steel ball) | Reduces air resistance, so a is closer to g. |
| Improvement | Use a light gate instead of a stop clock | A 2 m fall takes about 0.6 s; reaction time (about 0.2 s) is a big share of that. |
| Improvement | Repeat each height and take a mean | Reduces the effect of random error. |
Toy car down a ramp
The same practical works for a toy car rolling down a ramp, which past papers have used. Release the car from rest at a measured distance s up the ramp, measure its speed v with a light gate at the bottom, and calculate a = v² ÷ 2s. The acceleration is the same from every distance — a constant acceleration — but much less than 9.8 m/s², because only part of the car's weight pulls it down the slope.
⚠ Safety
Keep feet and hands clear of where the ball or car lands. Clamp the stand firmly so it can't topple, and don't stand on a chair to reach a bigger height.
How to write it in the exam
"Describe an experiment…" — hit these four every time
what you measure, and with what →
release from rest & repeat →
the equation that gives a
s with a tape measure; v with a light gate (or t with a stop clock) u = 0, several heights, take a mean a = v² ÷ 2s or a = 2s ÷ t²
A ball is dropped from rest through a height of 1.5 m. A light gate measures its speed as 5.4 m/s. Calculate its acceleration.
v² = u² + 2as with u = 0 · a = v² ÷ 2s = 5.4² ÷ (2 × 1.5) = 29.16 ÷ 3.0 = 9.7 m/s²
A tennis ball falls 2.0 m in a mean time of 0.64 s. Calculate its acceleration.
a = 2s ÷ t² = (2 × 2.0) ÷ 0.64² = 4.0 ÷ 0.41 = 9.8 m/s²
A student's values of acceleration are all bigger than 9.8 m/s². Suggest a reason.
The ball was pushed as it was released, so its starting speed was not zero and the speed at the light gate was bigger than it should be.
Suggest one improvement to the stop clock method, and explain it.
Use a light gate and data logger instead, because the fall only takes about 0.6 s and human reaction time is a large fraction of that.
✅ Check your answer has
What you measure and what with · release from rest · repeat for several heights and take a mean · the equation you use to get a · a conclusion that names g, about 9.8 m/s².
📘 Now do it in your workbook
Draw the set-up, fill the gaps in the method, complete the results table and the graph, then write the conclusion and evaluation.
Edexcel iGCSE Forces and Motion Workbook · page 6✅ Can you do it? Tick as you go
0% complete🎉 Nice work! You've ticked off every objective for this practical.
▶
Prefer to watch? Here's the whole thing
Video walkthrough — coming soon
The whole practical, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it.
The whole practical, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it. The video is on its way.
🎬
Video coming soon
The walkthrough for this practical is being filmed and will appear right here. Until then, the notes and the free workbook page above cover every mark.
Now put it into practice
Page 6 of the Forces and Motion workbook is free: draw the set-up, complete the method, the results, the graph, the conclusion and the evaluation. The full book covers the whole topic with worked answers.
Proud member · Accredited · Trusted partners
© 2026 Physics With Kate · All rights reserved