AQA GCSE Physics · Forces
Acceleration required practical
Investigate the effect of varying the force on the acceleration of an object of constant mass.
A trolley is pulled along a bench by a falling mass. Light gates measure its acceleration. More force gives more acceleration: a is directly proportional to F, as Newton’s second law says.
Equipment
- Trolley on a bench, with a card (interrupter) on top
- Pulley clamped to the end of the bench
- String and a mass hanger with 100 g slotted masses
- Two light gates and a data logger (or ruler, tape and stopwatch)
- Balance
Variables
- Independent you change
- Force pulling the trolley (weight of the hanging masses)
- Dependent you measure
- Acceleration of the trolley
- Control you keep the same
- Total mass of trolley + masses (move masses from trolley to hanger)
- Same distance between light gates
- Same surface
Method
- 1
Attach the trolley to a string that passes over a pulley to a mass hanger.
- 2
Set up two light gates along the bench, connected to a data logger.
- 3
Start with all the masses on the trolley. Move one mass to the hanger and release the trolley from the same place.
- 4
Record the acceleration calculated by the data logger.
- 5
Move another mass from the trolley to the hanger, so the total mass stays the same, and repeat.
- 6
Plot acceleration against force.
Worked example
Total mass of trolley and masses kept at 1.0 kg.
| Force (N) | Acceleration (m/s²) |
|---|---|
| 0.2 | 0.19 |
| 0.4 | 0.41 |
| 0.6 | 0.58 |
| 0.8 | 0.81 |
| 1.0 | 0.99 |
Working
Light gates: a = (v − u) ÷ t, from the speeds at each gate and the time between them
F = m × a, so m = F ÷ a = 1.0 ÷ 0.99 ≈ 1.0 kg
Conclusion
The graph is a straight line through the origin, so acceleration is directly proportional to the resultant force when mass is constant. The gradient is 1 ÷ mass, which matches F = ma for a 1.0 kg system.
Risks
- Trolley could fall off the benchPut a buffer or stop at the end of the bench.
- Masses could fall on feetKeep feet clear of the hanger and don’t use too much mass.
Common mistakes
- Adding new masses to the hanger instead of moving them from the trolley. That changes the total mass too.
- Using a stopwatch over a short distance. Reaction time causes big errors; light gates are much better.
- Forgetting that friction acts on the trolley, so the resultant force is a bit less than the weight on the hanger.
Better results
- Use light gates instead of a stopwatch to reduce timing errors.
- Tilt the bench slightly so the trolley just rolls on its own, compensating for friction.
- Repeat each force and calculate a mean acceleration.
Launching November 2026
7 exam questions on this practical.
Practise the method, the variables, the maths and what the results mean, then revise the Forces flashcards. It opens to students soon: join the waitlist and we’ll email you once, when it does.