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Physics required practicals

Acceleration, force and mass

AQA 4.5 · RP7

GCSE Physics (8463) · Required practical 7 — method, variables, the marks examiners report students losing.

Board and spec code confirmed against AQA 8463 · registry checked 2026-07-17How this checking works

Investigate how the acceleration of an object depends on the resultant force on it (at constant mass) and on its mass (at constant force), verifying F = m x a.

Apparatus

  • Dynamics trolley on a runway or linear air track
  • Light gates and a data logger (or ticker tape and timer) to measure acceleration
  • String over a pulley at the end of the bench, with a mass hanger and slotted masses
  • Extra masses to load onto the trolley, and a balance

Method

  1. 1Set up the trolley on the runway with a string over a pulley to a hanging mass; tilt the runway slightly to compensate for friction (until a tapped trolley moves at steady speed).
  2. 2To investigate force: keep the total mass of the system constant by moving masses from the trolley onto the hanger; measure the acceleration with the light gates for each force.
  3. 3To investigate mass: keep the hanging mass (the force) constant and add masses to the trolley; measure the acceleration each time.
  4. 4Record the acceleration for each force and for each mass.
  5. 5Plot acceleration against force, and acceleration against mass (or against 1 / mass).

Variables

Independent

Resultant force (part a) or mass (part b)

Dependent

Acceleration of the trolley

Control

  • Total mass of the system (when varying force)
  • Resultant force (when varying mass)
  • The runway and its friction compensation

Results & processing

  • Acceleration against force is a straight line through the origin: acceleration is proportional to resultant force at constant mass.
  • Acceleration against mass is a curve (acceleration is inversely proportional to mass); a graph of acceleration against 1 / mass is a straight line. Both confirm F = m x a.

Where students lose marks

Not compensating for friction.

Fix: Tilt the runway until the trolley moves at constant velocity when tapped, so friction does not add a hidden systematic error.

Changing the total mass when investigating force.

Fix: Move masses from the trolley to the hanger rather than adding them, so the total mass being accelerated stays constant.

Inaccurate timing of the trolley.

Fix: Use light gates with a data logger (and a card of known length) rather than a hand-held stopwatch.

Improve the method

  • Friction-compensate the runway before taking readings.
  • Use light gates and a data logger for accurate acceleration measurements.
  • Transfer masses (do not add them) when varying the force, and repeat each reading.

Try it — exam-style

Medium
ORIGINAL

A resultant force of 6.0 N acts on a trolley of mass 1.5 kg. Calculate its acceleration.

[2 marks]

Total for this question: 2

Medium
ORIGINAL

When investigating how force affects acceleration, explain why masses are moved from the trolley onto the hanger rather than simply added to the hanger.

[2 marks]

Total for this question: 2

Questions are written in the style of past AQA papers — never copied from them.

Drill it properly

SUVAT trainer

Drill the motion equations that sit alongside F = m x a.

Physics equations

F = m x a and the forces and motion equations you need.

Stuck on acceleration, force and mass?

This practical is really a Newton's second law question with a fair-test twist — I drill the variable control and the F = m x a maths. Free intro call, then a free first lesson.

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