GCSE Physics resources

AQA GCSE Forces

Newton’s Laws, Resultant Force and Acceleration

Newton’s laws describe how forces change motion. Use F = ma for the resultant force, not one individual force, and explain that acceleration is in the direction of the resultant.

AQA 8463AQA 8464 GCSE PhysicsCombined Science: Trilogy FoundationHigher

Start here

The revision snapshot

Newton’s laws describe how forces change motion. Use F = ma for the resultant force, not one individual force, and explain that acceleration is in the direction of the resultant.

By the end, you should be able to:

  • Connect force to acceleration.
  • Apply the forces model, evidence or method to an unfamiliar exam context.
  • Recognise and correct this wrong turn: Using the driving force instead of resultant.

Before you revise

Diagnostic question

Choose an answer from memory. Your result tells you what to watch for in the guide.

Which statement correctly summarises Newton’s laws, resultant force and acceleration?

Core revision guide

Learn the model, then use it

Newton’s Laws, Resultant Force and Acceleration questions become manageable when the central model, evidence and exam method are kept together. Read the explanation, test the misconception and then apply the idea without looking back.

Connect force to acceleration

Newton’s laws describe how forces change motion. Use F = ma for the resultant force, not one individual force, and explain that acceleration is in the direction of the resultant.

Build the physics picture

The resultant force is the vector sum of all forces. If it is zero, velocity is constant; if it is not zero, acceleration is in the resultant-force direction. For constant mass, F = ma links the size of the acceleration to the resultant, not to a single driving force.

The relationship for this guide

Newton’s second law: F = ma (N, kg, m/s²). Choose each relationship from the physical change described, convert quantities into compatible units and keep the unit beside the final answer.

A 10 kilogram trolley has 60 newtons right and 20 newtons left, producing 40 newtons and 4.0 metres per second squared right.
Combine forces with direction first, then use F = ma with the resultant force.Open the full-size exam diagram
Newton’s second lawF = maN, kg, m/s²

Misconception clinic

Replace the tempting answer

Read each belief, say what is wrong with it, then compare your correction.

Tempting idea: Using the driving force instead of resultant.

Use instead: Newton’s laws describe how forces change motion. Use F = ma for the resultant force, not one individual force, and explain that acceleration is in the direction of the resultant.

Tempting idea: Putting third-law pairs on one object.

Use instead: The resultant force is the vector sum of all forces. If it is zero, velocity is constant; if it is not zero, acceleration is in the resultant-force direction. For constant mass, F = ma links the size of the acceleration to the resultant, not to a single driving force.

Tempting idea: Saying force is needed to keep constant speed.

Use instead: Draw the force diagram, calculate the resultant, apply F = ma and state the direction of acceleration.

Retrieval practice

Quick checks

1. Which exam method is most reliable for Newton’s laws, resultant force and acceleration?

2. Which statement correctly applies Newton’s laws, resultant force and acceleration to a question?

3. A pupil writes: “Using the driving force instead of resultant.” Which replacement is accurate?

Explore the relationship

Newton law model

Change the resultant force or mass, then calculate acceleration using F = ma.

What to notice: use the readout to describe how one variable changes when the other is controlled.

Worked examples

See the method being built

These examples expose the difference between a secure connect force to acceleration method and the common error “Using the driving force instead of resultant.”.

Example 1 · Find acceleration

A 3.0 kg trolley has resultant force 12 N right. Calculate acceleration.

  1. Use F = ma.
  2. Rearrange a = F/m.
  3. State direction.
Show the answer

a = 12 ÷ 3.0 = 4.0 m/s² to the right.

Example 2 · Find resultant

A car has 800 N driving force and 300 N resistance. Find resultant force.

  1. Forces are opposite.
  2. Subtract 300 from 800.
  3. State direction of larger force.
Show the answer

Resultant = 500 N forwards.

Example 3 · Newton’s third law

A swimmer pushes water backwards. State the paired force.

  1. Name the second object.
  2. Reverse direction.
  3. Keep equal magnitude.
Show the answer

The water pushes the swimmer forwards with an equal and opposite force.

Exam precision

Exam technique: Connect force to acceleration

Do this: Draw the force diagram, calculate the resultant, apply F = ma and state the direction of acceleration.

Independent practice

Exam-style questions

Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.

1. State Newton’s first law for a zero resultant force.

[1 mark]
Show marking guidance and model answer

Marking guidance: Award one mark for the precise statement shown in the model answer.

Model answer: An object remains at rest or continues at constant velocity.

2. Calculate force on a 4.0 kg object accelerating at 2.5 m/s².

[3 marks]
Show marking guidance and model answer

Marking guidance: Award one mark for the correct relationship, one for a valid substitution and one for the final answer with its unit.

Model answer: F = ma = 4.0 × 2.5 = 10 N.

3. Explain why a heavier trolley accelerates less for the same resultant force.

[3 marks]
Show marking guidance and model answer

Marking guidance: Award up to 3 marks for distinct physics points joined into a clear cause-and-effect chain.

Model answer: From a = F/m, greater mass gives smaller acceleration.

4. State what forces in a Newton-third-law pair act on.

[1 mark]
Show marking guidance and model answer

Marking guidance: Award one mark for the precise statement shown in the model answer.

Model answer: Different objects.

5. A 10 N force right and 14 N force left act on an object. State acceleration direction.

[2 marks]
Show marking guidance and model answer

Marking guidance: 2 marks are available for relevant, linked physics points that match the model answer.

Model answer: Left, because the resultant is 4 N left.

6. Explain why balanced forces do not mean an object must be stationary.

[3 marks]
Show marking guidance and model answer

Marking guidance: Award up to 3 marks for distinct physics points joined into a clear cause-and-effect chain.

Model answer: It can move at constant velocity when resultant force is zero.

Questions pupils ask

Newton’s Laws, Resultant Force and Acceleration FAQs

What is the main idea in Newton’s Laws, Resultant Force and Acceleration?

Newton’s laws describe how forces change motion. Use F = ma for the resultant force, not one individual force, and explain that acceleration is in the direction of the resultant.

What mistake should I avoid in Newton’s Laws, Resultant Force and Acceleration?

Using the driving force instead of resultant. The resultant force is the vector sum of all forces. If it is zero, velocity is constant; if it is not zero, acceleration is in the resultant-force direction. For constant mass, F = ma links the size of the acceleration to the resultant, not to a single driving force.

Useful next steps

Connect this guide to your next task

Motion Graphs, Speed and AccelerationUse graph gradient and area carefully. A curved distance–time graph shows changing speed; a horizontal velocity–time line shows constant velocity; a negative velocity can still have a positive speed.Forces, Elasticity and SpringsFor a spring obeying Hooke’s law, extension is proportional to force. The limit of proportionality is where the graph stops being straight; beyond the elastic limit the spring may not return to its original length.How to Answer GCSE Physics Calculation QuestionsA reliable calculation answer is a short chain of decisions. Make the physics visible so a marker can award method marks even if arithmetic slips. More free PhysicsUK resourcesBrowse revision, practical and exam-support resources. Try AQA GCSE Physics in PhysicsUK Exam StudioApply your knowledge to marked exam-style work.