ForcesAQA GCSE Physics (8463)

Forces and their Interactions

Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next. (2026)

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Master the topic

Worked examples7 Key formulae1 Definitions10 Common mistakes7

Step-by-step worked examples

01.Classify quantities
Foundation
Question
Identify each as scalar or vector: (a) mass, (b) weight, (c) velocity, (d) speed, (e) time, (f) acceleration.
Solution
1. 1
  Apply definitions.
  $\text{(a) mass — scalar; (b) weight — vector; (c) velocity — vector; (d) speed — scalar; (e) time — scalar; (f) acceleration — vector.}$
Answer
Scalars: mass, speed, time. Vectors: weight, velocity, acceleration.
02.Distance vs displacement
Foundation
Question
A pupil walks 50 m east, then 30 m west. Calculate (a) total distance walked and (b) displacement.
Solution
1. 1
  Distance = total path.
  $\text{Distance = 50 + 30 = 80 m}$
2. 2
  Displacement = net straight-line.
  $\text{Displacement = 50 east + 30 west = 20 m east}$
Answer
(a) 80 m; (b) 20 m east.
03.Classify forces
Foundation
Question
Classify each force as contact or non-contact: (a) air resistance on a sky-diver, (b) gravity on the Moon, (c) tension in a rope, (d) repulsion between two N poles.
Solution
1. 1
  Apply definitions.
  $\text{(a) contact (air molecules); (b) non-contact; (c) contact (rope touching object); (d) non-contact (magnetic).}$
Answer
(a) contact (b) non-contact (c) contact (d) non-contact.
04.Weight on Earth
Foundation
Question
Calculate the weight of a 12 kg suitcase on Earth (g = 9.8 N/kg).
Solution
1. 1
  Apply W = mg.
  $W = 12 \times 9.8 = 117.6\,\text{N}$
Answer
About 118 N.
05.Weight on the Moon
Higher
Question
An astronaut has mass 80 kg. Find her weight on (a) Earth (g = 9.8), (b) the Moon (g = 1.6).
Solution
1. 1
  Earth.
  $W_E = 80 \times 9.8 = 784\,\text{N}$
2. 2
  Moon.
  $W_M = 80 \times 1.6 = 128\,\text{N}$
Answer
Earth: 784 N. Moon: 128 N (about 16 % of her Earth weight).
06.Find resultant of parallel forces
Foundation
Question
Two horses pull a barge: one with 300 N north, the other with 200 N south. Find the resultant.
Solution
1. 1
  Subtract opposites.
  $F = 300 - 200 = 100\,\text{N north}$
Answer
100 N north.
07.Balanced book
Foundation
Question
A 0.5 kg book rests on a table. (a) Calculate its weight. (b) What is the normal reaction from the table? (c) What is the resultant force?
Solution
1. 1
  Weight.
  $W = mg = 0.5 \times 9.8 = 4.9\,\text{N}$
2. 2
  Normal reaction.
  $R = 4.9\,\text{N upward (balanced)}$
3. 3
  Resultant.
  $F_{\text{net}} = 4.9 - 4.9 = 0\,\text{N}$
Answer
Weight 4.9 N down; normal 4.9 N up; resultant 0 N.

Key formulae

Weight
$W = m g$
- $W$
  — Weight (N)
- $m$
  — Mass (kg)
- $g$
  — Gravitational field strength (N/kg)
When to use
To find weight from mass, or rearrange to find m or g. NOT on equation sheet — must recall.

Practice with flashcards

Card 1 of 100 known · 0 to review

Key definitions and keywords

ScalarExaminer keyword: A quantity that has magnitude only (no direction). Examples: mass, time, energy.
VectorExaminer keyword: A quantity that has both magnitude AND direction. Examples: force, velocity, displacement.
DisplacementExaminer keyword: Straight-line distance from start to finish in a specified direction (vector).
Contact forceExaminer keyword: A force that acts between objects in physical contact.
Non-contact forceExaminer keyword: A force that acts between objects not in contact (across space).
MassExaminer keyword: A measure of the amount of matter in an object. Scalar. SI unit kg.
WeightExaminer keyword: The gravitational force acting on an object's mass. Vector. SI unit N.
Gravitational field strength (g)Examiner keyword: The force per unit mass acting on an object in a gravitational field. Units: N/kg. On Earth ≈ 9.8 N/kg.
Resultant forceExaminer keyword: A single force that has the same effect as all the forces acting on an object combined.
Free-body diagramExaminer keyword: A diagram showing all the forces acting on a single chosen object, drawn as arrows.

Common mistakes and misconceptions

Mistake
Saying distance and displacement are the same.
Why it happens
Both sound similar.
How to avoid it
Distance is total path (scalar). Displacement is net change in position (vector).
Mistake
Calling force a scalar.
Why it happens
Force often given as just a number.
How to avoid it
Always state direction; force is a vector.
Mistake
Calling gravity a contact force because objects on Earth touch the ground.
Why it happens
Confusing the action of gravity with the normal reaction.
How to avoid it
Gravity acts BETWEEN the Earth's centre and the object — it doesn't require contact. The reaction with the ground is a separate, contact force (normal).
Mistake
Using 'mass' and 'weight' interchangeably.
Why it happens
Everyday English.
How to avoid it
Mass in kg = how much matter. Weight in N = gravitational force.
Mistake
Using g = 10 instead of 9.8.
Why it happens
Older textbooks.
How to avoid it
AQA 2026 uses g = 9.8 N/kg from the data sheet.
Mistake
Saying balanced forces mean no motion.
Why it happens
Confusing 'no acceleration' with 'no motion'.
How to avoid it
Balanced = constant velocity OR rest. An object can move steadily with zero resultant force.
Mistake
Missing forces from a free-body diagram.
Why it happens
Forgetting weight or normal reaction.
How to avoid it
Always check gravity (weight), normal, friction, drive, applied forces.

ForcesAQA GCSE Physics (8463)

Forces and their Interactions

Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next. (2026)

PreviousNext

Master the topic

Worked examples7 Key formulae1 Definitions10 Common mistakes7

Step-by-step worked examples

01.Classify quantities
Foundation
Question
Identify each as scalar or vector: (a) mass, (b) weight, (c) velocity, (d) speed, (e) time, (f) acceleration.
Solution
1. 1
  Apply definitions.
  $\text{(a) mass — scalar; (b) weight — vector; (c) velocity — vector; (d) speed — scalar; (e) time — scalar; (f) acceleration — vector.}$
Answer
Scalars: mass, speed, time. Vectors: weight, velocity, acceleration.
02.Distance vs displacement
Foundation
Question
A pupil walks 50 m east, then 30 m west. Calculate (a) total distance walked and (b) displacement.
Solution
1. 1
  Distance = total path.
  $\text{Distance = 50 + 30 = 80 m}$
2. 2
  Displacement = net straight-line.
  $\text{Displacement = 50 east + 30 west = 20 m east}$
Answer
(a) 80 m; (b) 20 m east.
03.Classify forces
Foundation
Question
Classify each force as contact or non-contact: (a) air resistance on a sky-diver, (b) gravity on the Moon, (c) tension in a rope, (d) repulsion between two N poles.
Solution
1. 1
  Apply definitions.
  $\text{(a) contact (air molecules); (b) non-contact; (c) contact (rope touching object); (d) non-contact (magnetic).}$
Answer
(a) contact (b) non-contact (c) contact (d) non-contact.
04.Weight on Earth
Foundation
Question
Calculate the weight of a 12 kg suitcase on Earth (g = 9.8 N/kg).
Solution
1. 1
  Apply W = mg.
  $W = 12 \times 9.8 = 117.6\,\text{N}$
Answer
About 118 N.
05.Weight on the Moon
Higher
Question
An astronaut has mass 80 kg. Find her weight on (a) Earth (g = 9.8), (b) the Moon (g = 1.6).
Solution
1. 1
  Earth.
  $W_E = 80 \times 9.8 = 784\,\text{N}$
2. 2
  Moon.
  $W_M = 80 \times 1.6 = 128\,\text{N}$
Answer
Earth: 784 N. Moon: 128 N (about 16 % of her Earth weight).
06.Find resultant of parallel forces
Foundation
Question
Two horses pull a barge: one with 300 N north, the other with 200 N south. Find the resultant.
Solution
1. 1
  Subtract opposites.
  $F = 300 - 200 = 100\,\text{N north}$
Answer
100 N north.
07.Balanced book
Foundation
Question
A 0.5 kg book rests on a table. (a) Calculate its weight. (b) What is the normal reaction from the table? (c) What is the resultant force?
Solution
1. 1
  Weight.
  $W = mg = 0.5 \times 9.8 = 4.9\,\text{N}$
2. 2
  Normal reaction.
  $R = 4.9\,\text{N upward (balanced)}$
3. 3
  Resultant.
  $F_{\text{net}} = 4.9 - 4.9 = 0\,\text{N}$
Answer
Weight 4.9 N down; normal 4.9 N up; resultant 0 N.

Key formulae

Weight
$W = m g$
- $W$
  — Weight (N)
- $m$
  — Mass (kg)
- $g$
  — Gravitational field strength (N/kg)
When to use
To find weight from mass, or rearrange to find m or g. NOT on equation sheet — must recall.

Practice with flashcards

Card 1 of 100 known · 0 to review

Key definitions and keywords

ScalarExaminer keyword: A quantity that has magnitude only (no direction). Examples: mass, time, energy.
VectorExaminer keyword: A quantity that has both magnitude AND direction. Examples: force, velocity, displacement.
DisplacementExaminer keyword: Straight-line distance from start to finish in a specified direction (vector).
Contact forceExaminer keyword: A force that acts between objects in physical contact.
Non-contact forceExaminer keyword: A force that acts between objects not in contact (across space).
MassExaminer keyword: A measure of the amount of matter in an object. Scalar. SI unit kg.
WeightExaminer keyword: The gravitational force acting on an object's mass. Vector. SI unit N.
Gravitational field strength (g)Examiner keyword: The force per unit mass acting on an object in a gravitational field. Units: N/kg. On Earth ≈ 9.8 N/kg.
Resultant forceExaminer keyword: A single force that has the same effect as all the forces acting on an object combined.
Free-body diagramExaminer keyword: A diagram showing all the forces acting on a single chosen object, drawn as arrows.

Common mistakes and misconceptions

Mistake
Saying distance and displacement are the same.
Why it happens
Both sound similar.
How to avoid it
Distance is total path (scalar). Displacement is net change in position (vector).
Mistake
Calling force a scalar.
Why it happens
Force often given as just a number.
How to avoid it
Always state direction; force is a vector.
Mistake
Calling gravity a contact force because objects on Earth touch the ground.
Why it happens
Confusing the action of gravity with the normal reaction.
How to avoid it
Gravity acts BETWEEN the Earth's centre and the object — it doesn't require contact. The reaction with the ground is a separate, contact force (normal).
Mistake
Using 'mass' and 'weight' interchangeably.
Why it happens
Everyday English.
How to avoid it
Mass in kg = how much matter. Weight in N = gravitational force.
Mistake
Using g = 10 instead of 9.8.
Why it happens
Older textbooks.
How to avoid it
AQA 2026 uses g = 9.8 N/kg from the data sheet.
Mistake
Saying balanced forces mean no motion.
Why it happens
Confusing 'no acceleration' with 'no motion'.
How to avoid it
Balanced = constant velocity OR rest. An object can move steadily with zero resultant force.
Mistake
Missing forces from a free-body diagram.
Why it happens
Forgetting weight or normal reaction.
How to avoid it
Always check gravity (weight), normal, friction, drive, applied forces.

Forces and their Interactions

Master the topic

Step-by-step worked examples

01.Classify quantities

02.Distance vs displacement

03.Classify forces

04.Weight on Earth

05.Weight on the Moon

06.Find resultant of parallel forces

07.Balanced book

Key formulae

Practice with flashcards

Key definitions and keywords

Common mistakes and misconceptions

Forces and their Interactions

Master the topic

Step-by-step worked examples

01.Classify quantities

02.Distance vs displacement

03.Classify forces

04.Weight on Earth

05.Weight on the Moon

06.Find resultant of parallel forces

07.Balanced book

Key formulae

Practice with flashcards

Key definitions and keywords

Common mistakes and misconceptions