Overview
What you’ll learn
- Sort quantities into scalars and vectors without hesitation.
- Calculate weight with W = m g and locate the centre of mass.
- Find resultant forces and read free-body diagrams.
- Extract speed, acceleration and distance from motion graphs.
- Use a = Δv ÷ t and F = m a fluently, and v² − u² = 2 a s (Higher).
- State Newton’s laws, give third-law pairs, and describe the acceleration practical.
Specification checklist (AQA 8463 · Edexcel 1PH0 · OCR Gateway J249)
Statements are paraphrased from the shared DfE subject content and grouped by tier. Foundation content is studied by every student; Higher statements are examined on Higher-tier papers only, and statements badged Physics only are examined in separate (triple) Physics, not Combined Science. QuizQuip is not affiliated with AQA, Pearson Edexcel or OCR.
Foundation — every student
- 8.1Distinguish scalars (magnitude only — distance, speed, time, mass, energy) from vectors (magnitude and direction — displacement, velocity, acceleration, force, weight, momentum).
- 8.2Describe contact forces (friction, air resistance, tension, normal contact) and non-contact forces (gravitational, electrostatic, magnetic) as vector quantities with a size and direction.
- 8.3Explain weight as the force acting on an object through gravity, calculate it using weight = mass × gravitational field strength (W = m g), and describe weight as measured in newtons with a calibrated spring balance (newtonmeter).
- 8.4Describe that the weight of an object acts from its centre of mass and that g differs slightly across the Earth but is treated as 9.8 N/kg (or 10 N/kg) in calculations.
- 8.5Draw and interpret free-body diagrams, calculate resultant forces as vectors acting along a line, and explain how a zero resultant keeps an object at rest or at constant velocity.
- 8.6Draw and interpret distance–time graphs: gradient = speed, and use velocity–time graphs where gradient = acceleration and the area under the graph = distance.
- 8.8State Newton’s three laws: (1) an object stays at rest or at constant velocity unless acted on by a resultant force; (2) the resultant force on an object equals mass × acceleration (F = m a); (3) forces occur in equal and opposite pairs acting on different objects.
- 8.10Describe the required practical: investigating how force and mass affect the acceleration of a trolley, using light gates or ticker tape, with method, variables and graph.
- 8.11Describe examples of Newton’s third law pairs and explain that the two forces act on different objects.
Higher — Higher tier only
- 8.7Calculate acceleration using a = Δv ÷ t and, for uniform acceleration, use v² − u² = 2 a s. (The second equation is Higher tier.)
- 8.9Explain inertia (the tendency to keep moving or stay still) and define inertial mass as the ratio of force over acceleration. (Higher)
Key points
- 1Scalars have magnitude only (distance, speed, mass, time); vectors have magnitude and direction (force, velocity, acceleration).
- 2Weight W = m g: measured in newtons with a newtonmeter; acts from the centre of mass; g ≈ 9.8 N/kg.
- 3Resultant force: a single force with the same effect as all the forces combined — zero resultant = constant velocity (or rest).
- 4d–t graph: gradient = speed · v–t graph: gradient = acceleration, area = distance.
- 5a = Δv ÷ t; for uniform acceleration v² − u² = 2 a s (Higher).
- 6Newton 1: no resultant force → no change in velocity · Newton 2: F = m a · Newton 3: equal and opposite pairs on different objects.
- 7Inertia (Higher): the tendency to resist changes in motion; inertial mass = F ÷ a.
- 8Required practical: trolley, light gates — vary force (keep mass constant) or vary mass (keep force constant); a ∝ F and a ∝ 1/m.
Notes · 1 of 5
Scalars, vectors and weight
Direction is the difference between 60 km/h and 60 km/h north.
| Scalars (magnitude only) | Vectors (magnitude + direction) |
|---|---|
| Distance | Displacement |
| Speed | Velocity |
| Mass | Weight, force |
| Time, energy, temperature | Acceleration, momentum |
A vector is drawn as an arrow: length for size, direction for direction. Weight is the vector force of gravity on an object: W = m g, in newtons, acting from the centre of mass straight towards Earth. Your mass (kg) never changes wherever you are — your weight does: on the Moon (g ≈ 1.6 N/kg) you would weigh about a sixth of your Earth weight while keeping the same mass.
Notes · 2 of 5
Resultant forces and free-body diagrams
Add the arrows; the single arrow that replaces them is the resultant.
A free-body diagram draws every force on one object as an arrow. Along a straight line, forces in opposite directions subtract: a car with 800 N of engine thrust and 300 N of drag has a resultant of 800 − 300 = 500 N forward — so it accelerates. When forces balance (resultant = zero), Newton’s first law applies: the object stays at rest or moves at constant velocity. A parachutist at terminal velocity is not force-free — drag exactly cancels weight.
Notes · 3 of 5
Motion graphs
Gradient tells the story; on a v–t graph the area does too.
| Feature | Distance–time graph | Velocity–time graph |
|---|---|---|
| Gradient | Speed | Acceleration |
| Horizontal line | Stationary | Constant velocity |
| Straight slope | Constant speed | Constant acceleration |
| Curve | Changing speed | Changing acceleration |
| Area under graph | — | Distance travelled |
Notes · 4 of 5
Newton's three laws
One law of stubbornness, one law of acceleration, one law of pairs.
- First law: an object stays at rest, or at constant velocity, unless a resultant force acts. No resultant means no change — not necessarily no motion.
- Second law: the resultant force is F = m a. Twice the force, twice the acceleration; twice the mass, half the acceleration.
- Third law: forces come in pairs — equal size, opposite direction, acting on different objects. A tyre pushes the road backwards; the road pushes the tyre forwards. Only the force on the tyre accelerates the car.
Inertia (Higher) is the name for the reluctance to change velocity that Newton’s first law describes. Inertial mass measures it: m = F ÷ a — how hard you must push for a given acceleration. A loaded lorry has more inertia than a bicycle, which is why the same braking force changes its velocity far more slowly.
Notes · 5 of 5
Required practical: force, mass and acceleration
A trolley, a light gate or two, and the cleanest F = m a evidence in physics.
- 1Set-up
A trolley on a tilted runway (tilt compensates friction); one light gate at the start and one at the end of a measured run; a card of known length on the trolley; a hanging weight on a string over a pulley provides the force.
- 2Vary the force
Keep the trolley (plus carried masses) the same. Add hanging masses to change the force — but move each added mass onto the trolley when unused, so the total mass being accelerated stays constant.
- 3Vary the mass
Keep the hanging weight (force) constant and load the trolley with extra masses to increase the mass.
- 4Record
Each light gate times the card, giving velocity before and after; the software computes acceleration. Repeat each run and average.
- 5Conclude
Graph a against F: a straight line through the origin (a ∝ F). Graph a against 1/m: also a straight line through the origin (a ∝ 1/m). Together these verify F = m a.
Variables: independent — the force (or the mass); dependent — the acceleration; controls — total mass (in the force experiment), runway tilt, friction, air temperature. Risks: falling masses — keep feet clear; the runway must be stable. Errors: light-gate card length measured inaccurately shifts every velocity; averaging repeats smooths timing noise.
Revise
Key terms
The words examiners expect you to use precisely.
- Scalar
- A quantity with magnitude only, such as mass, distance or speed.
- Vector
- A quantity with magnitude and direction, such as force, velocity or acceleration.
- Weight
- The force of gravity on an object, W = m g, acting from its centre of mass.
- Centre of mass
- The point where an object’s mass can be treated as concentrated; weight acts through it.
- Resultant force
- The single force with the same effect as all forces acting on an object combined.
- Free-body diagram
- A diagram showing every force on one object as an arrow.
Show 6 more key termsShow fewer key terms
- Acceleration
- The rate of change of velocity, a = Δv ÷ t, in m/s².
- Terminal velocity
- The constant velocity reached when drag balances weight (resultant zero).
- Inertia
- The tendency of an object to keep its current velocity; measured by inertial mass = F ÷ a (Higher).
- Newton’s third law pair
- Two equal, opposite forces acting on different objects.
- Light gate
- A sensor that times a card passing through, used to measure velocities in the acceleration practical.
- Newtonmeter
- A calibrated spring balance that reads weight (or any force) in newtons.
Revise
Common mistakes
Where students most often lose marks in this chapter — and what to do instead.
Mistake: Calling speed a vector.
Speed ignores direction; velocity is the vector.
Instead: Speed is a scalar; velocity = speed with a direction.
Mistake: Saying weight and mass are the same thing.
Mass is kilograms of stuff; weight is the gravity force in newtons.
Instead: W = m g: mass stays constant everywhere; weight changes with g.
Show 10 more mistakesShow fewer mistakes
Mistake: Saying a moving object needs a resultant force to keep moving.
Newton’s first law says the opposite.
Instead: No resultant force means constant velocity — forces are needed to *change* velocity, not to sustain it.
Mistake: Drawing acceleration and velocity arrows the same way without thinking.
Acceleration is the change in velocity — it can be opposite to the motion.
Instead: Deceleration is acceleration opposite to the velocity direction.
Mistake: Reading the area under a distance–time graph.
Area has no meaning on a d–t graph.
Instead: Area = distance only on a velocity–time graph; gradient = speed on d–t.
Mistake: Forgetting to subtract friction when using F = m a.
F must be the resultant force.
Instead: Resultant = driving force − resistive forces, then F = m a.
Mistake: Describing a third-law pair as weight and normal contact force.
Those two act on the same object — they are an equilibrium, not a third-law pair.
Instead: Third-law pairs act on different objects: Earth pulls you (weight); you pull Earth upwards.
Mistake: Doubling mass and expecting double the acceleration for the same force.
Mass resists acceleration.
Instead: a = F ÷ m: doubling mass halves the acceleration.
Mistake: Saying terminal velocity means no forces act.
Weight and drag still act — they just balance.
Instead: Terminal velocity = zero resultant force, with weight = drag.
Mistake: Using v² − u² = 2 a s when acceleration is not uniform.
The equation only works for constant acceleration.
Instead: For changing acceleration, use the v–t graph area and tangents.
Mistake: In the practical, adding hanging masses without moving them onto the trolley.
The accelerating mass quietly changes, confounding the experiment.
Instead: Keep the total accelerated mass constant by carrying spare masses on the trolley.
Mistake: Quoting weight in kilograms.
Weight is a force — newtons.
Instead: Mass in kg; weight in N (W = m g).
Check yourself
Quick quiz
24 questions with instant explanations. About 5 minutes.
Question 1 of 3
- Question 1: current question
- Question 2: not answered
- Question 3: not answered
Sort scalars and vectors
To describe a force completely you must state its size and
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Practise
Topical questions
12 exam-style questions with model answers and mark schemes.
A set of structured and calculation questions matched to this chapter, in three tiers, each with a model answer, mark scheme and examiner tip. Higher-tier and Physics-only questions are tagged.
Practise topical questionsExam practice
Practice paper
A 30-mark paper in the style of a GCSE paper, with a separate mark scheme. Give yourself 40 min.
Question paper
Chapter 8 Practice Paper
30 marks · 40 min · 5 pages
10 multiple-choice questions and structured questions with answer lines. Chapter 8: scalars and vectors, weight, resultant forces and free-body diagrams, motion graphs, a = Δv ÷ t, v² − u² = 2as (Higher), Newton’s laws, inertia and the acceleration practical.
Mark scheme
PROChapter 8 Practice Paper — mark scheme
Answers · Marking points · 3 pages
Model answers with a mark for each creditworthy point — for marking at home or in class.
How is this chapter examined?
Paper 1
1 h 45 · 100 marks
Chapters 1–7: energy, electricity, particle model, atomic structure
Paper 2
1 h 45 · 100 marks
Chapters 8–18: forces, waves, magnetism and electromagnetism, space physics
Tiers
Foundation (grades 1–5) · Higher (grades 4–9)
Higher assumes all Foundation content; the equation sheet is printed
Want a full paper? Try the Paper 1-style (Foundation), Paper 1-style (Higher), Paper 2-style (Foundation), Paper 2-style (Higher), Required practicals practice sets.
Questions
Frequently asked questions
How do I remember scalars vs vectors?
Ask “would direction change the answer?” If yes, it is a vector. Speed 60 km/h is a scalar; 60 km/h north is a velocity. Force, weight, acceleration and momentum are always vectors.
Why do I keep seeing “resultant” in every mark scheme?
Because only the resultant force matters for motion. Subtract opposing forces first, then apply F = m a to the resultant — using the raw engine force alone is the classic lost mark.
When do I use v² − u² = 2as?
(Higher) When acceleration is uniform and time is missing. If a question gives distances but no times — or asks for distance without time — this is the equation that skips time entirely.
What makes two forces a Newton’s-third-law pair?
Equal size, opposite direction, different objects, same type of force. Weight and the table’s normal force fail the test: they act on the same object.
Is this chapter examined on both papers?
Forces sit in AQA Paper 2 and the middle of the Edexcel and OCR courses. v² − u² = 2as and inertial mass are Higher-only; everything else appears on both tiers.
Does QuizQuip have any connection to the exam boards?
No. AQA, Pearson Edexcel and OCR are named only to identify the specifications this content supports. QuizQuip is not affiliated with, endorsed by, or connected to AQA, Pearson Edexcel or OCR, and no past-paper or specimen material is reproduced.
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Chapter 9: Stopping distances