What does AQA A-Level Physics module 3.4 Mechanics and materials cover?

It runs from scalars and vectors and moments, through kinematics (suvat and motion graphs), projectile motion, Newton's laws, momentum and impulse, work, energy and power, and conservation of energy, into the materials section: density, Hooke's law, stress, strain, elastic strain energy and the Young modulus. It is mostly an AS-level module that is reinforced and extended in the full A-Level.

Which equations recur most across module 3.4?

The suvat equations of uniformly accelerated motion, $F = ma$, $p = mv$ with conservation of momentum and impulse $F\Delta t = \Delta(mv)$, work $W = Fs\cos\theta$, power $P = Fv$, kinetic energy $\frac{1}{2}mv^2$, gravitational potential energy $mg\Delta h$, Hooke's law $F = kx$, stress $\sigma = \frac{F}{A}$, strain and the Young modulus $E = \frac{FL}{A\Delta L}$. Resolving vectors underpins almost all of them.

What is the single most common mistake in this module?

Swapping sine and cosine when resolving vectors, and treating momentum as a scalar. Remember the component adjacent to the angle uses cosine and the opposite component uses sine, and that momentum always carries a direction. In materials, the classic slip is using the diameter as the area instead of computing $A = \pi r^2$ from the radius.

How is the difference between elastic and inelastic collisions examined?

Momentum is conserved in every collision, but kinetic energy is conserved only in an elastic collision. A standard question gives a collision, asks you to use conservation of momentum to find a velocity, then compare kinetic energy before and after to classify it. If the objects stick together it is perfectly inelastic.

How should I revise the materials part of the module?

Learn the chain density, Hooke's law, stress and strain, then the Young modulus, and practise the wire experiment as a required practical. Be fluent in reading force-extension and stress-strain graphs: the area under force-extension is the elastic strain energy, and the gradient of the straight part of a stress-strain graph is the Young modulus.

EnglandPhysics

AQA A-Level Physics 3.4 Mechanics and materials: a complete overview of vectors, motion, forces, energy and material properties

A deep-dive AQA A-Level Physics guide to module 3.4 Mechanics and materials. Covers scalars and vectors, moments, kinematics and suvat, projectiles, Newton's laws, momentum, work, energy and power, conservation of energy, the bulk properties of solids and the Young modulus, with the calculations and exam patterns AQA repeats.

Generated by Claude Opus 4.822 min read3.4Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What module 3.4 actually demands
Vectors, moments and equilibrium
Kinematics and projectiles
Forces, momentum and energy
Materials
How module 3.4 is examined
Check your knowledge

What module 3.4 actually demands

Mechanics and materials is the problem-solving core of AQA A-Level Physics. Module 3.4 starts with the language of directed quantities (vectors), builds up the description of motion, then explains what causes motion (forces, momentum and energy), and finishes with how solid materials respond to forces. The examiners test two linked skills: clean definitions and laws, and the confident application of equations to multi-step numerical problems.

This guide walks through all the topics in specification order, then sets out the exam patterns AQA repeats. Each topic has a matching dot-point page with practice questions; this overview ties them together.

Vectors, moments and equilibrium

The module opens with scalars and vectors: which quantities have direction, how to add vectors tip to tail, how to find a resultant with Pythagoras and trigonometry, and how to resolve a vector into perpendicular components $F\cos\theta$ and $F\sin\theta$ . This single skill underpins slopes, projectiles and forces.

Moments extend this to turning: the moment of a force is $F \times d$ using the perpendicular distance, the principle of moments balances clockwise and anticlockwise turning, and a couple produces a torque with no resultant force. A rigid body is in equilibrium only when both the resultant force and the resultant moment are zero.

Kinematics and projectiles

Motion along a straight line introduces displacement, velocity and acceleration, motion graphs, and the suvat equations of uniformly accelerated motion, including motion under gravity. Projectile motion then treats horizontal and vertical motion as independent, linked only by a common time, with air resistance reducing range and height.

Forces, momentum and energy

Newton's laws give $F = ma$ for constant mass, the meaning of inertia, and the action-reaction pairs of the third law. Momentum is $p = mv$ , conserved in all collisions and explosions; the full second law is force as the rate of change of momentum, and impulse is the area under a force-time graph.

Work, energy and power defines work as $W = Fs\cos\theta$ , power as $P = Fv$ , kinetic energy as $\frac{1}{2}mv^2$ and gravitational potential energy as $mg\Delta h$ , with efficiency as useful output over total input. Conservation of energy ties these together: energy changes form but is never created or destroyed, with resistive forces dissipating mechanical energy as heat.

Materials

The materials section covers density, Hooke's law ( $F = kx$ ), elastic versus plastic behaviour, tensile stress and strain, the elastic strain energy (the area under a force-extension graph), and the Young modulus as the gradient of the straight part of a stress-strain graph. The Young-modulus wire experiment is a key required practical, and brittle versus ductile behaviour is read from stress-strain curves.

How module 3.4 is examined

A typical AQA profile for Mechanics and materials:

Multiple choice and short answer. Classifying scalars and vectors, stating Newton's laws, identifying elastic versus inelastic collisions, and recalling definitions of stress, strain and the Young modulus.
Calculations. Resolving forces, suvat problems, projectile ranges and times, $F = ma$ and connected bodies, conservation of momentum, work and power, and the Young modulus from wire data.
Graph and data questions. Reading motion graphs, force-time graphs (impulse), force-extension graphs (strain energy) and stress-strain graphs (Young modulus, elastic limit and breaking point).
Extended answers. Explaining the shape of a projectile path with air resistance, why airbags reduce force, and how a long, thin wire reduces uncertainty in the Young-modulus experiment.

Check your knowledge

A mix of recall and calculation questions covering module 3.4. Attempt them under timed conditions, then check against the solutions.

A 20 N force acts at 60 degrees above the horizontal. Find its horizontal and vertical components. (2 marks)
State the principle of moments. (2 marks)
A car accelerates from rest at $3.0 \text{ m s}^{-2}$ for 5.0 s. Find its final velocity and the distance travelled. (3 marks)
A ball is thrown horizontally at 8.0 m/s from a 5.0 m high table. Find the time to land. Take g as 9.8 m/s squared. (2 marks)
A resultant force of 18 N acts on a 3.0 kg mass. Find the acceleration. (1 mark)
A 0.40 kg ball moving at 5.0 m/s strikes a wall and rebounds at 3.0 m/s. Find the change in momentum. (2 marks)
A 2.0 kg object is lifted 3.0 m. Find the gain in gravitational potential energy. Take g as 9.8 m/s squared. (2 marks)
A wire of cross-sectional area $1.0 \times 10^{-6} \text{ m}^2$ and length 2.0 m extends 1.0 mm under a force of 40 N. Find the Young modulus. (3 marks)

Solutions

Eight questions covering module 3.4 from vector resolution through to the Young modulus. Work through each in turn.

Step 1: Q1 - Resolve a force into components

A force at an angle is resolved using trigonometry: the component adjacent to the angle uses cosine and the component opposite the angle uses sine. Always draw the triangle first to avoid swapping the two.

F_x = 20\cos 60^\circ = 20 \times 0.5 = 10 \text{ N}

F_y = 20\sin 60^\circ = 20 \times \frac{\sqrt{3}}{2} \approx 17.3 \text{ N}

Final answer: horizontal $10$ N, vertical $17.3$ N.

Step 2: Q2 - State the principle of moments

The principle of moments is the rotational equivalent of Newton's first law. For a rigid body to be in equilibrium, there must be no tendency to rotate about any point.

For a body in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about that point.

Step 3: Q3 - Kinematics: final velocity and distance

The car starts from rest ( $u = 0$ ) and accelerates uniformly, so both suvat equations can be applied directly. The velocity equation gives the speed, and the distance equation gives how far it has travelled.

v = u + at = 0 + 3.0 \times 5.0 = 15 \text{ m s}^{-1}

s = \frac{1}{2}at^2 = \frac{1}{2} \times 3.0 \times (5.0)^2 = 37.5 \text{ m}

Final answer: $v = 15 \text{ m s}^{-1}$ , distance $= 37.5$ m.

Step 4: Q4 - Projectile: time to land

The horizontal and vertical motions are independent. The ball has no initial vertical velocity (it is thrown horizontally), so the vertical motion is equivalent to free fall from height $5.0$ m. Setting up the vertical suvat equation and solving for time gives the answer.

s = \frac{1}{2}gt^2 \implies 5.0 = \frac{1}{2}(9.8)t^2 \implies t^2 = \frac{10.0}{9.8} \implies t \approx 1.0 \text{ s}

Final answer: time to land $\approx 1.0$ s.

Step 5: Q5 - Acceleration from Newton's second law

Newton's second law $F = ma$ relates the resultant force on an object to the acceleration it produces. Dividing the resultant force by the mass isolates the acceleration.

a = \frac{F}{m} = \frac{18}{3.0} = 6.0 \text{ m s}^{-2}

Final answer: $a = 6.0 \text{ m s}^{-2}$ .

Step 6: Q6 - Change in momentum (impulse)

Momentum is a vector, so its direction matters. Taking the initial direction of travel as positive, the rebound velocity is $-3.0$ m/s. The change in momentum is the final momentum minus the initial momentum.

\Delta p = m(v - u) = 0.40\bigl((-3.0) - 5.0\bigr) = 0.40 \times (-8.0) = -3.2 \text{ kg m s}^{-1}

The magnitude of the change in momentum is $3.2$ kg m s $^{-1}$ .

Step 7: Q7 - Gain in gravitational potential energy

Gravitational potential energy depends on the weight of the object and the vertical height through which it is lifted. The gain equals the work done against gravity.

\Delta E_p = mg\Delta h = 2.0 \times 9.8 \times 3.0 = 58.8 \text{ J}

Final answer: $58.8$ J.

Step 8: Q8 - Young modulus from wire data

The Young modulus is the ratio of stress to strain. Calculate stress (force per unit area) and strain (extension divided by original length) separately, then divide.

\text{stress} = \frac{F}{A} = \frac{40}{1.0 \times 10^{-6}} = 4.0 \times 10^7 \text{ Pa}

\text{strain} = \frac{\Delta L}{L} = \frac{1.0 \times 10^{-3}}{2.0} = 5.0 \times 10^{-4}

E = \frac{\text{stress}}{\text{strain}} = \frac{4.0 \times 10^7}{5.0 \times 10^{-4}} = 8.0 \times 10^{10} \text{ Pa}

Final answer: $E = 8.0 \times 10^{10}$ Pa.

Sources & how we know this

AQA A-level Physics (7408) specification — AQA (2017)