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3.4 Mechanics and materials

10 dot points across 10 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do solid materials respond when we stretch or compress them?

Density, Hooke's law and the spring constant, elastic and plastic behaviour, tensile stress and strain, the energy stored in a stretched material, and the difference between brittle and ductile behaviour.
A focused answer to AQA A-Level Physics 3.4.2.1, covering density, Hooke's law and the spring constant, elastic and plastic behaviour, tensile stress and strain, the elastic strain energy stored in a stretched material, and brittle versus ductile behaviour.
10 min answer →

Why can energy change form but never be created or destroyed?

The principle of conservation of energy, interconversion of kinetic and gravitational potential energy, energy dissipated by resistive forces, and applying conservation of energy to falling and oscillating systems.
A focused answer to AQA A-Level Physics 3.4.1.8, covering the principle of conservation of energy, the interconversion of kinetic and gravitational potential energy, energy dissipated by resistive forces, and applying conservation of energy to falling and oscillating systems.
9 min answer →

What makes an object turn, and when does it stay balanced?

The moment of a force about a point, the principle of moments, couples and torque, the centre of mass, and the conditions for the equilibrium of a rigid body under coplanar forces.
A focused answer to AQA A-Level Physics 3.4.1.2, covering the moment of a force, the principle of moments, couples and torque, the position of the centre of mass, and the conditions a rigid body must satisfy to remain in equilibrium.
9 min answer →

What stays constant when objects collide or explode apart?

Momentum as mass times velocity, the principle of conservation of momentum, force as rate of change of momentum, impulse and the area under a force-time graph, and elastic and inelastic collisions.
A focused answer to AQA A-Level Physics 3.4.1.6, covering momentum as mass times velocity, the principle of conservation of momentum, force as the rate of change of momentum, impulse and the area under a force-time graph, and the difference between elastic and inelastic collisions.
10 min answer →

How do displacement, velocity and acceleration relate when motion is in a straight line?

Definitions of displacement, speed, velocity and acceleration, interpreting motion graphs, the equations of uniformly accelerated motion (suvat), and motion under gravity.
A focused answer to AQA A-Level Physics 3.4.1.3, covering displacement, speed, velocity and acceleration, the interpretation of displacement-time and velocity-time graphs, the suvat equations of uniformly accelerated motion, and motion under gravity.
10 min answer →

How do forces determine the way objects move?

Newton's three laws of motion, the equation F = ma for constant mass, the meaning of inertia and inertial mass, and applying the laws to connected bodies and everyday situations.
A focused answer to AQA A-Level Physics 3.4.1.5, covering Newton's three laws of motion, the equation F = ma for an object of constant mass, the meaning of inertia and inertial mass, and how the laws are applied to connected and everyday systems.
9 min answer →

Why does a projectile follow a curved path, and how do we predict where it lands?

Independence of horizontal and vertical motion, applying the suvat equations to projectiles launched horizontally and at an angle, and the effect of air resistance on the trajectory.
A focused answer to AQA A-Level Physics 3.4.1.4, covering the independence of horizontal and vertical motion, applying the suvat equations to projectiles launched horizontally and at an angle, and the effect of air resistance on the trajectory.
10 min answer →

How do we add and resolve quantities that have direction as well as size?

Distinguishing scalars and vectors, adding vectors by calculation and scale drawing, resolving a vector into perpendicular components, and the conditions for equilibrium of coplanar forces.
A focused answer to AQA A-Level Physics 3.4.1.1, covering the difference between scalars and vectors, adding vectors by calculation and scale drawing, resolving vectors into perpendicular components, and the conditions for the equilibrium of coplanar forces.
9 min answer →

How do we measure the stiffness of a material independently of its shape?

The Young modulus as the ratio of tensile stress to tensile strain, the gradient of a stress-strain graph, the experiment to measure it for a wire, and interpreting stress-strain curves up to the breaking point.
A focused answer to AQA A-Level Physics 3.4.2.2, covering the Young modulus as the ratio of tensile stress to tensile strain, the gradient of a stress-strain graph, the experiment to measure it for a metal wire, and how to interpret stress-strain curves up to breaking.
9 min answer →

How do we measure energy transferred by a force and the rate of that transfer?

Work done by a force including a force at an angle, the relationship between power, work and velocity, kinetic and gravitational potential energy, and efficiency as the ratio of useful output to total input.
A focused answer to AQA A-Level Physics 3.4.1.7 and 3.4.1.8, covering work done by a force including forces at an angle, the relationship between power, work and velocity, kinetic and gravitational potential energy, and the definition of efficiency.
9 min answer →