What does OCR Module 3 Forces and motion cover?

It covers describing motion with displacement, velocity and acceleration and the suvat equations, projectile motion resolved into independent components, forces in action including types of force, density and pressure, moments, couples and equilibrium with terminal velocity, work, energy and power with conservation and efficiency, materials with Hooke's law, stress, strain, the Young modulus and strain energy, and Newton's three laws with momentum, impulse and collisions.

Which equations recur most across Forces and motion?

The suvat equations $v = u + at$, $s = ut + \frac{1}{2}at^2$ and $v^2 = u^2 + 2as$, Newton's second law $F = ma$ and its momentum form $F = \frac{\Delta p}{\Delta t}$, moments as force times perpendicular distance, work $W = Fs\cos\theta$ and power $P = Fv$, kinetic energy $\frac{1}{2}mv^2$ and potential energy $mgh$, momentum $p = mv$ with impulse $F\Delta t = \Delta p$, and the Young modulus $E = \frac{\sigma}{\varepsilon}$ with strain energy $\frac{1}{2}k(\Delta x)^2$.

What is the most common mistake in this module?

Applying gravity to the horizontal motion of a projectile. Horizontal velocity stays constant when air resistance is ignored, and the two directions are linked only by the shared time. Close behind are sign errors in momentum problems with rebounds, confusing the force constant with the Young modulus, and using a suvat equation when the acceleration is not constant.

How is momentum examined in OCR Physics A?

Conservation of momentum problems set the total momentum before equal to the total after, with careful signs in one dimension, and many then ask whether the collision is elastic by comparing total kinetic energy before and after. Impulse questions use $F\Delta t = \Delta p$ or the area under a force-time graph, often in a safety context such as crumple zones, airbags and sports impacts.

How should I revise Forces and motion?

Drill the suvat and projectile method until it is automatic, then practise free-body diagrams, resolving forces, moments and equilibrium. Learn the energy and momentum conservation routines and the elastic-versus-inelastic test. For materials, master stress, strain and the Young modulus from a stress-strain graph and strain energy as an area. This module underpins Modules 5 and 6, so build it solidly first.

EnglandPhysics

OCR A-Level Physics A Forces and motion: kinematics, forces, energy, materials and momentum

A deep-dive OCR A-Level Physics A guide to Module 3, Forces and motion. Covers kinematics and projectiles, forces in action with moments and equilibrium, work, energy and power, materials and the Young modulus, and Newton's laws with momentum and impulse, with the calculations OCR repeats.

Generated by Claude Opus 4.818 min readH556 Module 3Updated 2026-06-02

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What this module actually demands
Kinematics, projectiles and forces
Energy, materials and momentum
How this module is examined
Check your knowledge

What this module actually demands

Forces and motion is the foundation of OCR Physics A. It starts from describing motion, builds to the forces that cause it and the conditions for equilibrium, develops the great conservation ideas of energy and momentum, and covers how real materials deform under load. The examiners reward fluent calculation, clear free-body diagrams and precise definitions, and the methods here underpin almost everything in Modules 5 and 6.

This guide walks through the topics in order and sets out the exam patterns OCR repeats. Each topic has a matching dot-point page with practice; this overview ties them together.

Kinematics, projectiles and forces

Motion and kinematics defines displacement, velocity and acceleration, interprets motion graphs through gradient and area, applies the suvat equations for constant acceleration, and treats free fall as motion with acceleration $g$ . Projectile motion separates the constant horizontal velocity from the vertical free fall, using the shared time to link them, and accounts for air resistance.

Forces in action identifies the forces on a body with free-body diagrams, uses density and pressure, calculates moments and couples, applies the principle of moments and the conditions for equilibrium, and explains terminal velocity.

Energy, materials and momentum

Work, energy and power defines work as $W = Fs\cos\theta$ , applies conservation of energy, uses kinetic energy $\frac{1}{2}mv^2$ and potential energy $mgh$ , and relates power to force and velocity with $P = Fv$ , including efficiency. Materials and the Young modulus applies Hooke's law, defines stress, strain and the Young modulus, finds strain energy as an area, and contrasts ductile, brittle and polymeric behaviour. Newton's laws and momentum states the three laws, conserves momentum in collisions and explosions, uses impulse $F\Delta t = \Delta p$ , and distinguishes elastic from inelastic collisions.

How this module is examined

A typical OCR profile for Forces and motion:

Calculations. Suvat and projectile problems, resultant forces and acceleration, moments and equilibrium, work, power and efficiency, momentum and impulse, and Young modulus from wire data.
Graph questions. Reading motion graphs, force-extension and stress-strain graphs, and force-time graphs for impulse.
Explanation and definition. Newton's laws, conditions for equilibrium, elastic versus inelastic collisions, and stiffness versus strength.
Extended answers. Free-body analysis on slopes, terminal velocity arguments, and energy bookkeeping in multi-stage problems.

Check your knowledge

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

State the two conditions for an object to be in equilibrium. (2 marks)
A car accelerates from rest at $4.0\ \text{m s}^{-2}$ for $6.0\ \text{s}$ . Find its final speed and the distance travelled. (2 marks)
A $2.0\ \text{kg}$ trolley at $3.0\ \text{m s}^{-1}$ collides with and sticks to a stationary $1.0\ \text{kg}$ trolley. Find the common velocity. (2 marks)
Define impulse and state its unit. (2 marks)
A wire of cross-sectional area $2.0 \times 10^{-7}\ \text{m}^2$ carries a load of $30\ \text{N}$ . Find the stress. (1 mark)
State the difference between an elastic and an inelastic collision. (2 marks)

Solutions

Q1: The resultant force is zero and the resultant moment about any point is zero.
Q2: $v = u + at = 0 + 4.0 \times 6.0 = 24\ \text{m s}^{-1}$ ; $s = ut + \frac{1}{2}at^2 = \frac{1}{2}(4.0)(6.0)^2 = 72\ \text{m}$ .
Q3: $2.0 \times 3.0 = (2.0 + 1.0)v$ , so $v = \frac{6.0}{3.0} = 2.0\ \text{m s}^{-1}$ .
Q4: Impulse is the change in momentum, $F\Delta t = \Delta p$ , measured in N s (equivalent to $\text{kg m s}^{-1}$ ).
Q5: $\sigma = \frac{F}{A} = \frac{30}{2.0 \times 10^{-7}} = 1.5 \times 10^{8}\ \text{Pa}$ .
Q6: In an elastic collision total kinetic energy is conserved; in an inelastic collision some kinetic energy is transferred to other stores. Momentum is conserved in both.

Sources & how we know this

OCR AS and A Level Physics A (H156, H556) specification — OCR (2015)