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Module 3: Forces and Motion

The forces and motion module is all taught in year 12 and forms half of Modelling Physics.  The topic builds on your GCSE knowledge of forces and motion and it is essential that you have a good grasp of this before starting the A Level course. Visit the "Preparing for A Level" section for more information.


The forces and motion module is split in to 5 sub-modules: 

3.1 Motion

3.1 Motion and 2.0 Uncertainty analysis

Image by Davide Cantelli

By the end of this topic you should be able to:


  • Describe the difference between accuracy and precision and random and systematic error

  • Calculate and combine percentage and absolute uncertainties

  • Construct error bars and lines of worst fit to establish uncertainty in a gradient

  • Calculate percentage difference 

  • Define and calculate displacement, instantaneous speed, average speed, velocity and acceleration

  • Describe features of distance-time and displacement-time graphs and calculate the gradient to find velocity (including for non-linear graphs)

  • Describe features of speed-time and velocity-time graphs and calculate the gradient to find acceleration and area underneath to find total distance/displacement (including for non-linear graphs)

  • Use the equations of motion in calculations

  • Describe methods to measure acceleration of free-fall (g)

  • Define and explain factors that affect stopping distance, thinking distance and braking distance

  • Calculate variables in projectile motion by splitting into horizontal and vertical components of motion

3.2 Forces
Image by Artur Tumasjan

3.2 Forces & 3.5 Newton's Laws and momentum

By the end of this topic you should be able to:​

  • Describe how force, mass and acceleration are linked

  • Describe the difference between weight and mass, and describe how to find the centre of mass

  • State different types of force and describe how these act on objects

  • Describe how drag forces act in fluids so objects reach terminal velocity including an experiment to demonstrate this

  • Define what is meant by density and pressure and use this to describe pressure in fluids and Archimedes’ principle

  • Construct free body diagrams

  • Resolve forces to find a resultant force and resolve forces into components

  • Define the principle of moments and calculate moments

  • Define torque and calculate this for objects

  • State and explain Newton’s three laws of motion​

  • Calculate momentum

  • Define the principle of conservation of momentum and use this to calculate change in momentum during collisions and explosions

  • Define what is meant by impulse and link this to force-time graphs

  • Describe what is meant by elastic and inelastic collisions

  • Solve problems involving change in momentum in two dimensions

3.3 Work, energy and power

3.3 Work, energy and power

Image by Tim Foster

By the end of this topic you should be able to:​

  • Describe different types and transfers of energy

  • Calculate and define work done, including for forces at angles

  • Derive the equation for kinetic energy and use this in calculations

  • Derive the equation for gravitational potential energy and use this in calculations

  • Complete calculations involving energy transfers between gravitational and kinetic energy

  • Define and calculate power

  • Calculate efficiency of energy transfers

3.4 Materials
Image by Nikola Treći

3.4 Materials 

By the end of this topic you should be able to:

  • Define and describe Hooke’s law and how this varies for springs in series and parallel

  • Describe what the force constant for a spring or a wire is and how this can be found experimentally

  • Describe the difference between elastic and plastic deformation and how this is shown on force-extension graphs

  • Describe what is meant by elastic potential energy and calculate this from the equation and graphs

  • Define and calculate; stress, strain and Young’s Modulus and explain what is meant by ultimate tensile strength

  • Describe how you would experimentally find the Young’s modulus of a metal

  • Describe the terms ductile and brittle and how stress-strain graphs look for these materials and polymetric materials

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