Force & Momentum (Edexcel GCSE Physics)

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Force & Momentum

Higher Tier Only

  • When a force acts on an object that is moving, or able to move, the object will accelerate (or decelerate)
    • This causes a change in momentum

  • More specifically, the force is the rate of change in momentum

Force and momentum equation, downloadable AS & A Level Physics revision notes

  • Δt is the change in time, or the time taken for the force to change
  • Where the change in momentum is defined as

Final momentum – Initial momentum

Δp = mv – mu

  • Where:
    • m = mass in kilograms (kg)
    • v = final velocity in metres per second (m/s)
    • u = initial velocity in metres per second (m/s)

  • Force and momentum are vectors so they can be either positive or negative values

Deriving the Force & Momentum Equation

  • The force and momentum equation can be derived from Newton's Second law and the definition of acceleration

Worked example

A tennis ball hits a racket with a change in momentum of 0.5 kg m/s.For the different contact times, which tennis racket experiences more force from the tennis ball?

WE - Tennis ball contact time answer image, downloadable AS & A Level Physics revision notes

Examiner Tip

Maths Tip: Remember ‘rate of change’ describes how one variable changes with respect to anotherIn maths, how fast something changes with time is represented as dividing by Δt (e.g. acceleration is the rate of change in velocity)More specifically, Δt is used for finite and quantifiable changes such as the difference in time between two eventsWE - Tennis ball contact time content part, downloadable AS & A Level Physics revision notes

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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.