GCSE Physics (AQA)

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Force-Momentum Equation

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Forces Momentum

Force-Momentum Equation

7:59 Force as Change of Momentum
Spec 4.5.7.3
Previous Force & Change of Momentum Next Momentum & Safety
  • An equation can relate force to the change in momentum.
  • Understanding how to calculate a change in momentum is crucial.
  • Momentum is given by mass times velocity (P = M * V).
  • Change in momentum is the difference between starting and final momentum (P end - P start).
  • This can be expressed as MV - MU, and factorized to M(V - U).
  • Simplified, this is delta P = M * delta V, where delta represents change.
  • Newton's second law states force equals mass times acceleration (F = MA).
  • Acceleration is the rate of change of velocity (A = delta V / delta T).
  • Substituting acceleration in the force equation gives F = M * delta V / delta T.
  • M * delta V is equivalent to delta P, so F = delta P / delta T.
  • This means force equals the change in momentum divided by the time taken.
  • The resultant force determines the rate of change of momentum.
  • At GCSE level, understanding the derivation from F = MA and momentum definition is important.
  • Units: momentum in kg m/s, time in seconds, force in Newtons.
  • Newtons are equivalent to kg m/s��.
  • Example: Calculate average force for a parachutist reducing momentum from 4000 to 600 kg m/s in 1.2 seconds.
  • Steps: Write key values, calculate change in momentum, calculate average force, round answer.
  • Change in momentum: 600 - 4000 = -3400 kg m/s (negative indicates opposite force direction).
  • Average force: 3400 / 1.2 = 2833.33 Newtons.
  • Round to two significant figures: 2800 Newtons.

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