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GCSE Physics · AQA 8463 · Topic 4.5

Forces

Key points

  • Scalars have size only (speed, distance, mass, energy); vectors have size and direction (velocity, displacement, force, acceleration, momentum).
  • Weight: W=mgW = mg. Work done: W=FsW = Fs. Hooke's law: F=keF = ke.
  • Moments: M=FdM = Fd; for balance, clockwise moments = anticlockwise moments. Pressure: p=FAp = \frac{F}{A}, and in a liquid p=hρgp = h\rho g.
  • Motion: v=stv = \frac{s}{t}, a=Δvta = \frac{\Delta v}{t} and v2−u2=2asv^2 - u^2 = 2as. The gradient of a distance–time graph is speed; of a velocity–time graph, acceleration.
  • Newton's laws: balanced forces mean constant velocity; F=maF = ma; equal and opposite interaction forces.
  • Stopping distance = thinking distance + braking distance.
  • Momentum p=mvp = mv is conserved in a closed system (higher tier).

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Forces explain why things start moving, speed up, slow down, stretch, turn or float. This is the largest topic in the course and carries a lot of marks, much of it in calculations, so practise the equations until rearranging them is…

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Sub-topics

  1. 4.5.1Forces and their interactions
  2. 4.5.2Work done and energy transfer
  3. 4.5.3Forces and elasticity
  4. 4.5.4Moments, levers and gears
  5. 4.5.5Pressure and pressure differences in fluids
  6. 4.5.6Forces and motion
  7. 4.5.7Momentum

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