Mass, Weight & Gravitational Field Strength (Edexcel International A Level Physics)

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Lindsay Gilmour



Mass, Weight & Gravitational Field Strength


  • Mass is the measure of the amount of matter in an object
    • Consequently, this is the property of an object that resists change in motion
  • The greater the mass of a body, the smaller the change produced by an applied force
    • The SI unit for mass is the kilogram (kg)


  • Weight is the force a body experiences due to being in a gravitational field, it is given by the equation

W = mg

  • Where
    • m = mass (kg)
    • g = gravitational field strength (N kg−1)

Gravitational Field Strength

  • Gravitational field strength is the force per kilogram that acts on an object, it is found using the equation

  g = F over m

  • Where
    • F = weight (N)
    • m = mass (kg)
  • On the Earth's surface the average gravitational field strength = 9.81 N kg−1

Constant Acceleration in Freefall

  • Freefall is used to describe falling objects where the only force is weight
    • Drag forces are ignored
    • By considering freefall we can see that all objects must fall with exactly the same value for acceleration, regardless of their mass or weight


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Lindsay Gilmour

Author: Lindsay Gilmour

Lindsay graduated with First Class Honours from the University of Greenwich and earned her Science Communication MSc at Imperial College London. Now with many years’ experience as a Head of Physics and Examiner for A Level and IGCSE Physics (and Biology!), her love of communicating, educating and Physics has brought her to Save My Exams where she hopes to help as many students as possible on their next steps.

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