GCSE Physics (AQA)

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Calculating Weight

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Forces Forces and their interactions

Calculating Weight

3:03 Vectors and Weight
Spec 4.5.1.3
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  • Gravitational field strength measures the strength of gravitational force from an object at a certain point.
  • Gravitational force is the attraction between two objects with mass.
  • Earth's surface gravitational field strength is 9.8 newtons per kilogram.
  • This value is provided in exams and doesn't need to be memorized for GCSE.
  • Gravitational field strength is weaker for smaller objects or at points far from the object.
  • Field strength decreases with distance and is weaker on the moon due to its smaller mass compared to Earth.
  • Weight of an object is the product of its mass and the gravitational field strength.
  • Weight is the gravitational force acting on an object.
  • Weight equals mass multiplied by gravitational field strength.
  • Field strength is assumed constant near the surface due to negligible height changes.
  • Weight is proportional to mass when field strength is constant, applicable at a planet's surface.
  • Equation: Weight (W) = Mass (M) x Gravitational Field Strength (G).
  • Weight is measured in Newtons, mass in kilograms, and field strength in Newtons per kilogram.
  • Example: On Mars, a 5 kg ball has a weight of 20 Newtons.
  • To calculate Mars' gravitational field strength:
  • Mass = 5 kg, Weight = 20 Newtons.
  • Rearrange equation to make field strength the subject.
  • Gravitational field strength = Weight / Mass.
  • Substitute values: 20 Newtons / 5 kg = 4 Newtons per kilogram.

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