Revision Notes

1.3.1 Mass & Weight

Mass & Weight: Basics

  • Mass (measured in kilograms, kg) is related to the amount of matter in an object
  • Weight (measured in newtons, N) is the force of gravity on a mass
  • The size of this force depends on the gravitational field strength (often called gravity, g, for short)
weight = mass x gravitational field strength
W = m x g

  • You can rearrange this equation with the help of the formula triangle:

mg-triangle, IGCSE & GCSE Physics revision notes

Use the formula triangle to help you rearrange the equation


  • The value of g (the gravitational field strength) varies from planet to planet
  • On Earth:

Gravitational field strength diagram, IGCSE & GCSE Physics revision notes

Diagram showing the gravitational field strengths of the planets in our solar system


  • The weight (and hence mass) of two objects can be compared using a balance


Types of balance, IGCSE & GCSE Physics revision notes

A balance can be used to compare two different weights


Exam Tip

  • Mass is usually measured in kilograms in Physics. If it is given in grams, you might need to convert to kilograms by dividing the mass by 1000
  • It is easy to confuse mass and weight. – take care to use each term appropriately
  • When referring to the force of gravity:
    • be careful to call it weight, gravitational force or gravitational attraction
    • Don’t refer to it as just gravity and certainly don’t call it gravitational field strength or gravitational potential (both of which mean different things)


Extended Only

The Significance of Mass

  • Mass has two significant effects in Physics:
    • The mass of an object’s opposed any attempt to change that object’s motion
      The greater the mass of an object, the more difficult it is to speed it up, slow it down or change its direction
      This property of mass is sometimes referred to as inertia
    • Mass is also the source of an object’s weight – the force of gravity on a mass
      The greater the mass, the greater the weight

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