Revision Notes

1.5.3 Unbalanced Forces

Forces & Motion

  • When an unbalanced (resultant) force acts on an object, it can affect its motion in a number of ways:
    • The object could speed up
    • The object could slow down
    • The object could change direction


what-forces-do, IGCSE & GCSE Physics revision notes

A resultant force can cause an object to speed up, slow down or change direction


Extended Only


  • Force, mass and acceleration are related by the following equation:
force = mass × acceleration
f = m × a
  • You can rearrange this equation with the help of the formula triangle:

Force mass acceleration triangle (2), IGCSE & GCSE Physics revision notes

Use the formula triangle to help you rearrange the equation


  • The greater the force, the greater the acceleration (for a given mass)
  • For a given force, the smaller the mass the greater the acceleration


Exam Tip

If you are trying to find the acceleration check that you know both the unbalanced (resultant) force and the mass of the object. If you don’t, you might need to calculate the acceleration using a different equation.


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