Circular Motion (Edexcel GCSE Physics)

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Circular Motion

Higher Tier Only

  • Velocity is a vector quantity, and the velocity of an object is its speed in a given direction
  • When an object travels along a circular path, its velocity is always changing
    • The speed of the object moving in a circle might be constant - that is, it is travelling the same distance every second
    • However, the direction of travel is always changing as the object moves along the circular path

  • This means that an object moving in circular motion travels at a constant speed but has a changing velocity
  • The image below shows an example of a famous object that moves in a circular path with a constant speed but changing direction:

ISS circular dance, downloadable IGCSE & GCSE Physics revision notes

The International Space Station’s velocity is always changing - it whizzes around the Earth at a constant speed of about 7660 m/s but is always changing direction

Examiner Tip

You may be asked to explain why motion in a circle involves constant speed but changing velocity, so remember to mention that velocity is a vector quantity, so both magnitude and direction are important.Even though the magnitude (speed) doesn’t change, its direction does - so the velocity itself is changing.

Centripetal Force

Higher Tier Only

  • An object moving in a circle is not in equilibrium as it has a resultant force acting upon it
    • This is known as the centripetal force and is what keeps the object moving in a circle

  • The centripetal force (F) is defined as:

The resultant perpendicular force towards the centre of the circle required to keep a body in uniform circular motion

  • The centripetal force is shown by the arrow labelled F in the diagram below:

Centripetal Force GCSE, downloadable IGCSE & GCSE Physics revision notes

Centripetal force is always perpendicular to the direction of travel and is directed towards the centre of the circle

  • Note: centripetal force and centripetal acceleration act in the same direction
    • This is due to Newton’s Second Law

  • The centripetal force is not a separate force of its own
    • It can be any type of force, depending on the situation, which keeps an object moving in a circular path

Examples of Centripetal Force TableTable showing examples of centripetal force, downloadable AS & A Level Physics revision notes

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.