Circular Motion (Edexcel GCSE Physics: Combined Science)

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:

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

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 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 Table