AQA A Level Physics

Revision Notes

6.1.5 Centripetal Force

Calculating Centripetal Force

  • An object moving in a circle is not in equilibrium, 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

  •  Centripetal force can be calculated using:

Calculating Centripetal Force equation 1

Centripetal force diagram, downloadable AS & A Level Physics revision notes

Centripetal force is always perpendicular to the direction of travel

  • Where:
    • F = centripetal force (N)
    • v = linear velocity (m s-1)
    • ⍵ = angular speed (rad s-1)
    • r = radius of the orbit (m)
  • 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 showing examples of centripetal force, downloadable AS & A Level Physics revision notes

Worked Example

A bucket of mass 8.0 kg is filled with water is attached to a string of length 0.5 m and tension 7.0 N at the top of the circle.

What is the minimum speed the bucket must have at the top of the circle so no water spills out?

WE - Centripetal force question image, downloadable AS & A Level Physics revision notes

WE - Centripetal force answer image, downloadable AS & A Level Physics revision notes

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