Centripetal Force (AQA A Level Physics): Revision Note

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 force towards the centre of the circle required to keep a body in uniform circular motion.

• It is always directed towards the centre of the body's rotation

•  Centripetal force can be calculated using:

$F=\frac{m{v}^2}{r}=mr{\omega }^2=mv\omega$

• Where:

  • $F$ = centripetal force (N)

  • $m$ = mass (kg)

  • $v$ = linear velocity (m s^-1)

  • $\omega$ = 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

• When solving circular motion problems involving one of these forces, the equation for centripetal force can be equated to the relevant force equation

• For example, for a mass orbiting a planet in a circular path, the centripetal force is provided by the gravitational force

• When an object travels in circular motion, there is no work done

  • This is because there is no change in kinetic energy