AQA A Level Physics

Revision Notes

6.1.1 Circular Motion

Circular Motion

  • Velocity and acceleration are both vector quantities
  • An object in uniform circular motion has a constant linear speed
  • However, it is continuously changing direction. Since velocity is the speed in a given direction, it, therefore, has a constantly changing velocity
    • The object therefore must be accelerating
    • This is because acceleration is defined as the rate of change of velocity
  • This acceleration is called the centripetal acceleration and is perpendicular to the direction of the linear speed
    • Centripetal means it acts towards the centre of the circular path

Force and acceleration direction, downloadable AS & A Level Physics revision notes

Centripetal force and acceleration are always directed towards the centre of the circle

  • The centripetal acceleration is caused by a centripetal force of constant magnitude that also acts perpendicular to the direction of motion (towards the centre)
  • Therefore, the centripetal acceleration and force act in the same direction

Exam Tip

  • The linear speed is sometimes referred to as the ‘tangential’ speed
  • A tangent is a straight line which touches a circle or curve at exactly one point
  • The key feature of a tangent of a circle is that it always acts perpendicular to its radius
  • You can find out more in the A Level Maths revision notes on Tangents
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