# 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

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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