• Velocity?and?acceleration? are both?vector? quantities
• An object in?uniform circular motion?is?continuously changing direction,?and therefore is?constantly changing velocity
  • The object must therefore be?accelerating
• This 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

• An object travelling in uniform circular motion has?centripetal acceleration, yet its angular speed (?) is constant
  • This is because speed is a?scalar?quantity, whilst velocity is a vector quantity
  • Therefore, angular speed is the?magnitude?(size) component of angular velocity

• Key ideas to remember:
  • Angular speed (magnitude) stays constant, angular velocity (direction) is constantly changing
  • Angular speed does not change with radius, but linear speed does
  • The object’s centripetal acceleration is always directed?toward the centre?of the circle, and is perpendicular to the object’s velocity at any one time
  • Velocity and acceleration are both defined by a?change in direction, not just a change in the magnitude