Radian
The angle subtended at the centre of a circle by an arc of length equal to the radius of the circle
Angular displacement
The angle of arc through which the object has moved from its starting position
Angular speed
The angular displacement over unit time
Centripetal force
The resultant force on an object towards the centre of the circle, when the object is rotating round that circle at a constant speed.
Centripetal acceleration
The acceleration of an object towards the centre of the circle, with a constant speed