**Angular Displacement ****θ**The angle θ, through which the object has moved is known as its angular displacement.

θ=arc/radius = s/r

**Radian**

One radian (rad) is defined as the angle subtended at the center of a circle by an arc equal in length to the radius of the circle.

1 rad = 57.3^{0}

**Angular Speed ****ω**

The angular speed is defined as the rate of change of angular displacement.

Angular speed ω = Δθ/Δt

**Centripetal force**

Centripetal force is the name given to that force which causes a change in direction of velocity toward the center of the circular motion. It is the net force that acts on an object to keep it moving along a circular path.

The figures shows the angle between two radii OA and OB and V_{A} and V_{B}.

So,

DE/CD = AB/OA

ΔV/V_{A }= Δs/r

ΔV= Δs (V_{A }/r)

Dividing both sides by Δt

ΔV/Δt = (Δs/Δt) (V_{A}/r)

A= v^{2}/r

Centripetal force = mv^{2}/r = mrω^{2}