IIT (NTSE/Olympiad)  

Circular Motion & Rotational Dynamics

1. Angular Displacement

1. Angular displacement
Introduction : Angle subtended by position vector of a particle moving along any arbitrary path w.r.t. some fixed point is called angular displacement.

(a) Particle moving in an arbitrary path

(b) Particle moving in straight line

(c) Particle moving in circular path
(i) Angular displacement is a vector quantity.
(ii) Its direction is perpendicular to plane of rotation and given by right hand screw rule.
Note: Clockwise angular displacement is taken as negative and anticlockwise displacement as positive.

(iii) For circular motion ΔS = r × Δq
(iv) Its unit is radian (in M.K.S)
Note : Always change degree into radian, if it occurs in numerical problems.
Note : 1 radian = ⇒ π radian = 180°
(v) It is a dimensionless quantity i.e. dimension [M0L0T0]

IIT (Class X)