Angular Position and Displacement

Angular position θ\theta corresponds to linear position ss

s=rθ,(1)\tag{1} s = r \theta,

where ss is measured from point s0s_0, whose its angular position is θ0\theta_0, along the arc of a circular path with radius rr. Previous equation can also written in following form

Δs=rΔθ,(2)\tag{2} \Delta s = r \Delta \theta,

with Δs=ss0\Delta s = s - s_0 and Δθ=θθ0\Delta \theta = \theta - \theta_0.