In a similar way we can relate the angular velocities of the mass at times separated
by time δt, i.e. the new velocity will be different from the old value by an amount
equal to δt × ¨ θ(t), where ¨ θ(t) is the angular acceleration (cf. the familiar expression
v = u + at for linear motion). The acceleration also varies with time and so again
we will use its average value during the time interval δt. For the evaluation of
˙ θ(t + δt/2) this translates to