$\underset{\Delta t \rightarrow 0}{Lim}\: \frac{\Delta \theta}{\Delta t}$ = Instantaneous Angular Velocity $(\omega)$
Relation between angular velocity and linear velocity
Mathematical Relation between angular velocity $(\omega)$ and linear velocity$(v)$:
We know that the angular displacement of the particle is
$\Delta \theta= \frac{\Delta s}{r} \qquad(1)$
Where $r$ = The radius of a circle.
Now divide by $\Delta t$ on both side of equation $(1)$
$\frac{\Delta \theta}{\Delta t}=\frac{1}{r} \frac{\Delta s}{\Delta t} $
If $\Delta t \rightarrow 0$, then the above equation can be written as
$\underset{\Delta t \rightarrow 0}{Lim}\: \frac{\Delta \theta}{\Delta t}=\frac{1}{r}\: \underset{\Delta t \rightarrow 0}{Lim} \: \frac{\Delta s}{\Delta t} \qquad(2)$
Where
$\underset{\Delta t \rightarrow 0}{Lim}\: \frac{\Delta \theta}{\Delta t}$ = Instantaneous Angular Velocity $(\omega)$
$\underset{\Delta t \rightarrow 0}{Lim} \: \frac{\Delta s}{\Delta t}$= Instantaneous Linear Velocity $(v)$
Now equation $(2)$ can be written as
$\omega=\frac{1}{r}v$
$v=r\omega$
The above equation shows that linear or tangential velocity depends on the angular velocity and radius of the circular path. This means that if the radius of the circular path increases with the same angular velocity, then the linear velocity will also increase.
$\underset{\Delta t \rightarrow 0}{Lim}\: \frac{\Delta \theta}{\Delta t}$ = Instantaneous Angular Velocity $(\omega)$