### DEFINITION **Velocity (instantaneous velocity)** is the derivative of position with respect to time. If a body's position at time $t$ is $s=f(t)$, then the body's velocity at time $t$ is $ v(t)=\frac{d s}{d t}=\lim _{\Delta t \rightarrow 0} \frac{f(t+\Delta t)-f(t)}{\Delta t} $