Mechanics

Kinematics

Average velocity

\bar{\upsilon}=\frac{\Delta x}{\Delta t}

Velocity

\mathbf{v} = \frac{d \mathbf{x}}{dt}

or

\mathbf{v} = \mathbf{i}\frac{d{x}}{dt} + \mathbf{j}\frac{d{y}}{dt} + \mathbf{k}\frac{d{z}}{dt}