Acceleration

Acceleration is the rate of change of velocity. It is a vector quantity with both magnitude and direction.

$a = \frac{\Delta v}{t} = \frac{v - u}{t}$

An object accelerates when it speeds up, slows down, or changes direction. Deceleration is acceleration in the opposite direction to the velocity.

The SI unit is m/s$^2$. A value of 2 m/s$^2$ means the velocity increases by 2 m/s every second.