# Acceleration

To accelerate means to speed up. The greater the **acceleration**, the greater the change in velocity over a given time.

The **average acceleration** is the rate at which velocity changes:

\[\overline{a}=\dfrac{\Delta v}{\Delta t}=\dfrac{v_f-v_0}{t_f-t_0}\]

where the bar over the acceleration \(a\) means average, \(v\) is velocity, and \(t\) is time.

Acceleration is a vector in the same direction as the change in velocity, Δv. Since velocity is a vector, it can change either in magnitude or in direction. Acceleration is, therefore, a change in either speed or direction, or both.

The “acceleration due to gravity” is also equal to the “gravitational field”. Equivalence of inertial and gravitational mass.

See also