All courses › Foundations of Physics › Velocity and acceleration

Velocity and acceleration

The velocity tells you how much the position changes per unit time, and the acceleration tells you how much the velocity changes per unit time. Both can be positive or negative for motion along a straight line: the sign shows the direction relative to the one you chose as positive.

\bar v = \dfrac{\Delta s}{\Delta t}

average velocity

a = \dfrac{\Delta v}{\Delta t}

acceleration

Symbols

$s$	position/displacement	m
$v$	velocity	m/s
$a$	acceleration	m/s²
$t$	time	s

Example

A runner moves from $s = 0$ to $s = 100$ m in $12.5$ s. The average velocity is $\bar v = 100/12.5 = 8.0$ m/s.

The same sign on

a

and

v

means the speed is increasing; opposite signs mean it is slowing down.

Practise motion for free →

← Measurement uncertainty · Equations of motion →

Part of Foundations of Physics: Motion.