# Turning & circular motion

Turning requires sideways acceleration, perpendicular to the velocity’s direction. This acceleration is called centripetal or radial acceleration; typically symbolised $a_\perp$, $a_{cen}$ or $a_{rad}$.

Keeping $a_\perp$ constant causes circular motion (as driving in a roundabout). If the speed $v$ is constant (no parallel acceleration), the circular motion is called uniform and the following expression holds true:

$$a_\perp=\frac{v^2}r$$

$r$ is the radius of the circular path.