# While using equations of circular motion why do we need to express all

1. Sep 4, 2011

### Shivam123

while using equations of circular motion why do we need to express all angles in radians?

2. Sep 4, 2011

### BruceW

Re: kinematics

$s = r \theta$ (i.e. arc-length equals radius times angle) is only true when the angle is expressed in radians.
In other words, we know that $\pi$ is a special number, such that the circumfrence equals $2 \pi r$ for any circle. And so we use radians to make use of this special number.

3. Sep 4, 2011

### Shivam123

Re: kinematics

good..got it thanks