Here's why:

* Angular Displacement: Angular displacement is the change in angle of an object, measured in radians.

* Time: Time is measured in seconds.

* Angular Velocity: Angular velocity is the rate of change of angular displacement over time. Therefore, it's measured in radians per second.

Other units for angular velocity:

While radians per second is the standard unit, you might occasionally encounter other units, such as:

* Degrees per second (°/s)

* Revolutions per minute (rpm)

However, it's important to convert these units to radians per second for most calculations and physical equations.