Here's why:

* Angular displacement: Measured in radians (rad), which represents the change in angle.

* Angular velocity: Measured in radians per second (rad/s), representing the rate of change of angular displacement.

* Angular acceleration: Measured in radians per second squared (rad/s²), representing the rate of change of angular velocity.

Therefore, the unit for angular acceleration is the unit of angular velocity divided by the unit of time, resulting in rad/s².