Here's why:

* Radians per second (rad/s): This is the standard unit for angular velocity in physics. A radian is a unit of angle, representing the ratio of the arc length of a circle to its radius. Therefore, radians per second measures how many radians an object rotates through each second.

* Revolutions per minute (rpm): This is a more practical unit used in everyday contexts. One revolution is a complete circle (360 degrees or 2π radians). Revolutions per minute tells you how many times an object spins around its axis in a minute.

Note: While both units are commonly used, radians per second is preferred in physics and engineering due to its compatibility with other units and formulas.

Let me know if you'd like to know more about angular velocity or any other related concepts!