Angular momentum is the relationship between Rotational Inertia and Rotational Speed. More simply, it is the tendency an object has to continue moving in a circle or spinning.
Angular Momentum = Angular Velocity x Rotational Inertia
When a figure skater pulls their arms closer to their body, they are reducing their Rotational Inertia, making themselves more aerodynamic. In order to sustain this and maintain their momentum, the Rotational Speed must increase.
Angular momentum is basically an object’s resistance to a change in rotation. To change an object’s motion, force must be applied, since objects in motion tend to stay in motion. This force is called torque when relating to rotational motion (Torque = Force x Perpendicular Distance from Axis). When torque is applied, the angular momentum increases, then decreases due to friction. But on the ice, there is barely any friction, and the skater can sustain their momentum for long periods of time.
Rotational Inertia requires the object to rotate around its axis as opposed to how an object would behave when traveling in a Straight Motion path. This must be taken into account when an equation is being formulated.
Let Rotational Inertia equal I
Let Mass equal M
Let Distance (from axis) equal R
The Rotational Inertia of an object rotating around an axis can be represented by:
I = mr2
Rotational Inertia is directly correlated to the distance of the object from the axis. If you double the distance of the mass (the rotating object) from the axis, you quadruple the Rotational Inertia. This is why such a minute alteration in the skater’s form can have such drastic effects on their rotational speed.
Rotational Speed is the second variable in Rotational Motion. It is also known as Angular Velocity. It is the rate of rotations and can be represented in revolutions/minute (RPM) and radians/second.
2π radians = 1 rotation
This means that one complete revolution per second is equal to 2π radians/second.
Angular Momentum - Continued
Now that we have our...