Question

Angular momentum L in a rotating system is defined as L = I? (moment of inertia times angular speed). If there are no external forces changing the rotation (a force that changes rotation is a called a torque), then the total angular momentum of the system remains constant. In other words, raising or lowering one value (I or ?) makes the other change accordingly, because their product remains constant. Watch the YouTube video linked below. Ice skaters always go into a spin with arms (and in this case a leg) extended. This makes their I fairly large. How fast is she spinning? What does she do next, and what happens to angular speed? Finally, find another case of the conservation of angular momentum and describe or link it here.

https://www.youtube.com/watch?v=AQLtcEAG9v0

Answer 1

In the video the Ice skater Natalia Kanounikov goes into a spin with her arms and one leg extended. This increases the inertia of her body thus the angular velocity is less. This helps her to get into a comfortable position maintiing her balance. Then she brings her arms and leg close the her body(Axis of rotaion) thus reducing the moment of inertia I. As a result her angular velocity increases due to law of conservation of moment and she starts spinning very fast. She attains a maximum speed of 308RPM(rotations per minute).

Below is another link displaying conservation of angular momentum: https://www.youtube.com/watch?v=FmnkQ2ytlO8