For spins, estimate rotational physics for spins

[erictleung]

User story: As a learner or coach, I want to be able to tell what elements of a skater's body is throwing off the balance of a spin, so that feedback on how to correct and more balance the spin can be given.

Resources:

• https://www.physicsclassroom.com/Physics-Interactives/Balance-and-Rotation
• https://en.wikipedia.org/wiki/Rotating_unbalance
• https://openstax.org/books/physics/pages/6-3-rotational-motion