Having already learned about momentum and the conservation of momentum, my class recently learned about angular, or rotational, momentum. To understand rotational momentum, you must first know about rotational inertia. Rotational inertia is the property of an object to resist changes in spin (rotation). The more mass an object has, the greater its rotational inertia is. This also involves the distribution of the mass. When the mass of an object is far away from the axis of rotation, the rotational inertia is greater. When the girl in the video is starting to spin, she keeps her arms extended. This causes her mass to be spread out from her body, where her axis of rotation is, so she spins slowly at first. When she pulls her arms and legs into her body, this changes the distribution of mass so that it is closer to the axis of rotation. She then has a smaller rotational inertia and spins very quickly.
But wait, there's more...
Just as linear momentum is conserved, there is conservation of rotational momentum as well. The total rotational momentum of an object before the change in spin must be equal to the total rotational momentum of the object after the change in spin. Rotational momentum is equal to rotational inertia x rotational velocity. In the video, we could see how the girl's rotational inertia changed (which I explained) and how it directly affected her velocity. Before the change in her spin, she had a large amount of rotational inertia and a subsequently small rotational velocity. After the change in spin, her rotational inertia was much smaller, and in accordance with conservation of rotational momentum, her rotational velocity increased so that the total momentum was the same before and after the change in spin.
I think this video clearly shows the change. The demonstration would be perfect if there were arrows showing her inertia and such, but I think this is a great rotational momentum resource when coupled with an explanation.
I thought that your video choice was perfect for what we are learning about in Physics. Also I felt like you left a very nice detailed description that really helped me to further my understanding of angular momentum. I thought that the way you wrote your description was very engaging and really well written. You did a great job referring back to the video when you explained a concept. This allowed the viewer to see this physics concept in action. It is hard to think of constructive criticism, because I think that this blog post was spot on. The only thing I think you could do to make it better, is talking more about the video. I really enjoyed this blogpost, whoot whoot go Cori.
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