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Conservation of Angular Momentum

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Check this out (at 4 minutes, 10 seconds):

*Please use this link to watch the video at the appropriate time:

When I first watched this clip, I couldn't believe it... After all, we have always been taught that an object in motion stays in motion unless acted upon by an external force, and I saw no strings attached to Professor Bowley.

As Bowley explains, the phenomenon of his rotations are caused by conservation of angular momentum. We all know and love the conservation of linear momentum (png.latex? m_{1}v_{1} + m_{2}v_{2}=m_{1}), and the conservation of angular momentum can easily be derived by using the translational-to-rotational substitutions found in many of our rotational motion blog posts.

Conservation of angular momentum: png.latex? I_{prof}w_{prof}^{1}+I_{wheel

This equation explains to us why a changing of the direction of the wheel's angular momentum causes a change in the professor's angular momentum. When the wheel is flipped, its angular velocity (and hence angular momentum) is negated. In order to compensate for the change of the wheel's angular momentum, the professor's moment of inertia or angular velocity must change. In this case, he keeps the wheel the same distance from his axis of rotation (keeping his moment of inertia constant) and ends up increasing his angular velocity, causing him to spin.

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Guest

It is pretty amazing. I wonder if there are any practical applications? The former half of the video seems to explain why tops are stable. That sound like a new blog topic!

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