How Does Changing the Wheel's Axis Affect Platform Rotation?

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The discussion focuses on the conservation of angular momentum when a person on a frictionless rotating platform changes the orientation of a spinning bicycle wheel. The initial confusion arises from the belief that angular momentum should be conserved in both vertical and horizontal axes, despite the lack of external forces. It is clarified that the platform is only allowed to rotate about a vertical axis, which constrains the system. The key point is that while the horizontal angular momentum may not be conserved due to this constraint, the vertical angular momentum remains conserved. Understanding these dynamics is crucial for solving the problem effectively.
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Homework Statement



A person stands on a platform, initially at rest, that can rotate freely without friction. The moment of inertia of the person plus the platform is IP. The person holds a spinning bicycle wheel with its axis horizontal. The wheel has a moment of inertia Iw and angular velocity WW. What will be the angular velocity WP of the platform if the person moves the axis of the wheel so that it points vertically upward?

Homework Equations


[/B]
L_initial = L_final

The Attempt at a Solution



I didn't understand why the angular momentum is conserved only in vertical axis. There is no external force, so what has happened to angular momentum in the horizontal? Wıth regard to what should I choose an axis so that I can apply the conservation?
 
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hitemup said:
There is no external force, so what has happened to angular momentum in the horizontal?
External forces do come into play to prevent the platform from rotating horizontally. The platform is constrained to freely rotate only about a vertical axis.
 
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