These questions are related to \"Rotation of Rigid Bodies about a Fixed Axis\" l

Question

These questions are related to "Rotation of Rigid Bodies about a Fixed Axis" lab exercise.

1- Does the uncertainty in the theoretical value of inertia of a disk account for the discrepancy in the experimental and theoretical values of it?

2- Is it possible to have different values for W_F (work done against friction)? If so, do the differences make physical sense?

3- Discuss why inertia of a ring is so much larger the the inertia of a disk when the bodies are of about the same mass and dimensions. Base your discussion on

I = m_1(r_1)^2 + m_2(r_2)^2 +...+m_n(r_n)^2

( I is for inertia)

4- Is the kinetic energy of the descending mass really negligible campared with that of the rotating objects as claimed above mgh = (8h^2I)/(D^2t^2) + W_F ?
The ratio of the two kinetic enrgies is 1/2 (m v^2)/(1/2 I w^2). This may easily shown to be:

(1/2 m v^2)/(1/2 I w^2) = (m D^2)/(4 I )

by using v = (w D)/2 .

Please answer what you can.

Explanation / Answer

3).

The key is, the closer the mass to the axis of rotation, the easier it is to add angular velocity to the body.For instance, a skater rotates faster when she puts her arms closer to her body.

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