Two spheres look identical and have the same mass. However, one is hollow and the other is solid. Describe an experiment to determine which is which.

Short Answer

Expert verified

The sphere with larger rotational inertia is hollow, and the smaller rotational inertia is a solid sphere.

Step by step solution

01

Variables on which the MOI of an object depends 

The object's moment of inertia may be determined by evaluating the value of the object’s mass and radius. Its value is directly related to the mass of the object.

02

Experiment describes which sphere is solid and hollow

Two spheres look alike, one is solid, and the other is hollow. Rotate each on the table. The sphere which rotates at a lower rate will be the hollow sphere. It is because, in a hollow sphere, the air inside seeks to get apart from the axis of revolution. Hence, the MOI of the hollow sphere increases.

The expression for the torque is as follows:

\(\tau = I\alpha = {\rm{constant}}\)

Here, \(I\) is the moment of inertia, and \(\alpha \) is the angular acceleration.

Thus, the hollow sphere will spin with smaller angular acceleration.

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FIGURE 8-50

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