The period T of a physical pendulum is measured about a certain pivot point A. T

ID: 2097221 • Letter: T

Question

The period T of a physical pendulum is measured about a certain pivot point A. The

measurement is repeated, varying the locations of the pivot point but keeping the rotations of the

pendulum always in the same plane. The moment of inertia of the object about its center of mass

is ICM, the mass is M, and the distance from the pivot point to the CM is d.

a) Find the period as a function of ICM, M, d, and the acceleration due to gravity (g). Note

that as the pivot point is varied, pivot points that are the same distance from the CM give the

same period.

b) Furthermore, show that, in general, for a given value of T, there are two distances d1 and

d2 that give the same period of oscillation.

c) Show that the moment of inertia of the object about its center of mass and the period can

be expressed as ICM = Md1d2 and T = 2pi * sqrt ( d1+ d2 /g) respectively.

d) [DIFFICULT] Show that the smallest period for rotations occurs when the distance of

the CM from the pivot is d = sqrt ( Icm / M )

sqrt 64x/cm

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