The formula in Equation 2 calculates the period of the pendulum. When the period and
the torsion constant are known, the moment of inertia can be calculated, as shown in
Example 1. This makes torsional pendulums useful tools for experimentally determining
the moments of inertia of complex objects.Restoring torque
IJ = íțș
IJ = torque
ț = torsion constant
ș = angular displacement
Units for ț: N·m/rad
Period
T = period
I = moment of inertia
ț = torsion constant
The torsional pendulum has a
period of 3.0 s. What is its
moment of inertia?
I = (0.088 N·m/rad)(3.0 s)^2 /4ʌ^2
I = 0.020 kg·m^2
(^284) Copyright Kinetic Books Co. 2000-2007 Chapter 14