BAR PENDULUM: A pendulum can be used to measure the acceleration of gravity g because its period of swing T depends only on g and its length L T = 2pi*SQRT OF L/g So by measuring the length L and period T of a pendulum, g can be calculated. The accuracy of g measurements was limited by the difficulty of measuring the other factor L, the length of the pendulum, accurately. L was the length of an ideal simple pendulum consisting of a point mass swinging on the end of a massless cord. However the length of a real pendulum, a swinging rigid body, known in mechanics as a compound pendulum, is more difficult to define. A real pendulum had the same period as a simple pendulum with a length equal to the distance between the pivot point and a point called the center of oscillation, which is located under the pendulums center of gravity and depends on the mass distribution along the length of the pendulum. The problem was there was no way to find the location of the center of oscillation in a real pendulum accurately. It could theoretically be calculated from the shape of the pendulum if the metal parts had uniform density. In a real pendulum,If the wire had negligible mass, the center of oscillation was close to the center of gravity of the sphere. But even finding the center of gravity of the sphere accurately was difficult. In addition, this type of pendulum inherently wasnt very accurate. The sphere and wire didnt swing back and forth as a rigid unit, because the sphere acquired a slight angular momentum during each swing. Also the wire stretched elastically during the pendulums swing, changing L slightly during the cycle.
Posted on: Sat, 08 Mar 2014 03:13:47 +0000
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