![]() To determine the period, measure the total time of 100 swings of the pendulum. Find the positions before and mark them on the rod. Adjustment of the positions of the knife edges and masses until the two periods are equal can be a lengthy iterative process, so don't leave it 'till lecture time. A 3/4" square × 18" long 4 steel bar is supplied for this purpose. Rather than measure the distance between the two knife edges, it is easier to adjust them to a predetermined distance. Setting It UpĪs in the Physical Pendulum demo, the pendulum knife-edge support is a U-shaped piece of aluminum that is clamped onto a standard lab bench rod. Therefore, all other corrections and systematic errors aside, in principle it is possible to measure g to better than 0.2%. By timing 100 or more swings, the period can be determined to an accuracy of fractions of a millisecond. A digital wristwatch or large analog timer 3 is used to verify the period. The distance between two knife edges can be measured with great precision (☐.05cm is easy). The period for this arrangement can be proved 2 to be the same as that of a simple pendulum whose length L is the distance between the two knife edges. The Kater's pendulum used in the instructional laboratories is diagramed below and its adjustments are described in the Setting It Up section. Two knife-edge pivot points and two adjustable masses are positioned on the rod so that the period of swing is the same from either edge. To overcome this difficulty we can turn a physical pendulum into a so-called reversible (Kater's) 1 pendulum. ![]() For example, it's hard to estimate where exactly the center of the mass is. The value of T can be obtained with considerable precision by simply timing a large number of swings, but comparable precision in the length of the pendulum is not so easy. Using a simple pendulum, the value of g can be determined by measuring the length L and the period T. By adding a second knife-edge pivot and two adjustable masses to the physical pendulum described in the Physical Pendulum demo, the value of g can be determined to 0.2% precision. ![]() What It ShowsĪn important application of the pendulum is the determination of the value of the acceleration due to gravity. A physical pendulum with two adjustable knife edges for an accurate determination of "g". ![]()
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