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Accurate Clock Pendulums$
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Robert J. Matthys

Print publication date: 2004

Print ISBN-13: 9780198529712

Published to Oxford Scholarship Online: January 2010

DOI: 10.1093/acprof:oso/9780198529712.001.0001

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Effect of the pendulum rod on Q

Effect of the pendulum rod on Q

Chapter:
(p.179) Chapter 26 Effect of the pendulum rod on Q
Source:
Accurate Clock Pendulums
Author(s):

Robert James Matthys

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780198529712.003.0026

A pendulum rod's air drag has a significant effect on the pendulum's Q. Many years ago, an experiment was carried out to determine the effect of bob shape on a pendulum's Q. The results showed that a football-shaped bob, pointed horizontally in the direction of swing, had the highest Q (least air drag) of any bob shape tested. The highest Q shape had a 2:1 length-to-diameter ratio. Spherical bobs had a little lower Q and right circular cylinders, with their cylindrical axis parallel to the pendulum rod's axis, had even lower Q. This chapter describes an experiment to measure the effect of the pendulum rod on Q. The pertinent rod variable is the rod's diameter. The data show that the Q decreases as the rod's diameter increases, and that the pendulum's Q with a spherical bob is 6-20% better than with a cylindrical bob. Better Q means proportionately better timekeeping.

Keywords:   Q, pendulum rod, air drag, bob shape, diameter, spherical bob, cylindrical bob

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