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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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Pendulum air movement: A second try

Pendulum air movement: A second try

(p.195) Chapter 29 Pendulum air movement: A second try
Accurate Clock Pendulums

Robert James Matthys

Oxford University Press

Air drag is the biggest energy loss in a pendulum. The bob generates most of the air drag because of its large size and its location at the end of the pendulum rod. In this chapter, the movement of air around four different pendulum bobs is shown by white smoke in a series of pendulum photographs. The photos provide general information on airflow around the pendulum bob, but not much specific information that can be used to reduce the air drag and the pendulum's energy losses. Changing from a cylindrical to a spherical bob shape will reduce the energy losses and improve the pendulum's Q by 6-20%. But it takes about twice as much material (doubling the cost) and about four times as much effort to make a spherical bob as it does to make a cylindrical one. The best solution is to operate the clock in a vacuum chamber, although vacuum chambers have problems of their own.

Keywords:   air drag, air movement, pendulum, bob, white smoke, photographs, airflow, energy loss, vacuum chamber

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