著者

佐々木 勝浩

出版者

国立科学博物館

雑誌

Bulletin of the National Science Museum. Series E, Physical sciences & engineering (ISSN:03878511)

巻号頁・発行日

vol.4, pp.31-40, 1981

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The Foucault's Pendulum in the National Science Museum was replaced by a new improved model in January-April 1981. Before that, some theoretical investigation and experiments, such as measurements of the damping rate and elliptical motion were carried out. We have compared two kinds of suspension. One is the "bolt type" in which the upper end of the wire is simply fixed by a bolt. Another is the "knife edge type" in which the wire is suspended by a ring equipped with double knife edges. The measurements of both the damping rate and the elliptical motion of the pendulum showed that the knife edge type is slightly better. In consideration of the result of the experiments, the bob and the wire changed in size and material, and the suspension ring was improved. The length of the new pendulum is 1950 cm, about 50 cm than before, and the new bob was made of stainless steel instead of lead. Stainless steel is less dense than lead but it is more suitable for the precise shaping and fine finish. The new bob is 23 cm in diameter, 3 cm longer than the old one. The writer designed a new suspension ring to increase the rigidity as shown in Figure 4. The formance of new pendulum is almost satisfactory but no remarkable decrease of damping rate and elliptical motion were observed.