1. What is the usual shape of the bob of a clock pendulum? Why is this shape used instead of a sphere?
2. Removing the bob from a clock pendulum has what effect on its motion? Also on the motion of the hands?
3. How does the expansion of the rod of a pendulum in summer and its contraction in winter affect the keeping of time by a clock? How can this be corrected?
4. Master clocks that control the time of a railway system have a cup of mercury for a bob. This automatically keeps the same rate of vibration through any changes of temperature. How?
5. How will the length of a seconds pendulum at Denver, 1 mile above sea-level, compare with one at New York? Why?
Fig. 82—Escapement and pendulum of a clock.
6. What is the period of a pendulum 9 in. long? Note. In problems involving the use of the third law, use the length of a seconds pendulum for l, and call its period 1.
7. A swing is 20 ft. high, find the time required for one swing across the arc.
8. A pendulum is 60 cm. long. What is its period?