If you are unhappy counting the seconds to time casting the log then use a pendulum (see Figure 10.8). This is a weight (any weight) on the end of a line. Start it swinging and let it settle into its natural rhythm. When it has found its rhythm, the time it takes to swing back and forward once is called its period. How long this takes depends on the length of the string. A one-second pendulum has a string 24.9 cm (9.8 inches) long.
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