To prevent the swings
twisting, they are best made of strong wire bent as shown in Fig. 148, care
being taken that the sides are of equal length, so that both hooks may
press equally on the strings. Eighteen inches is a good length. The longer
the swing, and the heavier the weight, the longer will the experiment last.
The swings are hung, six inches apart, from a stout string stretched
tightly between two well-weighted chairs or between two fixed points. The
string should be at least 4 feet long.
With two equally long and equally weighted pendulums, the three following
experiments may be carried out:--
1. Let one, A, start from rest. The other, B will gradually die, and A
swing to and fro more and more violently, till B at last comes to a dead
stop. Then A will die and B in turn get up speed. The energy originally
imparted to B is thus transferred through the string from one pendulum to
the other an indefinite number of times, with a slight loss at every
alternation, until it is finally exhausted by friction.
2. Swing them in opposite directions, but start A from a higher point than
B.
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