The Experimental and Historical Foundations of Electricity - Unicamp

A very practical support can be made with thin plastic coffee cups. We make
a small hole at the bottom of the cup and push both legs of a paper fastener
pass through it. The cup is placed with its mouth upward. We fill it with wet
gypsum dough or wet white cement. It will dry in this position. It will be used
with the cup’s mouth facing downward and the paper fastener pointing upward
(Figure 4.14). Because this kind of support will also be used in other electrical
instruments, it is useful to prepare several of these at once. Some experiments
may require as many as 10 support bases.
Figure 4.14: Support for the electric pendulum made of a thin plastic coffee
cup, paper fastener, and gypsum dough.
After this procedure, we place a drinking straw in the shape of the upside
down letter � upon the support. Another alternative is to use two straws,
one set vertically on the support and the other horizontal. The second straw
is attached to the first straw with a second paper fastener. The legs of this
second paper fastener have an angle of 90 o , with one leg vertical and the other
horizontal.
At the free end of the horizontal straw we tie the silk thread with the paper
disk attached to its lower end. This completes the electric pendulum (Figure
4.15).
Experiment 4.5
silk thread
paper disk
Figure 4.15: Electric pendulum with support.
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