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It is not very obvious that a light body
and a heavy one fall at the same speed (ex-
cept for the resistance of the air). Galileo
proved this on paper, but to convince the
world he had to experiment from the lean-
ing tower of Pisa.
At an early age he discovered the princi-
ple of isochronism of the pendulum, which,
in the hands of Huyghens in the middle of
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