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This qualitative film was designed
for students to study conservation of energy. A pole vaulter
(mass 68 kg, height 6 ft) is shown first at normal speed and
then in slow-motion as he clears a bar at 11.5 feet. Measure
the total energy of the system at two times just before the
jumper starts to rise, and part way up when the pole has a
distorted shape. The total energy of the system is constant,
although it is divided up differently at different times.
Since it takes work to bend the pole, the pole has elastic
potential energy when bent. This elastic energy comes from
some of the kinetic energy the vaulter has as he runs
horizontally before inserting the pole into the socket.
Later, the elastic potential energy of the bent pole is
transformed into some of the jumper's gravitational
potential energy when he is at the top of the
jump.
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