Regents Physics

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Regents Physics
The Simple Pendulum
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What is a Simple Pendulum?

• A simple pendulum consists of a bob or mass
  attached to a string of negligible mass

?
l
m
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Where do we find pendulums?

• We typically find them in clocks
• Very minimal friction
• Good for showing conservation of energy

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The Foucault Pendulum
Originally designed to measure the rotation of
the Earth
At either the North Pole or South Pole, the
plane of oscillation of a pendulum remains fixed
with respect to the fixed stars while Earth
rotates underneath it, taking one sidereal day
to complete a rotation. So relative to Earth,
the plane of oscillation of a pendulum at the
North or South Pole undergoes a full clockwise or
counterclockwise rotation during one day,
respectively. When a Foucault pendulum is
suspended on the equator, the plane of
oscillation remains fixed relative to Earth. At
other latitudes, the plane of oscillation
processes relative to Earth, but slower than at
the pole the angular speed,
Animation of a Foucault pendulum, with the
rotation rate greatly exaggerated. The green
trace shows the path of the pendulum bob over
the ground, and the blue trace shows the path in
a frame of reference rotating with the plane of
the pendulum.
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Variables Involved

• Period (T) The time required for the displaced
  pendulum to complete one cycle of motion
  measured in seconds
• Frequency (f) The number of cycles per second
  measured in hertz (Hz)
• Frequency 1/T
• Both are independent of mass
• Amplitude is displaced angle of distance

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Pendulum Equation
l g
T 2?
This equation holds for amplitudes of less than
15 degrees
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Energy in a Pendulum
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Pendulum Practice Problem
Calculate the length of a pendulum that posses a
2-second period and is displaced 15 from vertical
2) Choose Equation
1) Write knowns/unknowns
T 2 s
g 9.8 m/s2
3) Rearrange and solve
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