Electric Pendulum

1
Electric Pendulum

• TMF 2004
• Gymnasium Eliky Krásnohorské

2
Position of a ball

• Ball isnt at beginning charged.
• The ball hangs at first
• vertically
• slantingly (it doesnt touch of capacitor)
• slantingly (it touchs of capacitor)

3
The ball hangs vertically

• No motion
• Acting forces
• Gravity (Fg)
• Reaction of a thread (Fr)
• Resultant force is zero.

4
The ball hangs slantingly (it doesnt touch of
capacitor)

• Matematic mechanic pendulum
• Acting forces
• Gravity (Fg)
• Reaction of a thread (Fr)
• Friction
• Resultant force isnt zero (Fv).
• Amplitude of oscillation will
• be decreased.

5
Dependences

• Duration of an oscillation for small amplitude
  and small ball is
• For bigger ball we should include energy of
  rotation the ball.
• For bigger amplitude we have to solve
  numerically.

• l - lenght of pendulum
• g - gravitational acceleration

6
The ball hangs slantingly (it touchs of
capacitor)

• Homogenous electric field.
• Acting forces
• Gravity (Fg)
• Reaction of a thread (Fr)
• Electrostatic (Fe)
• Friction
• Resultant force isnt zero (Fv).
• Duration of an oscillation will
• be decreased ball accelerated.

7
Electrostatic force

• The size of electrostatic force is
• This force give energy to the ball and so the
  ball can accelerate.

• r - radius of a ball
• ? - permitivity of enviroment
• U - voltage on the capacitor
• D - distance beetwen plates of capacitor

8
Special efects and measurement

• Discharge of a ball by sparks and brush
  discharge.
• The during of an oscillation was measured by an
  cassete recorder and sound balster on a computer.