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Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538

Physics Demo Manual

Demonstrations are cataloged according to PIRA Bibliography


Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.

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 Harmonic Motion
  video  - Pendula, Spring and Simple
 Pendula, Conical and Torsional
  video  - Pendula, Physical (Center of Percussion)
 Projected Uniform Circular Motion
 Damped Mass on Spring
  video  - Forced Oscillations
 Hacksaw Blade Resonance
  video  - Resonance Wire Ring
  video  - Inverted Pendulum - Function Generator
 Inverted Pendulum - Reciprocating Saw
 Coupled Pendulum Oscillators
 Coupled Magnetic Oscillations
 Coupled Harmonic Oscillators
 Lissajous Figures on the Scope
 Lissajous Fifures with Laser
 Parametric Amplifier / Oscillator

Hacksaw Blade Resonance


Demonstrates the concept of the natural or resonant frequency of a vibrating system. In particular, shows how the resonant frequency of a rod or ruler depends on its length.


The drill has a bolt in its chuck which has been bent at a right angle causing the apparatus to vibrate when the drill is running. The drill is plugged into a VARIAC so that the speed at which the drill spins and hence the frequency of the vibration of the apparatus can be adjusted. The apparatus can be placed on a piece of foam or a student can be called upon to hold it. As the frequency of vibration is increased, the natural frequency of the longest blade will be reached first and it will begin to vibrate. The other two blades will remain still. Increase the frequency until all three resonances are found.

For a 140V VARIAC we find resonances at:
50V Red
62V Blue
105V Green


  • Variac
  • Hacksaw Blade Apparatus