Frahm Resonance Gyroscope
resonant frequency - simple harmonic oscillators - driven oscillations
What it shows:
Simple harmonic oscillators having different resonance frequencies are driven
into oscillation only when the driving frequency matches the resonant frequency.
How it works:
The Frahm resonance gyroscope is a standard piece of equipment
that can be purchased from science supply houses.
1
It consists of a heavy wheel slightly unbalanced, held in a frame to which
seven metal reeds are attached, each having a different vibrational frequency.
The wheel is set in motion by unwinding a string that has been wrapped around
the axle. As the wheel runs down, it sets each reed successively into vibration
as its rotational frequency passes through the resonant frequency of the reed.
Setting it up:
This is a very small demo (designed for small classroom use) and will need a
video camera/monitor to be seen by the audience in a lecture hall. A larger
version using hacksaw-blade oscillators and a motor with an unbalanced wheel,
all mounted on a board, can be assembled if video viewing is unpalatable.
Comments:
It works well and makes the point. A good story to accompany the demo is the
one about the old car that only shimmies and rattles at certain speeds while
cruising down the highway. Rating **
1 Welch No. 3330, $75 (1971)