PURPOSE: To show the behavior for a system at resonance.
DESCRIPTION: Because a water balloon has a low natural frequency it is a good system to study directly and visually the frequency response of a resonant system.
A water balloon is suspended by a clamp above a splash gaurd and is poked from below by the head of an alligator clamp connected to a mechanical vibrator. Adjust the frequency of the vibrator to observe the response at the resonance frequency. The resonance frequency is 4.088 Hertz.
Adjust the vibrator frequency below the resonance frequency. The phase is zero between the movement of the balloon and the motion of the poker. This shows that the driver is in phase with the oscillating system for driving frequencies below the natural frequency.
Adjust the vibrator frequency above resonance. The phase of the balloon is opposed to the phase of the vibrator. This shows that the driving force is out of phase with the oscillating system for driving frequencies above the natural frequency of the oscillator.
Adjust the vibrator to match the natural frequency. The phase relationship at resonance shows that motion of the driver is 90 degrees ahead of the motion of the balloon. With an almost imperceptible oscillation of the vibrator the resonance condition causes the balloon to begin to oscillate with a very large amplitude.
EQUIPMENT: Water balloon and vibrator, as photographed.
SETUP NOTES: See the photographs below:
Updated by JZ in 12/11/2006
