Advanced Laboratory / Lecture Demonstration Apparatus

Apparatus Title: Shattering the Wineglass

Abstract: A wineglass will be acoustically driven to determine its resonant frequency and observe its physical variations at low energy levels. The wineglass will then be driven to larger levels until its elastic limits are exceeded and failure rapidly occurs.

Other support needed for the proper operation of this apparatus:

Description: The Driver: The master oscillator generates a sine wave signal into a 100-Watt solid state P.A. amplifier which drives a speaker horn through a 2" diameter brass tube 3mm from the cup. Resonance: The vibration of the wineglass is detected by a piezo-ceramic device located on an oscilloscope. The resonant frequency is determined then as the master oscillator sweeps a frequency range generally from 300-1300 Hz. This process can be shown on the monitor or projector via a camera mounted in front of the oscilloscope. Observed Resonance: In addition to the observed resonance peak on the oscilloscope, the motion of the wineglass rim (which has been painted white) is observed with the aid of an array of diffused LEDs illuminating the rim at a strobe rate about ±3 Hz from the resonant frequency of the glass. This strobe diode array is visually displayed on the viewing monitor via a camera mounted close to the array. The resonant vibration can also be clearly heard and felt by touching the rim with the top of a fingernail or the edge of a wooden pencil. Shattering: Once the exact resonance frequency of the glass is found and observed, the wineglass can be easily broken by turning up the volume (gain) of the amplifier at a rapid rate. A video tape made with a third camera focused on a whole side view of the glass may be replayed at slow speeds to glimpse a limited number of video frames of the event.

Safety Notes:

• 1. A Watt meter is connected to the P.A. amplifier to help monitor the ambient acoustic conditions.
• 2. A "good" wineglass will resonate visually very nicely at 0.01-0.1 Watt and shatter at 1 to 5 Watts, while poorer quality glasses will require much higher dB levels.
• 3. The demonstrator wears ear protection while doing the demonstration especially during the shattering phase. The audience is encouraged to cover their ears at any stage where the audio becomes uncomfortable especially when the demonstrator announces his intention to begin the shattering phase.

Equipment Notes: ·

• Master oscillator - Pasco P1-9587C Digital Generator-Amplifier ·
• Power amplifier - 100-Watt Solid State P.A. Amplifier (Radio Shack) ·
• Horn driver - 100-Watt ·
• Strobe driver - same as Master Oscillator ·
• Piezo detector - piezo-ceramic transducer (Radio Shack), epoxied to fiber-board plate with a 1/8" sorbothane on top and sorbothane feet beneath ·
• Resonance oscilloscope - Telequipment 561 ·
• Cameras - black and white DDC (Watec) ·
• Video switch - Radio Shack audio/video selector ·
• Wineglass - 24% lead oxide crystal (Sélection by Cristal d'Arques - France, available at the Hudson's Bay Company in Canada)