Physics Demo Number: 200
Approximate
Run Time: 15 min
Demo Description
Make use of QEC GlassBuster, a function generator, and an amplifier to drive a wine glass at its resonant frequency.
Scientific Principles
Glass objects driven at their resonant frequencies can be made to shatter.
See A.P. French: AJP51(8) page 688 for a nice description of the complexity of this topic.
Equipment
- Glass Buster
- Pasco Function generator
- Amplifier
Equipment Location
[H-6-3]Instructions
A.) The resonant frequency of the glass should have been predetermined and written on bottom of glass.
When a vigorous standing wave of four loops and nodes on the rim of the glass is viewable (under room lighting) from the adjustment of the function generator , then modest sound pressure levels (less than 100 db) seem to suffice to trigger structural failure of the glass.
533 to 540 Hz seems to be a good number for white wine glasses from Libby
Thus the most nearly foolproof way of trying to explode a glass seems to be to
1) Place glass in holder at an angle so that it has 1/4 inch or more clearance from each speaker.
2) Verify seeing a standing wave on the rim under room lighting by running the power up and down (Maximum of 5 or 10 seconds at a time on red VU meter) to the glass.3) Run the power up and down (Maximum of 5 or 10 seconds at a time on red VU meter) to the glass changing frequency 0.1HZ at a time.
B.) Since the glass has had its' resonant frequency labelled, use it.
Once this resonant frequency has been implemented on the glass and fine-tuned at the green level to the point that a standing wave is seen on the rim of the glass
then a short burst up to red level
should explode the glass.
