-The Demos-

- The original intent of this demonstration was to shatter a wine glass with sound waves. Although the setup is relatively simply and straight forward, it proved extremely difficult to provide the necessary volume and pitch intensity to actually cause the glass to shatter. There was some resonating of the glass visible, but that's as far as I was able to go. It is unfortunate because of the great visual that this would've provided had this worked. It can still be demonstrated how the resonant frequency of a wine glass can be found (by 'pinging' it, or rubbing the rim with moisture in circles). The process is still interesting to note, but obviously, is not too effective when the glass does not end up shattering all over a lab bench to the pleasure of the students.

- The first of the demos involves a simple pendulum system. It can be made in any way, as long as there are three weights hanging from a supported pole of some sort. The idea here is to display the resonant frequency of a physical system, and a pendulum system is a very simple example to understand. Two of the weights should have the same length of string attatched to the bar, with the third having a smaller length. When one of the weights is driven into motion, it will force the second weight of the same string length to begin to move as well, because they have the same resonant frequency. In this case, only the length of string determines the resonant frequency. The third weight with the small string will not move much at all. It is a simple way to show that systems 'want' to be driven at their resonant frequencies.

- The next demo involves resonance frequency pitch. Two tuning forks are used to demonstrate again, driving systems at resonant frequency. If one tuing fork is struck, and held next to another tuning fork of the same pitch and dimensions, the sound wave itself will drive the frequency of the other tuning fork into resonance, and create a sound; the same pitch as the first fork.

- Next, we use an electric guitar and an amp to explain standing waves on a string. We can demonstrate the use and physics behind harmonics, and how they are used to accurately tune a guitar, or any instrument with strings. We can also use wave speed and frequency, and v = 2L/n * fn to determine fret length and spacing on guitars. Furthermore, we can display the same thing that the tuning forks showed earlier; that we can drive a string at a resonant frequency when another string is struck loudly, tuned to the same note.

- The phenomenon of beats is also demonstrated using a guitar. By tuning two strings to a note very close to eachother, we can hear beats by tuning one of them farther or closer to the other string.

- Lastly, we can drive the resonant frequency on a long, solid, aluminum bar. We need violin bow rosin, which is cheap and easy to find. The rosin is rubbed onto the bar, until there is a good resistance when the bar is rubbed. Then, while holding the bar between your thumb and first finger of one hand directly in the middle, one end is rubbed with the other hand, from the middle outward. If enough pressure is applied and the motion is uniform, there will be a large sound. This is the resonant frequency of the bar itself. This sound is the first normal mode of the bar. If it is held ¼ of the way from the end, the sound heard is the second mode.

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