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Waves and Oscillations

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3C 20.20 - Differential & Sympathetic Tuning Fork Set

Demonstrates: Beat phenomena and resonance.
Description: A set of two resonance tuning forks, one is adjustable for different pitch.

3C 20.40 - Boomwhacker Resonance

Demonstrates: One speaker is in a cap that completely closes the tube end, and the resonances are those of a half-open tube. (The acoustic impedance is high at these resonances.) A second speaker is in a cap with slots cut in it, and the resonances are those of the fully open tube. (The acoustic impedance is low at these resonances.)
Description: A small speaker & frequency generator drive resonances in a boomwhacker tube. Resonances can be heard (the sound is louder) and/or measured with a cellphone dB app.

3C 40.10 - Lecture Hall Acoustics

Demonstrates: Nodes.
Description: Two speakers emit a continuous tone. Students walk around until they find a node.

3C 50.10 - Introduction to Sound

Demonstrates: That different sounds have different wave patterns.
Description: The keyboard's signal is displayed on the large overhead screen using the Proxima projector and a computer input.

3C 50.20 - Sound Meters

Demonstrates: Sound levels in decibels.
Description: A hand held meter.

3C 70.10 - Pith Ball Resonance

Demonstrates: Resonance using sound waves.
Description: Sound waves from one tuning fork induce motion in a second tuning fork. This causes a pith ball resting on the second fork to be knocked away.

3C 70.20 - Crystal Singing Bowl

Demonstrates: Sound waves, and pure notes vs harmonics
Description: The bowl makes different tones when it is lightly tapped vs. "bowed" with the suede wand. The free spectrum analysis software Audacity can be used to show students the spectrum of tapped and bowed notes. The tapped bowl has several prominent anharmonic overtones (just like a bell.) However, the bowed bowl creates a steady, repetitive tone ... and thus, from Fourier series, all the overtones must be (and are) perfectly harmonic. In addition, the bowed bowl may have overtones that are not present in the tapped bowl (for example, a 2nd harmonic). Since the tapped bowl excites essentially all the low lying normal modes, this second harmonic is actually not a normal mode, but simply the result of a high amplitude vibration of the fundamental mode, driving it into nonlinearity. (This discussion might be more suitable for upper division classes!)