Characteristic Frequencies and the Decay of Composite Sounds Chapter 4 Characteristic Frequencies and the Decay of Composite Sounds

Preliminary Hypothesis Perhaps the hammer induces several frequencies on the skillet, whereas the soft object gives only one or few.

Tuning Fork Strike near mid-point Strike at the end

Superposition

Superposition We step through the two waves horizontally, adding the vertical displacements at each horizontal step.

Harmonic Discriminator Mic Bandpass Filter Skillet Here we strike the skillet to produce impulsive sound, record the result with the mic, and select the frequencies we wish with the filter.

Waveform for the Skillet

Decaying Sound Frequency (F) Initial Amplitude (Amax) Halving Time (T½)

Decaying Sound Thumping the bottom of a plastic cup

VIBRATION OF A PENDULUM Example - Metronome What does the period (T) depend upon? Length of the pendulum (l). Acceleration due to gravity (g). Period does not depend upon the bob mass or amplitude.

Pendulum Uses Timing Oil prospecting Walking When oscillations are small, the motion is called simple harmonic motion (shm) and can be described by a simple sine curve.

Computer pendulum Experiment with the pendulum at this link Another type of Simple Harmonic system