Sound resonance

To every system, if it is disturbed and let free to oscillate by itself, the system will oscillate at its natural frequency

e.g. pendulum

If a system is oscillating at its natural frequency, and energy is add to it at a frequency = natural frequency of the system

The system will absorb the energy at 100% efficiency

System will oscillate at increasing amplitude

What will happen then?

Sound + wine glass 1

Sound + wine glass 2

Tacoma Narrows Bridge Story

Can we “see” sound waves?

We can “see” sound waves by using a CRO

CRO = Cathode Ray Oscilloscope

Musical notes and noises (Page 282)

•The waveforms of notes are regular.

•The waveforms of noises are irregular.

Tuning fork Mouth organ Noise

•The higher the frequency, the higher the

pitch.

•The loudness of a musical note is related to

the amplitude and frequency. For two musical

notes of the same frequency, the one with a

larger amplitude is louder.

• Different musical notes played by different

instruments have different waveforms and

thus different qualities.

CRO traces (by oboe)

CRO traces (by French horn)

Oboe 雙簧管 French horn 法國

號

Page 283

Ex. P.288 (5)