Three Chapter 10

• Sound waves can cause objects to vibrate (resonate if the frequency of the sound matches the natural frequency of the object).

• Sound at A causes B to vibrate.
• These tuning forks are attached to a wooden box that is open at one end. They form closed air columns.
• Closed Air column – an air column that is closed at one end and open at the other.
• Standing waves can be set up in a closed air column. Sound from a source at the open end interferes with sound reflected off the closed end.
• For standing waves to occur, certain conditions must be met.
  • The closed end must be a node because the reflection point is like the fixed end of a rope.
  • The open end must be a loop because it does not reflect a wave, and therefore, cannot behave as a node.
  • Therefore, the length of the column must be

• l = the length of the air column, n = 1, 2, 3, …. and l = wavelength of the sound.
• Resonance can also occur in an open-air column.
• Open Air Column – An air column that is open at both ends.
  • Since the column is open at both ends, there must be a loop at both ends.
  • Therefore, the length must be

• Musical Note – Sound from a source that vibrates in a uniform manner.
  • Only one or more constant frequencies are present.
• Music – A combination of musical notes.
• Noise – A combination of sounds characterized by vibrations that are constantly changing in frequency.
• Consonance – Combination of musical notes of specific frequencies that are pleasing to the ear.
• Dissonance – Combination of musical notes of specific frequencies that are not pleasing to the ear.
• The frequencies given in a musical scale are chosen to produce the most consonance.
• Diatonic Major Scale – the eight note scale like C major.
• Middle C has a frequency = 256 Hz. Therefore, high C has a frequency = 512 Hz.
• The standardized musical pitch is A above middle C, which has a frequency of 440 Hz.
• When a tuning fork is placed on a table, the sound is amplified and enhanced because.
  • the table vibrates. (amplifies the sound).
  • the table adds overtones (enhances the sound).
• This also happens with most stringed instruments. For example, the violin has the fundamental set up on the string. Some overtones are also on the string. Vibrations are transferred via the bridge to the body and the air inside the violin. Most of the sound is from the body of the violin and the air inside.
• The quality is dependent upon
  • type of wood
  • structure of body
  • quality of varnish
  • glue
  • etc.
• Wind instruments use resonant air columns.
• The sound originates as
  • vibrating air over an opening
  • vibrating lips
  • vibrating reed

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November 18, 2013