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Sound Waves

Sound Waves. What You Already Know. Principle of Linear Superposition When two or more waves are present simultaneously at the same place, the disturbance is the total of the from the individual waves. Constructive Interference

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Sound Waves

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  1. Sound Waves

  2. What You Already Know • Principle of Linear Superposition • When two or more waves are present simultaneously at the same place, the disturbance is the total of the from the individual waves. • Constructive Interference • When two wave sources vibrate in , a difference in path lengths that is zero or an integer # of leads to constructive interference. • Destructive Interference • When two wave sources vibrate in phase, a difference in path lengths that is or a half-integer # of leads to destructive interference.

  3. The Nature of Sound • Sound Waves • Created by a object such as the string on a violin, your vocal chords or the diaphragm of a loudspeaker. • Sound waves can be transmitted through , and . • If there is medium, there is ____ sound.

  4. www.library.thinkquest.org How is Sound Transmitted? • Sound is created by the collisions of and such that it is transmitted through the bulk matter.

  5. Sound Wave Characteristics • Condensation or Compression: Region of the wave where air is slightly . • Rarefaction: Region of the air wave where the is slightly . • Pure Tone: A sound wave with a single . • Pitch: An objective property of sound associated with . • frequency = pitch. • frequency = pitch. • Loudness: The attribute of sound that is associated with the of the wave. • Beat: When two sound waves overlap with a slightly different .

  6. vrms = Speed of Sound • Speed of sound depends on the through which it travels. kT m Where: k = Boltzman’s constant (1.38 x 10-23 J/K)  = Cp/Cv (~5/3 for ideal monotonic gases) T = Temperature (K) m = Average mass of air (~28.9 amu)

  7. v = B  Speed of Sound – An Alternative View • The speed of sound in other mediums may also be represented by a mathematical relationship that includes the density (ρ) and the bulk modulus (B) • Gases have a bulk modulus than liquids and liquids have a bulk modulus than solids. • Hence, as the bulk modulus , the velocity .

  8. Low Pitched Sound High Pitched Sound www.physicsclassroom.com Shift • The change in sound frequency due to the relative motion of either the source or the detector.

  9. Doppler Shift fd = fs(v + vd)/(v - vs) Where: • v = velocity of sound (343 m/s) • fd = frequency of the detector • vd = velocity of the detector • fs = frequency of the source • vs = velocity of the source • If the source is moving the detector, vs is . • If the source is moving from the detector, vs is .

  10. Waves in Musical Instruments • :Stringed instruments, such as the guitar, piano or violin, and horn and wind instruments such as the trumpet, oboe, flute and clarinet all form when a note is being played. • The standing waves are of either the type that are found on a string, or in an air column (open or closed). • These standing waves all occur at frequencies, also known as frequencies, associated with the instrument.

  11. Standing Wave Characteristics • While a standing wave does not itself, it is comprised of two waves traveling in directions. • : The series of frequencies where standing waves recur (1f, 2f, 3f,…). Where the first frequency is called the first (1f), the second frequency is called the second (2f), and so on. • The first harmonic = the first frequency (n = 1). • : The harmonic frequency + 1.

  12. www.cnx.rice.edu Harmonics and Overtones of Standing Waves

  13. www.electron4.phys.utk.edu www.cord.edu Standing Wave Characteristics (cont.) • The time for one wave to travel to the barrier and back is: ______ = ______ _____ = _____ • For a string fixed at both ends with n antinodes: fn = n(v/2L) n = 1, 2, 3, … • Each fnrepresents a or frequency of the string. • Since  = v/f, the relationship can be rewritten for  as follows. _____ = _____

  14. Longitudinal Standing Waves • instruments, such as the flute, oboe, clarinet, trumpet, etc. develop longitudinal standing waves. • They are a column of . • May be at one or both ends. • Wave will back regardless as to whether or not it is open or close ended.

  15. www.cnx.rice.edu Longitudinal Standing Waves – Tube • In an tube instrument like the flute, the harmonics follow the following relationship: fn = n(v/L) n = 1, 2, 3, …

  16. www.cnx.rice.edu Longitudinal Standing Waves –Tube on One End • In a tube instrument like the clarinet or oboe, the harmonics follow the following relationship: fn = n(v/L) n = 1, 3, 5, …

  17. Key Ideas • Sound waves are generated by a object such as the string on a violin, your vocal chords or the diaphragm of a loudspeaker. • Sound waves can be transmitted through , and . • If there is no , there is no . • Sound is generated by the cyclical of atoms and molecules. • and denote portions of the wave that are of slightly higher and lower pressure, respectively.

  18. Key Ideas • Sound waves travel at different in different mediums. • They up when going from air to a liquid to a solid. • tone is sound of a single frequency. • and are characteristics of sound that represent its frequency and amplitude, respectively. • When two sound waves overlap slightly due to mildly different frequencies, they generate a . • occur at multiples of the natural frequency.

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