Sound

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Sound

  1. 1. is a disturbance that is transportedthrough a medium via the mechanismof particle-to- particle interaction.is a wave that is created by vibratingobjects and propagated through a mediumfrom one location to another. is a mechanical wave.
  2. 2. The vibrations of the object set particlesin the surrounding medium in vibrationmotion, thus transporting energy through the medium. For a sound wave travelingthrough air, the vibrations of the particlesare best described as longitudinal.
  3. 3. Compressions are regions of high air pressure. Rarefactions are regions of low air pressure. The diagram below depicts a sound wave created by a tuningfork and propagated through the air in an open tube.
  4. 4. 1. There is a medium that carries the disturbancefrom one location to another.2. There is an original source of the wave, somevibrating object capable of disturbing the firstparticle of the medium.3. The sound wave is transported from onelocation to another by means ofparticle-to-particle interaction.
  5. 5.  refers to “how often” the air particles vibrate.The sensation of a frequency is commonly referredto as the pitch of a sound.A high pitch sound corresponds to a high frequencysound wave and a low pitch sound correspondsto a low frequency sound wave.
  6. 6. Any sound with a frequency below the audiblerange of hearing(i.e., less than 20 Hz) is known as an infrasound and any sound with a frequency abovethe audible range of hearing (i.e., more than 20 000 Hz) is known as an ultrasound.Hearing Capacity Dogs ( 50 Hz – 45 000 Hz ) Cats ( 45 Hz – 85 000 Hz ) Bats ( > 120 000 Hz ) Dolphins ( > 200 000 Hz ) Elephant ( 5 Hz – 10 000 Hz ) Human ( 20 Hz – 20 000 Hz )
  7. 7. • The amount of energy that is transported past a given area of the medium per unit of time is known as the intensity of the sound wave.• The greater the amplitude of vibrations of the particles of the medium, the greater the rate at which energy is transported through it, and the more intense that the sound wave is.• Intensity is the energy/time/area; and since the energy/time ratio is equivalent to the quantity power, intensity is simply the power/area.• Typical units for expressing the intensity of a sound wave are Watts/meter2.
  8. 8. • The scale for measuring intensity is the decibelscale.• The faintest sound that a human ear can detect isknown as the threshold of hearing.• While the intensity of a sound is a very objectivequantity that can be measured with sensitiveinstrumentation, theloudness of a sound is more ofa subjective response that will vary with a numberof factors.• Despite the distinction between intensity andloudness, it is safe to state that the more intensesounds will be perceived to be the loudest sounds.
  9. 9. v = 331 m/s + (0.6 m/s/C)•T
  10. 10. Medium Speed of sound, (m/s)Air 330Seawater 1 540Freshwater 1 410Brass 3 650Copper 4 000Wood 4 650Steel 4 950Iron 5 000Aluminum 5 140Glass (soda) 5 150(Vacuum) -0-
  11. 11. 1. Reflection of Sound Reflection of sound waves off of surfaces can lead to one of two phenomena - an echo or a reverberation.  An echo is produced in an empty room. A reverberation often occurs in a small room with height, width, and length dimensions of approximately 17 meters or less.
  12. 12. 2. Refraction of Sound Sound waves are known to refract when traveling over water.
  13. 13. 3. Diffraction of Sound Waves  Sound waves moving around corners or edges.4. Interference of Sound Waves
  14. 14. 5. Beat refers to the rate at which the volume is heard to be oscillating from high to low volume.
  15. 15. can be described as the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for the observer and thesource are approaching and an apparent downwardshift in frequency when the observer and the sourceis receding.
  16. 16. Sample Problem: On a hot summer day, a peskylittle mosquito produced its warning soundnear your ear. The sound is produced by thebeating of its wings at a rate of about 600wing beats per second. a. What is the frequency in Hertz of thesound wave? b. Assuming the sound wave moveswith a velocity of 350 m/s, what is thewavelength of the wave?
  17. 17. Check Your Understanding Identify the following statements whether TRUE or FALSE. 1. A sound wave is a mechanical wave. 2. A sound wave is a means of transporting energy without transporting matter. 3. Sound can travel through a vacuum. 4. A sound wave is a transverse wave. 5. To hear the sound of a tuning fork, the tines of the fork must move air from the fork to ones ear.
  18. 18. 6. Intense sounds are usually perceived asloud sounds.7. The speed of a sound wave dependsupon its frequency and its wavelength.8. Sound waves would travel faster on awarm day than a cool day.9. A high pitched sound has a lowwavelength.10. Ultrasound waves are those sound waveswith frequencies less than 20 Hz.

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