Sound Waves

1
Sound Waves

• Longitudinal (Compression) Waves

2
Entry Task

• In your notes, answer the following questions.
• Do sound waves travel faster in solid, liquid or
  gas? Why?
• How are musical notes made with a wind
  instrument, like a clarinet?
• How does one string on a guitar make different
  musical notes?
• Using wave theory explain how making sound with a
  wind instrument is essentially the same as making
  sound with a string instrument.

3
Sound Waves

• Sound waves are caused by vibrations, and carry
  energy through a medium.
• The speed of sound in a particular medium depends
  on how well the particles can transmit the
  compressions and rarefactions of sound waves.

compression
rarefaction
4
Properties of Sound Waves

• Loudness is determined by intensity.
• Intensity depends on the amplitude of the sound
  wave as well as your distance from the source of
  the waves.
• The greater the intensity of a sound, the louder
  the sound will seem.

5
Sound Intensity and Decibels
6
Properties of Sound (continued)

• Pitch is determined by frequency.
• The pitch is a measure of how high or low a sound
  is perceived to be depending on the frequency of
  the sound wave.
• A high-pitched sound corresponds to a
  high-frequency, and a low-pitched sound
  corresponds to a low frequency.

7
The Doppler Effect

• Frequency changes when the source of waves is
  moving.
• The Doppler effect is an observed change in the
  frequency of a wave when the source or observer
  is moving. Doppler

8
Properties of Sound (continued)

• Humans hear sound waves in a limited frequency
  range.
• Any sound with a frequency below the range of
  human hearing is known as an infrasound.
• An infrasound is slow vibrations of frequencies
  lower than 20 Hz.
• Any sound with a frequency above human hearing
  range is known as an ultrasound.
• An ultrasound is any sound wave with frequencies
  higher than 20 000 Hz. audible sound

9
Standing Waves

• Musical instruments rely on standing waves.
• Standing waves can exist only at certain
  wavelengths on a string.
• The primary standing wave on a vibrating string
  has a wavelength that is twice the length of the
  string.
• The frequency of this wave is called the
  fundamental frequency. frequency

10
Harmonics and Resonance

• Harmonics give every instrument a unique sound.
• Certain whole-number multiples of the fundamental
  frequency are called harmonics.
• Every musical instrument has a characteristic
  sound quality resulting from the mixture of
  harmonics.
• Instruments use resonance to amplify sound.
• Resonance is a phenomenon that occurs when two
  objects naturally vibrate at the same frequency.
  resonance

11
Application of Resonance

• Sound is not the only type of wave that
  experiences resonance.
• In November of 1940, the original Tacoma Narrows
  Bridge collapsed due to its structure at the
  midspan resonating with 42mph wind.
• You Tube video of Narrows bridge collapse

12
Ultrasound and Sonar

• Ultrasound imaging is used in medicine.
• The echoes of very high frequency ultrasound
  waves, between 1 million and 15 million Hz, are
  used to produce computerized images called
  sonograms.
• Some ultrasound waves are reflected at
  boundaries.
• Some sound waves are reflected when they pass
  from one type of material into another.
• How much sound is reflected depends on the
  density of the materials at each boundary.

13
Ultrasound and Sonar (continued)

• Sonar, sound navigation and ranging, is a system
  that uses acoustic signals and echo returns to
  determine the location of objects or to
  communicate.
• Sonar is used for underwater location.
• A sonar system determines distance by measuring
  the time it takes for sound waves to be reflected
  back from a surface. sonar
• d vt
• d is distance
• v is the average speed of the sound waves in
  water
• t is time

14
Speed of Sound

• Were going to do a little experiment or two
  together to see if we can calculate the speed of
  sound. Listen carefully to the instructions.
• You will need the lab worksheet and materials.
• When you are not working on one of the lab
  activities, you should be working on this
  assignment
• p. 498 review 1-7, 9, 10 answer in complete
  sentences.