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21.1 Properties of Sound. pp. 454 - 458 Mr. Richter. Agenda. Introduction to sound. Notes: Frequency and Pitch Amplitude and Loudness The Speed of Sound The Doppler Effect Tests and Labs Back. Objectives: We Will Be Able To…. Explain how pitch, loudness and speed are related to waves.

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21 1 properties of sound

21.1 Properties of Sound

pp. 454 - 458

Mr. Richter

agenda
Agenda
  • Introduction to sound.
  • Notes:
    • Frequency and Pitch
    • Amplitude and Loudness
    • The Speed of Sound
    • The Doppler Effect
  • Tests and Labs Back
objectives we will be able to
Objectives: We Will Be Able To…
  • Explain how pitch, loudness and speed are related to waves.
  • Explain the Doppler Effect.
frequency and pitch1
Frequency and Pitch
  • Humans interpret the frequency of sound waves as pitch – how high or low the sound is perceived to be.
    • High pitch = high frequency (soprano)
    • Low pitch = low frequency (bass)
  • Humans have been able to hear sound waves between frequencies of 20 Hz and 20,000 Hz.
  • Pitch is subjective, meaning it is only our perception of what is happening. Sound waves’ frequencies are objective (can be measured).
frequency and pitch inaudible waves
Frequency and Pitch: Inaudible Waves
  • As we age, humans can hear less of the range of frequencies.
  • Enjoy it while you can!
    • https://www.youtube.com/watch?v=9g0yThhJcxY
  • Ultrasonic waves (~ 10MHz) can be used to produce images of the insides of objects like:
    • wombs (ultrasounds!)
    • bridges and airplane wings
amplitude and loudness1
Amplitude and Loudness
  • Humans interpret the amplitudeof a sound wave as loudness (volume).
    • The greater the amplitude of a wave, the louder it sounds.
  • However, volume (human perception of amplitude) is not directly proportional to amplitude.
  • Humans measure volume on the decibel (dB) scale.
    • If the amplitudeis 10 times greater (multiplied by 10), the decibel level increases by 10 dB (10 is added).
amplitude and loudness2
Amplitude and Loudness
  • For example: an orchestra has 6 violins. If the conductor wants the violin section to be 10 dB louder, how many more violins should he hire?
  • 54 more (54 + 6 = 60. Ten times as many as the original)
the speed of sound1
The Speed of Sound
  • Sound is a mechanical wave.
  • Reminder: a mechanical wave is a wave that passes through a physical medium (material).
  • The speed of sound depends on what medium the sound is traveling through.
the speed of sound2
The Speed of Sound
  • Sound waves , and all mechanical waves, travel by collisions of molecules (more in 18.2-18.3).
  • In general, sound travels faster through solids than liquids, and more quickly through liquids than gases.
  • The more closely packed the molecules are, the more quickly collisions can happen.
the doppler effect1
The Doppler Effect
  • Relative motion creates a change in frequency.
the doppler effect2
The Doppler Effect
  • As an object moves toward an observer the sound waves arrive more frequently, resulting in a higher pitch.
  • The actual frequency of vibration of the object (car horn) does not change.
  • As the object moves away from the observer, the sound waves arrive less frequently. Lower pitch.
  • Note: the Doppler Effect only occurs with moving objects, not stationary objects closer or farther away.
wrap up did we meet our objectives
Wrap-Up: Did we meet our objectives?
  • Explain how pitch, loudness and speed are related to waves.
  • Explain the Doppler Effect.
homework
Homework
  • p. 458 #1, 3, 5
  • p. 474 Reviewing Concepts #1, 4