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21.1 Properties of Sound

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

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  1. 21.1 Properties of Sound pp. 454 - 458 Mr. Richter

  2. Agenda • Introduction to sound. • Notes: • Frequency and Pitch • Amplitude and Loudness • The Speed of Sound • The Doppler Effect • Tests and Labs Back

  3. Objectives: We Will Be Able To… • Explain how pitch, loudness and speed are related to waves. • Explain the Doppler Effect.

  4. Frequency and Pitch

  5. 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).

  6. 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

  7. Amplitude and Loudness

  8. 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).

  9. 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)

  10. The Speed of Sound

  11. 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.

  12. 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.

  13. The Doppler Effect

  14. The Doppler Effect • Relative motion creates a change in frequency.

  15. 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.

  16. Wrap-Up: Did we meet our objectives? • Explain how pitch, loudness and speed are related to waves. • Explain the Doppler Effect.

  17. Homework • p. 458 #1, 3, 5 • p. 474 Reviewing Concepts #1, 4

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