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Sound

Sound. Sound Waves. Sound waves are longitudinal waves. The source of a sound wave is a vibrating object. Only certain wavelengths of longitudinal waves in the air can be detected as sound. Sound Waves. Sound waves require matter in order to propagate. They cannot travel in a vacuum

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Sound

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  1. Sound

  2. Sound Waves • Sound waves are longitudinal waves. • The source of a sound wave is a vibrating object. • Only certain wavelengths of longitudinal waves in the air can be detected as sound.

  3. Sound Waves • Sound waves require matter in order to propagate. • They cannot travel in a vacuum • The speed of sound is different in different materials. • The speed of sound is also somewhat dependent on temperature.

  4. Speed of Sound • Air (room temp) – 343 m/s • Air (0° C) – 331 m/s • Helium – 1005 m/s • Water – 1440 m/s • Steel – about 5000 m/s • Concrete – about 3000 m/s

  5. Loudness • Loudness is related to intensity. • Loudness itself is not a measurable physical quantity. • It depends on the listener. • Intensity is measurable, however.

  6. Loudness • Sound intensity levels are usually given on a logarithmic scale. • The unit on this scale is the decibel (dB) • β = 10 log (I/I₀) • β = sound level (in dB) • I = sound intensity • I₀ = base sound level

  7. Loudness • The base sound level used (I₀) is usually what is know as the “threshold of hearing” • This is the minimum intensity that is audible to a good ear. • 1.0 x 10ֿ¹² W/m²

  8. Sound Intensities • Threshold of hearing – 0 dB • Whisper – 20 dB • Talk, at 50 cm – 65 dB • Busy street traffic – 70 dB • Loud rock concert – 120 dB • Jet plane at 30 m – 140 dB

  9. Pitch • Pitch is related to frequency of a sound wave. • A high pitch corresponds to a high frequency. • The audible range is the range of frequencies that a normal person can hear.

  10. Pitch • Frequencies between 20 Hz and 20,000 Hz are audible. • The threshold of hearing varies for different frequencies. • It is easiest to hear sounds between 2000 and 5000 Hz.

  11. Pitch • Frequencies too high to hear are ultrasonic. • Some animals can perceive sounds up to 100,000 Hz (bats) • Frequencies too low to hear are infrasonic.

  12. Beats

  13. Beats • Occurs due to interference between two sound waves that are close in frequency. • The sound level rises and falls as time passes. • This regular change in intensity is a beat.

  14. Doppler Effect • The Doppler Effect is the apparent change in frequency of a wave due to relative motion between the observer and the sound source. • Has many uses.

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