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Properties of sound

Properties of sound. Sound is a longitudinal wave Longitudinal waves travel at different speeds depending on the medium ( air @ 25 o C 346m/s, water 1490 m/s) Denser the medium, the faster it travels, energy can transfer faster through molecules closer together.

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Properties of sound

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  1. Properties of sound • Sound is a longitudinal wave • Longitudinal waves travel at different speeds depending on the medium (air @ 25oC 346m/s, water 1490 m/s) • Denser the medium, the faster it travels, energy can transfer faster through molecules closer together. • Loudness of a sound • depends on intensity (the amplitude of the wave. Higher amplitude … louder sound) • Measured in deciBels(dB), talking is about 50 dB over 120 dB is painful.

  2. Loudness/intensity

  3. Properties of sound • Pitch (high or low) is directly related to frequency. Higher frequency = higher pitch • (Also related to wavelength, indirectly. Bigger wavelength = lower pitch) • Humans hear between 20 Hz and 20,000 Hz. Below that range is infrasound, above is ultrasound.

  4. Musical Instruments • Rely on standing waves to make sound • Only certain wavelengths are made by instruments, depending on the size of the instrument • Fundamental frequency:the lowest frequency standing wave made by the instrument.

  5. Stringed Instruments • The wavelength of the fundamental frequency is twice the length of string. • Changing the size of the string changes the wavelength and the frequency. • Changing the tension on the string changes the medium (density) and the wave speed

  6. Wind/Brass Instruments • Change size of wave by opening closing holes, changes size of tube that standing wave is made in. • In an tube open at both ends, you get ½ the wavelength, so multiply by 2 to find the wavelength for the fundamental frequency • In a tube closed at one end, you get ¼ the wavelength, so multiply by 4 to find the wavelength for the fundamental frequency

  7. Musical Instruments • Strings make ½ wave, so mult. by 2. • Open tubes make ½ wave so mult. by 2 • Closed tubes make ¼ wave so mult. by 4.

  8. Resonance and Harmonics • Vibrations can cause other parts of the instrument and other objects to vibrate … called resonance. • The other standing waves created are called harmonics. • That’s why everyone’s voice sounds different and why instruments sound different when they play the same note. The have the same fundamental frequency (note), but different harmonics because of resonance • Waves interfere, called beats

  9. How we hear • Outer ear focuses waves, passes them to ear drum (middle ear) which passes them to three bones (hammer, anvil, stirrup) to the cochlea (inner ear) which resonates at certain frequencies. • Hair cells pick that up and transmit to brain.

  10. Ultrasound and Sonar • Use speed of sound in medium and time to figure out how far away something is (e.g. bottom of ocean floor) • Ultrasound...frequencies beyond our hearing used in medicine (babies).

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