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Sound

Sound. Advanced Physical Science 2012 Lockwood. Sound Waves. Sound waves are LONGITUDINAL waves Also called COMPRESSION waves and… have compressions and rarefactions (vs. Transverse waves that have crests and troughs) are mechanical waves (mechanical waves require a medium).

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Sound

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  1. Sound Advanced Physical Science 2012 Lockwood

  2. Sound Waves • Sound waves are LONGITUDINAL waves • Also called COMPRESSION waves and… • have compressions and rarefactions (vs. Transverse waves that have crests and troughs) • are mechanical waves (mechanical waves require a medium)

  3. How Sound Works • Sound needs a medium to travel (a medium is a solid, liquid or gas) • You can’t hear an explosion in space (no particles= no sound!) • Energy is transferred from particle to particle through matter. • The speed of sound depends on the medium and the temperature • Sound travels faster in liquid than a gas and fastest in solids (more particles) • Sound in any medium slows if the temperature is lowered (particles move more slowly at lower temps, energy is transferred more slowly)

  4. How we hear • Outer ear collects sound • Middle Ear amplifies • Inner ear converts

  5. Properties of Sound • Intensity and loudness • Intensity depends on the energy in a sound wave. • Loudness is… • human perception of intensity. • measured in decibels. • Subjective! (This means it depends on the person who is hearing it.) • a personal, physical response to the intensity of sound. • As intensity increases, so does loudness, but loudness also depends on the listener’s ears and brain.

  6. Frequency & Pitch • Frequency of the sound wave depends on how fast the source of the sound is vibrating • High Frequency means more vibrations hitting the ear • How an osciliscope “sees” a sound wave… Low Frequency High Frequency Remember…sound waves are NOT transverse waves as shown by the osciliscope!

  7. Pitch • Pitch is how we hear frequency of sound waves • Pitch depends on frequency High Frequency = High Pitched Low Frequency = Low Pitched • Pitch also depends on age and health-there are sounds that older people can not hear. • Healthy humans can hear from 20 hz to 20,000 hz • We are most sensitive from 440hz to 7000hz Click on the tuning fork to hear pitches at different frequencies:

  8. Ultrasonic vs. Infrasonic • Ultrasonic sound has a frequency GREATER than 20,000 Hz • Dogs: Up to 35,000 Hz • Bats: Over 100,000 Hz • Medical Diagnosis • Infrasonic sound has a frequency BELOW 20 Hz • Felt rather than heard (earthquakes, heavy machinery)

  9. Resonance • Resonance – when the frequency of sound matches the natural frequency of an object • Tacoma Narrows Bridge Collapse (click for wikipedia information about collapse) • Example of RESONANCE • Click on the picture to view an old newsreel with video clip of the event.

  10. Standing Wave • “A wave that forms a stationary pattern in which portions of the wave are at rest position due to total destructive interference and other portions have large amplitude due to constructive interference” In other words…the wave seems like it’s “standing” rather than moving on one direction. • Click here for Standing Wave 1 • Click here for Standing Wave 2

  11. Doppler Effect • Change in frequency of a wave due to relative motion between source and observer. • A sound wave frequency change is noticed as a change in pitch. • Objects moving toward you cause a higher pitched sound. • Objects moving away cause sound of lower pitch. • Used in radar by police and meteorologists and in astronomy. • Click on the picture to hear an example of the Doppler effect.

  12. Music • Noise has no pattern • Music has a pattern and deliberate pitches. • Sound quality describes differences of sounds that have the same pitch and loudness. • Every instrument has its own set of overtones. • Musical instruments change their pitch by changing the frequency of the waves they produce • Loudness – increases with energy added to wave – amplitude • Timbre (pronounced tam – ber) -- Sound quality • This is what gives instruments their characteristic sounds

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