# The Nature of Sound Students will describe how sound is caused by vibrations, how it is transmitted through a medium. Students will also compare the speed.

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The Nature of Sound Students will describe how sound is caused by vibrations, how it is transmitted through a medium. Students will also compare the speed of sound in different media, explore the doppler effect, and explain how echoes are produced. Students will discuss the range of hearing for humans, and the threshold of pain.

Sound is caused by vibrations The medium is vibrating and particles are compressed and decompressed.

Another view of the particles vibrating back and forth

A cross section of a sound wave

Tuning Fork – notice how the sound spreads out in all directions. You can also see the reflection of some of the sound waves, as well.

Tuning Fork Sound Waves Time-lapse showing the compressions moving through the medium First second Second 2 Third second Fourth second Fifth second Sixth second Seventh second

Sound Spreads Out in All Directions Can you name the compressions and the rarefactions?

Amplitude of Sounds Both waves have the same frequency, but the top one has a much greater amplitude. This means that they have the same pitch (or “note” on a musical scale), but the top one is louder than the bottom one.

Sound vs Light Light travels at 3x10 8 m/s, whereas sound only travels at about 340 m/s That is 880,000 times faster!!!! So the music you hear out of your radio was transmitted through the air from radio towers as a form of light (radio waves) not sound waves 3x10 8 = 300000000

The speed of sound MediumSpeed of sound Air343 m/s Helium1005 m/s Water1482 m/s Sea water1522 m/s Wood (oak)3850 m/s Glass4540 m/s Steel5200 m/s

Also…the speed of sound depends on temperature! The cooler the media, the slower the speed of sound. Remember, the particles are moving slower when it is cooler, so they also transfer sound energy at a slower rate!

How much can the teacher really hear in class??? The average human can detect frequencies of 20 Hz to 20,000 Hz. (Augustyn can detect 2 Hz to 200,000,000 Hz) Sounds that are lower than 20 Hz are called infrasonic Sounds that are higher than 20,000 Hz are called ultrasonic Gum being chewed is about 5 Hz

Doppler Effect The Doppler Effect (for sound waves) is the apparent change in pitch as a sound approaches and then passes by Example: Train whistles at you while your standing by the tracks – it seems to be higher in pitch as it approaches, and lower after it passes by. The frequency (pitch) does not really change, it only appears to change.

Loudness is related to Amplitude The higher the amplitude, the louder the sound Loudness of sound is measured in decibels (db) Near total silence - 0 dB A whisper - 15 dB Normal conversation - 60 dB A lawnmower – 80-90 dB A car horn – 110-115 dB A rock concert or a jet engine - 120 dB Threshold of pain - 120 dB A gunshot or firecracker - 140 dB Jet engine 15 miles away – 140 dB Instant perforation of the ear drum – 160 dB

Echoes Echoes Echoes Sound waves bouncing off a surface. Best when sound bounces off smooth surfaces. Which provides a better echo? An empty house, or a house full of furniture and carpeting?

Students will describe how sound is caused by vibrations, how it is transmitted through a medium. Students will also compare the speed of sound in different media, explore the doppler effect, and explain how echoes are produced. Students will discuss the range of hearing for humans, and the threshold of pain.

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