Sound

Doppler Effect The change in frequency due to the motion of the sound source or the receiver of the sound. Named after Christian Doppler Greater speed of sound = greater Doppler Effect

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Shock Waves Produced by supersonic aircraft *Supersonic = faster than speed of sound Made from overlapping spheres that form a cone and travel until they hit the ground

Shock Wave When waves reach the listeners they hear a sonic boom Due to the waves reaching the listener all at the same time

Sound Produced by vibrations Under ordinary circumstances: frequency of = frequency of vibrating source sound waves

Sound Pitch How we describe the frequency (loudness) of a sound High Pitch = High Frequency Low Pitch = Low Frequency

Sound Young people can generally hear from 20 to 20,000 Hz The older you get the more your hearing range shrinks *Especially the higher frequency sounds

Sound Infrasonic *Frequency below 20 Hz Ultrasonic *Frequency above 20,000 Hz Humans cannot hear these

Sound Compressional Wave

Sound in Air When you clap your hands you produce a pulse of air that travels through the room.

Sound in Air Think of this pulse in terms of a window in an empty room. When open the door you produce a compression which travels through the empty room to the open window and pushes the curtain outward. The pulse of compressed air traveled through the room.

Sound in Air When you close the door this pushes air particles out of the room which makes for low pressure in the room. This will make the air outside of the room rush inside and push the curtain inside the room. Called a rarefaction

Media that Transmit Sound If you put your ear to the ground you will hear the hoofbeats of running horses through the ground sooner than you would through the air.

Media that Transmit Sound Same in water. You will hear something sooner underwater than in the air.

Media that Transmit Sound Sound will travel faster in solids than liquids and faster in liquids than gases

Media that Transmit Sound Sound will not travel through a vacuum (empty space). Sound will not travel through space.

Speed of Sound Depends on the elasticity (ability of something to return to its original shape) of the material FYI: Steel is consider elastic and putty inelastic *Sound travels fifteen times faster in steel than air

Loudness Physiological sensation sensed in the brain Human perception of sound intensity

Loudness Measured in decibels, dB After Alexander Graham Bell

Loudness Whisper = 20 dB Street Traffic = 70 dB Rock Music = 115 dB Threshold of pain (humans) = 120 dB Jet engine = 140 dB

Natural Frequency Objects vibrate at their own specific set of frequencies Together this produces the object’s unique sound.

Natural Frequency Depends on object’s elasticity and shape Also, this is the frequency that requires the least amount of energy to continue.

Resonance When the forced vibration on an object matches the object’s natural frequency Increases the amplitude

Resonance Examples: Opera singers breaking windows

Resonance In 1831 English infantry troops marching across a footbridge caused the bridge to collapse. Their footsteps continued to resonate through the bridge until it collapsed. In 1940 the Tacoma Narrows Bridge collapsed due to wind generated resonance.

Tacoma Narrows Bridge http://www.teachertube.com/viewVideo.php?video_id=97000

Beats Occurs when two tones of slightly different frequency are sounded together Periodic variation in the loudness of sound

Parts of Your Ear Outer Gathers sound waves Middle Amplifies the sound waves Inner Converts the sound waves into nerve impulses

Parts of Your Ear

Middle Ear What are the three tiny bones in your middle ear? Stirrup Anvil Hammer

Inner Ear Contains the cochlea: spiral-shaped structure that contains liquid and tiny hair cells The hair cells in the cochlea begin to vibrate and send nerve impulses through the auditory nerve to the brain.

Hear loss When the tiny hair cells are damaged or destroyed your hearing will become damaged. New research suggests that these hair cells may be able to repair themselves.

In conclusion, if a tree falls in the woods and there is no one around to hear it does it make a sound?