Sound Waves

Sound is a Longitudinal Wave

• particles vibrate parallel to the direction of the motion of the wave

Terminology

• Compressions: areas where particles come closer together• Rarefactions: regions where

particles are further aparthttp://surendranath.tripod.com/Applets/Waves/LWave01/LW01.html

• Vibrations are the source of all sound, whether they are visible or invisible• Visible vibrations–Speaker, guitar strings, etc

• Invisible vibrations–Air molecules (blowing over bottle),

tuning fork, etc.

• Tuning Fork/Strobe Light Demo• When a tuning fork vibrates, the tines move in

and out creating longitudinal waves in air• Sound depends on the quality of vibration

How your ear works

How your ear works• If a compression hits your ear drum, –The pressure from outside your ear drum

pushes your ear inwards• If a rarefaction hits your ear drum–Pressure from inside your ear pushes

your ear drum outwardsAs your ear drum moves in and out, your

brain interprets the movement as sound

Sound and your Ear

Range of Human Hearing

• Humans can typically hear an audible range of sound for 20 Hz and 20,000 Hz

• This breaks down as:– You get older– You listen to really loud music (concerts, etc)

Frequencies greater than 20kHz are ultrasonicFrequencies less than 20 Hz are infrasonic

The Human Ear

Let’s test your hearing

Sound Technologies• Sonar– Uses sound to detect things underwater– Process called echolocation – by analyzing echoes

(reflected sound) we can detect objects

• Echolocation– Bats and dolphins use echolocation to find prey

and locate things around themselves

Sound Needs a Medium!

• Sound always needs a medium to travel through (in space, no one can hear you scream)

• Medium can be air, water (hear a boat approaching underwater), steel (put your ear to a train track), etc.

• The more densely packed the medium, the faster the speed of sound

• The larger the amplitude of the sound wave, the louder the sound

Pitch• the human perception of the highness or

lowness of sound• depends on the frequency of sound• Big distinction between pitch and frequency is

that above 20,000 Hz the pitch of the sound doesn’t exist because the human ear can’t detect it

Questions

1) Provide a brief description of how sound travels through the air and interacts with your ear. Use the terms: longitudinal, compression, refraction, ear drum and medium.

2) Describe the pitch of the sound that you would hear at 30Hz and 19000 hz.

3) If you were placed in a vacuum with a friend. He starts screaming at a constant volume and frequency. As the air was removed from the vacuum, how would the sound you hear change? Explain.

4) In space there is no air so astronauts use radio waves to communicated with each other. If the radio breaks, what could astronauts do to communicate with sound?