SoundCh. 26.1-26.3

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Review

• What’s a wave? What does it transport?

• Wave is a disturbance traveling through a medium transporting energy from one location to another.

• Remember the slinky? How is its wave similar to sound waves? Any guesses?

Listen . . .

• Listen, quietly, for a few minutes, writing down the name of each sound you hear, and where it is coming from

• Sound is the only thing that our ears can hear. The source of sound or any wave motion is a vibrating object

Quick Demo

1. Strike the prongs of a tuning fork with a pencil and then hold the fork close to your ear.  What happens?  Touch the prongs of the fork.  What happens?

2. Strike the prongs of the tuning fork and place the ends of the prongs in a glass of water.  What happens?

Objectives

1. Relate the pitch of sound to its frequency 2. Describe the movement of sound through

air3. Describe how bats and dolphins use sound4. Compare the transmission of sound

through air with that through solids, liquids, and a vacuum

Origin of Sound• All sound produced by vibrating source

– Strings on a guitar --> sound board (demo?) – Reed in a saxophone -->air column in sax

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Quick Physiology Lesson

• Creating Sound:– Put your hand on your

throat when you talk• Windpipe blows air

across your chords in your throat causing them to vibrate and make a sound

• Rubber band and cup demo

• Listening . . .

Determining Pitch

• Let’s review frequency. What is it?

• Frequency: # of vibrations per second Hz)

• Pitch of a note determined by frequency– High frequency --> high

pitch

• Wind instruments have a long, thin column of air

• Sound wave travels down tube, reflects off of the top and bottom, until it can escape

• Longer the tube, lower the f, lower the pitch

• Shorter the tube, higher the f, higher the pitch

• Opening/closing holes changes tube length which changes pitch

• Demo with recorder

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Pitch of Wind Instrument

Remember…

• Sound waves are mechanical waves– require a medium in order to

transport their energy

• What’s the medium used to get this sound to your ears?

What pitches can we hear?

• 20 to 20,000 Hz

• Sound waves – below 20Hz

• Infrasonic– above 20,000Hz

• Ultrasonic

Elephants and Bats

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Dolphins• Send sound to the sea

floor --> creates image• Send sound to other

dolphin --> put image in their head

• Receive and send info with the same “sense.”

• Do humans?

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Checkpoint

1. The higher the frequency of a wave, the _________ the pitch.

• higher

2. Which chamber in a trumpet would produce a lower frequency: a short chamber or a long chamber? Why?

Longer chamber --> longer wavelength --> lower frequency

Compressed Air

• Vibrations produce pulses of compressed air, remember?

• Do sound waves move like the slinky or the spring? (show both) What type of waves are sound waves?

• Longitudinal!

Compressions vs. Rarefactions• These pulses push into their

neighbors, who push their neighbors, etc.

• Compressions: – pulse of compressed air

• i.e., door/curtain

• Rarefaction: – a disturbance in air when pressure

is lowered

• Candle Demo

Sound needs a medium

What are the best conductors of sound?

• Put these in order: liquid, air, solid.• Why is one a better conductor than

the other?– Depends on object’s elasticity--more on

this next lecture

• Can you hear voices in outer space?• Tin can activity