Sound Waves

1
Sound Waves

• How We Hear
• Properties of Sound
• Using Sound

2
Bell Work 10-13-09

• What type of wave has crests and troughs?
  Describe the difference between a crest and a
  trough.
• Crest - highest point of a transverse wave
• Trough - lowest point of a transverse wave
• What type of wave has compressions? What happens
  to molecules during a compression?
• Compression - the molecules in the longitudinal
  wave are compressed together
• What type of wave has rarefactions? What happens
  to the molecules during a rarefaction?
• In a rarefaction, the molecules in the
  longitudinal wave become spread apart.

3
Mythbusters VideoBreaking Glass

• In this video, Adam and Jaime try to test the
  myth that a singer can break glass using only
  their voice.

4

• As the frequency of a sound wave increases
• Pitch increases.
• Pitch decreases.
• Pitch stays the same.
• HELP! I dont get it!

5
Differences in Waves

• This ear-shaped boat moves up and down as the
  waves arriveas your eardrum does!
• Which waves are soft? Loud?
• Which waves are low? High?

6
A
B
highest amplitude
highest amplitude
loudest
loudest
lowest frequency
highest frequency
lowest pitch
highest pitch
D
C
lowest amplitude
loudest
highest amplitude
softest (quietest)

• Which sound wave(s) has the
• lowest amplitude?
• highest amplitude?
• lowest frequency?
• highest frequency?
• lowest pitch?
• highest pitch?
• softest (quietest)?
• loudest?

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Speed of Sound

• The speed of sound depends on the properties of
  the medium through which it is traveling

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• Elasticity is the ability of a material to bounce
  back after being disturbed.
• More elastic faster
• Solid most elastic
• Liquid not very elastic
• Gas inelastic
• Density is the amount of matter in a given
  volume.
• More density particles closer faster
• Temperature is a measure of the average kinetic
  energy.
• Higher temperature faster
• Lower temperature slower

9
Graph the following data
Show how the speed of sound through air changes
with temperature. Show temperature from -20C
to 30C on the horizontal axis. Plot speed from
300 m/s to 400 m/s on the vertical axis.
Should you choose a line graph or a bar graph for
this data?
10
Breaking the Sound Barrier

• When an object passes through the air, it creates
  a series of pressure waves in front of it and
  behind it.
• These waves travel at the speed of sound,
• As the speed of the object increases, the waves
  are forced together, or compressed, because they
  cannot "get out of the way" of each other.
• When the object reaches the speed of sound, the
  waves merge into a single shock wave.
• This critical speed is known as Mach 1761 mph!!

Rapid condensation of water vapor due to a sonic
shock produced at sub-sonic speed creates a vapor
cone
11

• The cracking sound a bullwhip makes when properly
  wielded is, in fact, a small sonic boom. The end
  of the whip, known as the "popper", moves faster
  than the speed of sound, thus resulting in the
  sonic boom.4 The whip is quite possibly the
  first human invention to break the sound barrier.

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Moving Faster than Sound

• Oct. 14, 1947, Chuck Yeager became the first
  person to fly faster than the speed of sound. He
  flew at a high altitude in order to do this.
  Why?
• At higher altitudes the air is colder, so sound
  travels more slowly.
• So, to break the sound barrier at a high
  altitude, he did not have to fly as fast as he
  would have at a lower altitude.
• LOWER TEMPERATURE
• SLOWER TRANSFER OF ENERGY
• LOWER SPEED OF SOUND

• Oct. 15, 1997, Andy Green became the first person
  to drive a land vehicle faster than the speed of
  sound. Why did he choose to drive in the desert?
• Cooler at night and in the morning
• Flat
• Large open spaces

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Match the Sound Waves
1.
A

• Which size instrument will make a high sound? A
  low sound?
• Which waves show a high sound?
• Which waves show a louder sound? A quieter one?
• Match the instrument or group of instruments to
  the correct sound wave.

2.
B
3.
C
4.
D
5.
E
F
6.
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Reflection of Sound Waves

• Echo- A reflected sound wave
• Smooth hard surfaces reflect best
• Rough soft surfaces reflect poorly
• Energy not reflected is absorbed or transmitted
  through the material

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Echolocation

• Echo- a reflected sound wave
• Echolocation- using the reflection of sound waves
  (echo) to navigate, locate prey, and to determine
  the direction and distance of objects
• Used by bats, dolphins, whales
• Can humans use echolocation?
• Use ears to interpret echoes (to estimate
  size/shape of room)
• Ben Underwood!

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• http//player.discoveryeducation.com/index.cfm?gui
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  romSearch1productcodeUS

17
Extra Credit

• Draw a house and write down the measurements you
  used in centimeters AND millimeters.

• It MUST have a door and two windows.
• It MUST have a triangle roof.
• It must be colored and have grass and trees!