Sound

1
Sound
2
The Origin of Sound

• All sounds are produced by the vibrations of the
  material objects.
• Molecules MUST be present for there to be sound
• There is no sound in a vacuum b/c there are
  almost no molecules

3
A Sound Wave

• Sound waves are longitudinal waves.
• Parts of a sound wave
• Compression areas of high pressure
• Rarefaction areas of low pressure
• As a source vibrates in a periodic fashion, a
  series of compressions and rarefactions is
  produced
• For all wave motion, it is not the medium that
  travels across the room, but the energy that
  travels.

4
Pitch

• Pitch term that refers to how high or how low
  sound frequencies appear to be
• high frequency high pitch
• low frequency low pitch
• Ex Males have a lower pitch, females have a
  higher pitch
• A higher frequency results in a smaller
  wavelength of the sound wave
• Frequency and wavelength are inversely
  proportional

5
Check Your Understanding

• Which as a higher pitch, a 440 Hz tuning fork or
  a 330 Hz tuning fork?
• The 440 Hz tuning fork b/c it has a higher
  frequency
• Which has a larger wavelength?
• The 330 Hz tuning fork b/c it has a lower
  frequency.

6
Media that Transmit Sound

• Medium the surrounding environment
• Media is plural for medium
• A medium is whatever a wave is moving through
• Ex air in a classroom, water in the ocean
• Most sounds we hear are transmitted through the
  medium of air.
• Solids and liquids are generally good conductors
  of soundmuch better than air.

7

• The speed of sound varies in different media. In
  general, sound is transmitted faster in liquids
  than in gases, and still faster in solids.
• Remember that sound DOES NOT travel through a
  vacuum

8
The Speed of Sound

• Sound travels much slower than light.
• The speed of sound in dry air at 0C is 330 m/s.
• The speed of sound at room temperature is 340
  m/s. This is the accepted value of the speed of
  sound.
• The speed of sound depends on
• The type of medium (SgtLgtG)
• The temperature of the medium
• Elasticity of the medium

9
Check Your Understanding

• Will sound travel faster in steel or silly putty?
• It will travel faster in steel because steel is
  more elastic than silly putty.
• Will sound travel faster in outer space or in
  water?
• In water. As outer space is a vacuum, sound
  cannot travel without the use of molecule.

10
Energy thru different media

• Remember that waves move energy, not matter
• This is true for sound waves
• When a sound wave changes its speed going thru
  different media, it also changes its KE
• A sound wave loses KE in air compared to water
  b/c it slows down
• A sound wave gains KE in a solid compared to
  water b/c it speeds up

11

• Any KE change results in a change in another form
  of energy
• Remember conservation of energy
• Ex heat, PE
• If a sound wave looses KE, then some of that KE
  may be converted to heat

12
Check Your Understanding

• When will a sound wave have the most KE, in the
  ocean or in a steel bridge?
• In a steel bridge. It can travel the fastest in
  an elastic solid, so it will have the greatest KE
• When will a sound wave have no KE?
• In a vacuum, like in outer space, because there
  is no sound in space so there is no KE

13
Check Your Understanding

• Will sound have more KE in a warmer or cooler
  room?
• In a warmer room. Molecules move faster as the
  temperature increases, causing the sound to move
  faster, which leads to more KE.

14
Loudness

• Intensity the amount of energy transported
  through a given area per unit of time.
• Amplitude and intensity are directly
  proportional. The louder the sound, the larger
  the amplitude.
• SI unit decibels (dB)
• Ex Mr. Ellwood has a high intensity to his
  voice, Mr. Alexander has a low intensity to his
  voice.

15
Interference of Sound Waves

• Constructive Interference ? crests (compressions)
  overlap
• Bigger amplitude
• louder sound.
• Destructive Interference ? crests (compressions)
  overlap with troughs (rarefactions)
• Smaller amplitude
• Quieter sound

16
Check Your Understanding

• A megaphone will use what type of interference?
• Constructive interference b/c megaphones increase
  volume, which is an increase in amplitude
• What type of interference is used in ear phone
  air traffic controllers wear to cancel out all
  sound?
• Destructive interference b/c a decrease in volume
  to zero, which is a zero amplitude