Ch 17 notes

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Ch 17 notes

• WAVES

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What is a Wave?

• Waves-rhythmic disturbances that carry energy
  through matter or space
• Medium-material through which a wave can travel
  and transfer energy
• solid, liquid, gas, or combination

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Three main types

• Transverse Wave-medium move at right angle to
  direction of wave
• Longitudinal Waves-matter vibrates in the same
  direction as the wave travels, parallel
• Surface Wave-travels along a surface separating
  two media, most common are ocean waves

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Transverse Wave

• Wavelength Crest
• Amplitude
• _ _ _ _ _ _ _ _ _ _ _ _ _ _ _rest point
  (equilibrium) _ _
• Amplitude
• Trough

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Transverse Wave

• Crest-highest point of the wave above the rest
  point
• Trough-lowest point below the rest point
• Wavelength-distance between a point on one wave
  and the same point on the next cycle of the wave
• Amplitude-max displacement of the medium from its
  rest point, corresponds to the amt of energy a
  wave carries (more energy greater amplitude)

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Transverse Wave

• Frequency- of wavelengths that pass a fixed
  point each second, measured in Hertz (Hz)
  (Increasing Frequency wavelength decreases)
• Period-time it takes for one wavelength to pass a
  point (Increasing Frequency period decreases)

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Longitudinal Waves

• Longitudinal Waves-matter vibrates in the same
  direction as the wave travels, parallel

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Longitudinal Waves

• aka compressional waves
• compression-area where particles in a medium are
  spaced close together
• rarefaction-area where particles in a medium are
  spread out

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Surface Wave

• Surface Wave-travels along a surface separating
  two media, most common are ocean waves

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Wave speed

• Velocity wavelength x frequency
• V ? (lambda) x f
• m/s m x Hz

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Wave Speed

• One end of a rope is vibrated to produce a wave
  with a wavelength of 0.25meters. The frequency of
  a wave is 3 hertz. What is the speed of the wave?

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Wave Speed

• Wavelength 0.25m
• Frequency 3Hz
• Speed ?
• Speed Wavelength x Frequency
• Speed 0.25m x 3Hz
• Speed 0.75m/s

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Behavior of waves

• Reflection
• wave bounces off a surface that it cannot pass
  through
• does not change speed or frequency, but wave can
  be flipped upside down

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Reflection
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Mount Moran, one of the Grand Tetons, Wyoming
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Behavior of waves

• Refraction
• bending of a wave as it enters a new medium at an
  angle
• one side of the wave moves more slowly than the
  other side

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Refraction
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As an ocean wave approaches the shore at an
angle, the wave bends, or refracts, because one
side of each wave front slows down before the
other side does.
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Behavior of waves

• Diffraction
• bending of wave as it moves around an obstacle or
  passes through a narrow opening
• diffracts more of its wavelength is large
  compared to the size of an opening or obstacle

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Diffraction
Crepuscular rays, due to scattering
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Behavior of waves

• Interference
• occurs when two or more waves overlap and combine
  together
• Two types
• constructive-the waves add together
• destructive-the waves subtract from each other as
  they overlap

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Constructive
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Destructive
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Interference
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Node versus Antinode
Areas where destructive interference continually
occurs are called nodes. Areas where constructive
interference continually occurs are called
antinodes
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• Standing wave
• a wave that appears to stay in one placer it
  does not seem to move through the medium.
• It forms only if half a wavelength or a multiple
  of half a wavelength fits exactly into the length
  of a vibrating cord.

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Sound

• Speed of sound depends on
• type of medium-solid best conductor
• no sound on moon or in space (no medium)
• temperature of medium-faster at higher temps

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Sound

• Intensity rate at which a waves energy flows
  through a given area
• Loudness human perception, measured in decibels
  (dB)

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Sound

• Pitch highness or lowness of a sound
• high frequency high pitch
• low frequency low pitch
• human hear between 20 20,000 Hz
• Ultrasonic is above 20,000 Hz
• Infrasonic (subsonic) is below (thunder)

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Sound

• Resonance if the sound that reaches an object
  is at the same frequency of the object, the
  object will begin to vibrate at that frequency
• Noise pollution includes sounds that are loud,
  annoying or harmful to the ear

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Why do concert places usually have carpet on
walls and floors?
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Doppler effect

• A change in sound frequency caused by motion of
  the sound source, motion of the listener, or both
• Higher pitch, higher frequency as object
  approaches
• Lower pitch, lower frequency as sound source
  moves away

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