WAVES

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WAVES
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What is a wave?

• Weve all seen waves in a lake or ocean before,
  but these are just one type of wave. A wave can
  be defined as
• A disturbance traveling through a medium by
  which energy is transferred from one particle of
  the medium to another without causing any
  permanent displacement of the medium itself.

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Key points about waves

• Energy is what is moving along the wave.
• Matter is not being transported along the wave,
  just energy.
• There are many kinds of waves depending on the
  medium and the motion of the wave.

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Important Terms

• Medium the matter through which the wave is
  traveling.
• Propagation The continuation of a wave
  throughout a medium.
• Pulse An individual disturbance created in the
  medium. (Part of a wave)

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Types of waves

• All waves can be classified as one of two types
  depending on whether or not the wave requires a
  medium to travel through.

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Types of waves

• Mechanical Waves Require a medium to
  propagate.
• (examples water waves, sound, vibrations on a
  string, earthquakes).

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Types of waves

• Electromagnetic Waves- Do NOT require a medium.
  Can travel through a vacuum.
• (examples visible light, microwaves, radio,
  ultraviolet, infrared, x-rays)

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Types of waves

• Waves can also be classified based on the
  motion of the medium that the wave is traveling
  through.

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Transverse Waves

• Matter is displaced perpendicularly to the motion
  of the wave.

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Transverse Waves

• Notice that the particles of this material are
  all moving up and down while the wave is moving
  horizontally.

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Transverse Waves
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Transverse Waves

• Crest Highest displacement of a wave.
• Trough Lowest displacement of a wave.

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Transverse Waves

• Amplitude (A) The displacement of a wave at its
  crest or trough.
• The greater the amplitude, the greater the energy
  of the wave.

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Transverse Waves
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Transverse Waves

• Wavelength (?) the distance from one crest to
  the next crest, or one trough to the next trough.

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Wave Measurements

• Frequency (f) How many waves go by a certain
  point each second. In other words, how
  frequently a wave goes by.
• Frequency is measured in cycles per second
  otherwise known as Hertz (Hz).
• 1 cycle/s 1 s-1 1 Hertz 1 Hz

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Wave speed animation
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Wave Measurements

• Notice that as the frequency increases, so does
  the velocity of the wave.
• The Velocity (V) of the wave is directly
  proportional to both the wavelength and the
  frequency.
• V f ?
• Since the units are m s-1, the unit of velocity
  is m/s.

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Wave Measurements

• Since frequency is how many waves per second, the
  opposite measurement must be how many seconds per
  wave. This is called the Period (T).
• T 1 / f f 1 / T
• Since the Period is a measure of time, the unit
  is in seconds (s).

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Wave Measurements

• Velocity can be now expressed as

V ?
f
1 / T
/ T
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Longitudinal Waves

• Longitudinal waves are similar to transverse
  waves, except the oscillations of the medium are
  parallel to the motion of the wave, not
  perpendicular.

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Longitudinal Waves

• Compression Area where the matter is
  compressed together. (Analogous to a wave crest)

Rarefaction Area where the matter is pulled
apart. (Analogous to the wave trough)
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Longitudinal Waves
Focus on just one dot and follow it. What do you
notice?

• The red line represents the disturbance that is
  creating the waves.

The particles appear to be traveling all the way
across the screen, but look closer.
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Measuring Longitudinal Waves

• Wavelength The distance between two consecutive
  compressions or two consecutive rarefactions.

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Surface Waves

• Surface waves are unique from transverse and
  longitudinal waves because they only exist on the
  surfaces of the medium they are moving through.
• Examples water waves, earthquakes

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Surface Waves

• The motion of surface waves is a combination of
  transverse and longitudinal characteristics.

Focus on the movement of the two blue dots. In
what direction are they moving? How is their
motion different?
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Assignment

• Read pg. 381-384
• Do Problems 15-21 on Pg. 386