Waves

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Waves
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The Nature of Waves
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What is in a wave?

• A wave is a repeating disturbance or movement
  that transfers energy through matter or space.
• For example, during earthquakes, energy is
  transferred in powerful waves that travel through
  Earth.

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Wave and Energy

• A pebble falls into a pool of water and ripples
  form.
• Because it is moving, the falling pebble has
  energy.

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• As it splashes into the pool, the pebble
  transfers some of its energy to nearby water
  molecules, causing them to move.
• What you see is energy traveling in the form of a
  wave on the surface of the water.
• Raft

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• The waves dont even carry the water along with
  them.
• Only the energy carried by the waves moves
  forward.
• All waves have this property
• They carry energy without transporting matter
  from place to place.

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Making Waves

• A wave will travel only as long as it has energy
  to carry.
• Anything moving up and down or back and forth in
  rhythm is vibrating.
• All waves are produced by vibrating matter

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Mechanical Waves

• Some wave require matter to transfer the energy.
• The matter the waves travel through is called a
  medium.
• The medium can be a solid, a liquid, a gas, or a
  combination of these.

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• The two types of mechanical waves are transverse
  waves and compressional waves.

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Transverse Wave

• In a transverse wave, matter in the medium moves
  back and forth at right angles to the direction
  that the wave travels.
• For example, a water wave travels horizontally as
  the water moves vertically up and down.

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Compressional Waves

• In a compressional wave, matter in the medium
  moves back and forth along the same direction
  that the wave travels.
• The wave carries energy, but not matter, forward
  along the spring.

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• Compressional waves also are called longitudinal
  waves

• Sound creates compressional waves.

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Deep Water Waves

• A water wave causes water to move back and forth,
  as well as up and down.
• This motion causes both transverse and
  compressional waves

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Seismic Waves

• Forces in Earths crust can cause regions of the
  crust to shift, bend, or even break.

• The breaking crust vibrates, creating seismic
  waves that carry energy outward.

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• Seismic waves are a combination of compressional
  and transverse waves.
• They can travel through Earth and along Earths
  surface.

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Wave Properties
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The Parts of a Wave

• Transverse waves and compressional waves have
  different characteristics crests and trough,
  compressions and rarefactions.
• They also have similar properties wavelength,
  frequency, period, amplitude, and wave speed.

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The Parts of a Transverse Wave

• A transverse wave has alternating high points,
  crests, and low points, troughs.

Rest position is also called equilibrium.
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Wavelength of Transverse Wave

• A wavelength, ?, is the distance between one
  point on a wave and the nearest point just like
  it.

• Wavelength is the distance from crest to crest or
  trough to trough.

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The Parts of a Compressional Wave

• A compressional wave has regions where the
  particles are close together, compressions.

• And regions where the particles are further
  apart, rarefactions.

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The wavelength of a Compressional Wave

• A wavelength is the distance between two
  neighboring compressions or two neighboring
  rarefactions.

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Amplitude

• Amplitude is related to the energy carried by a
  wave.
• The greater the waves amplitude is, the more
  energy the wave carries.

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Amplitude of a Transverse Wave

• The amplitude is the distance from the crest or
  trough of the wave to the rest position of the
  medium.

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The Amplitude of a Compressional Wave

• The amplitude of a compressional wave is related
  to how tightly the medium is pushed together at
  the compressions.
• The denser the medium is at the compressions, the
  larger its amplitude is and the more energy the
  wave carries.

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Frequency, f

• The number of wavelengths that pass a fixed point
  each second.
• The rate of vibration
• Find the frequency of a transverse wave by
  counting the number of crests or troughs that
  pass by a point each second.
• Expressed in Hertz (Hz).

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Period, T

• The amount of time it takes one wavelength to
  pass a point.
• As the frequency of a wave increases, the period
  decreases.
• Units of seconds, s.

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Frequency Period

• The frequency, f, and period, T, are reciprocals
  of each other.

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Speed of a Wave

• The speed of a wave depends on the medium it is
  traveling through.
• Sound travels faster in solids than gases.
• Light travels faster in air than water.

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Calculating the Speed of a Wave

• vfl
• Where
• v is speed in m/s
• f is frequency in Hz
• l is wavelength in m