Unit 8 Introduction to Vibrations & Waves · • Waves are a repeating pattern of motion: 1....
Transcript of Unit 8 Introduction to Vibrations & Waves · • Waves are a repeating pattern of motion: 1....
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Name: _____________________ Date: ________Period: ___________
Unit 8Introduction to Vibrations & Waves
Essential Questions:
• What are waves and what causes them?
• Why are waves important to study?
• How do we describe waves?
• How do we classify waves?
Vocabulary
• Waves
• Vibrations (or Oscillations)• Vibrations (or Oscillations)
• Medium
• Vacuum
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• Mechanical Waves
• Electromagnetic (EM) Waves
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Overview of Waves
Vibrating(or Oscillating)
ObjectWaves
…transfer energy or information as…
Frequency/PeriodSpeed, v
Wavelength, Amplitude
…described by these “properties” or “characteristics”…
e.g., Tuning fork
Mechanical Waves(move through matter
or a “medium”)
Longitudinal Waves Transverse Waves
Electromagnetic Waves(light waves, can move
through vacuum and matter)
1f
T
Frequency f or Period T
…described by…
…have a pattern of …
Only T
…have a pattern of …
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Atoms/molecules move perpendicular
to wave
Atoms/molecules move parallel to
the wave
Transverse Waves
Pattern of Electric and Magnetic Fields
Direction of energyDirection of energy
Wave Equations on MCAS Formula Sheet
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Waves
fc
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What is a wave?
• Waves are a repeating pattern of motion:1. Mechanical Waves occur in matter (or “in a medium”) –
repeating patterns of moving atoms/molecules
2. Electromagnetic or EM waves (light waves) are patterns of electric and magnetic fields, which do not need a medium to travel
• Waves carry energy and information from one place to another
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one place to another. We receive information primarily in the form of light or sound waves.
What causes waves?
• Waves are caused by something vibrating (or oscillating).
• Vibration (or oscillation) is a type of motion where an• Vibration (or oscillation) is a type of motion where an object moves and returns to the same position.
• Each back-and-forth motion is called a cycle.
Example of an
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Example of an electromagnetic wave:1) A charge (electron or proton) vibrates2) Vibration causes an electromagnetic wave
Example of sound wave in air:1) Speaker vibrates back-and-forth2) Vibration cause a pattern of compressions in air3) Energy travels to the ear as a sound wave in air
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Describing a wave pattern:Crest, Trough, Wavelength, Amplitude
Note: Frequency describes the vibrating source, and is the same for both source and wave
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Direction of wave velocity
Identify Transverse vs. Longitudinal Waves
• “Transverse” – across, perpendicular• Particles or fields move perpendicular to the direction of
the energy transfer, or wave velocity.
• “Longitudinal” – along, parallel• Particles or fields move parallel to the direction of energy
transfer, or wave velocity.
Slide 8Direction of wave velocity and energy
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Examples of mechanical waves in 1D- Wave energy travels in a straight line
Energy is transferred in the direction of wave velocity
Longitudinal and Transverse Waves in a Slinky
wave velocity.
Matter molecules do not travel with the wave.
“Longitudinal”Rope and slinky parts move parallel to the
Slide 9Direction of wave velocity and energy
move parallel to the direction of wave.
“Transverse”Rope and slinky parts move perpendicular to the direction of wave.
Sound waves are longitudinal waves in matter. Energy is transferred by colliding atoms.
M di ti lMedium particles do not move with the wave, but vibrate in place.
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Electromagnetic (EM) waves are transverse waves
• Light is energy is transferred as electromagnetic wave
• Shorter light wavelengths () have more energyg g ( ) gyLonger light wavelengths () have less energy
Higher Energy
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Radio Microwave Infrared Ultraviolet X-rays Gamma rays
Examples of mechanical waves in 2D- Wave energy travels along a surface
• Ripples on water surface
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• Sand patterns formed by vibrations on a flat metal plate“Cladni plate”
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Examples of waves in 3D- Wave energy travels in through 3D space
Light and sound sources create spherical waves traveling
through space in 3D
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Seismic waves caused by earthquakes are both transverse and longitudinal
S-WaveS-Wave
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Comparing Mechanical waves vs. EM waves
Similarities DifferencesBoth wave types:
Transmit energy and
Travels through a medium?• Mechanical waves travel
only through matter• Transmit energy and information
• Are described by frequency, speed, wavelength, and amplitude
only through matter, require a medium
• EM waves don’t need matter to travel – can travel through a vacuum, don’t require a medium
Wave Pattern?
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• Mechanical waves can be both transverse and longitudinal
• EM waves are transverse only