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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

Slide 2

• 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 …

Slide 3

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

Slide 4

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.

Slide 10

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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

Slide 13

Seismic waves caused by earthquakes are both transverse and longitudinal

S-WaveS-Wave

Slide 14

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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?

Slide 15

• Mechanical waves can be both transverse and longitudinal

• EM waves are transverse only