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Today 2/24/14

• Read Chapter 13.7 to 13.9 (p455 to 461)

• Watch the rest of this presentation

• Complete example problems in the book• Complete HW

– Given at the end of the presentation

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Raymond A. Serway

Chris Vuille

Chapter ThirteenVibrations and Waves

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Wave Motion

• A wave = the motion of a disturbance

• Mechanical waves require – Source of disturbance

– A medium that can be disturbed – Some physical connection within the medium which allows

influence to the rest of the medium

• All waves carry energy and momentum

Section 13.7

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Types of Waves – Traveling Waves

• Flip one end of a long rope thatis under tension and fixed at theother end

• The pulse travels to the rightwith a definite speed• A disturbance of this type is

called a traveling wave

Section 13.7

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Types of Waves – Transverse

• Transverse wave = each element disturbed moves in adirection perpendicular to the wave motion

Section 13.7

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Video of Transverse Wave

• https://www.youtube.com/watch?v=AtlxBODxWHc

• https://www.youtube.com/watch?v=Rbuhdo0AZDU

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Types of Waves – Longitudinal

• Longitudinal wave = elements of the medium aredisplaced parallel to the motion of the wave

• Also called a compression wave

Section 13.7

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Videos of Longitudinal Wave

• https://www.youtube.com/watch?v=ubRlaCCQfDk

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Waveform – A Picture of a Wave

• The brown curve is a“snapshot” of the wave atsome instant in time

• The blue curve is the samewave at a later time

• The high points are crests

• The low points are troughs

Section 13.7

Crest

Trough

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Longitudinal Wave Represented as a Sine Curve

• A longitudinal wave can also be represented as a sine curve• Compressions of coils correspond to crests

• Stretches areas of coil correspond to troughs• Also called density waves or pressure waves

Section 13.7

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Producing Waves

Section 13.8

• The blade vibrates causingoscillates in simple harmonicmotion in the string

• A steady stream of pulses on avery long string produces acontinuous wave

• Each small segment of the string,

such as P, oscillates with simpleharmonic motion

Blade

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Amplitude and Wavelength

• Amplitude = maximumdisplacement of string abovethe equilibrium position

• Wavelength (λ) = distancebetween two successivepoints that behave identically

• Period (T) = time it takes tomove through one cycle

• Frequency (ƒ) = vibrations perunit time (ƒ=1/T)

Section 13.8

Δy = amplitude Δx = wavelength

Equilibrium (X=0)

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Speed of a Wave on a String

• The speed on a wave stretched under sometension, F

– v = velocity (speed) – F = force (tension in the string)

– m is called the linear density (mass/unit Length)

• The speed depends only upon the propertiesof the medium – Ex: a denser medium will have less speed

Section 13.9

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Example Problems

• Now go back to the book and look overExample Problems 13.8, 13.9, 13.10

• This will prepare you to do your homework

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