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Spring 2007 – Week 3 PHY 131 1

Week 3

All about waves…

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One Mass

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Two Masses

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Two Masses

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Three Masses

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Many Masses

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What is a Wave?

• Some Examples (see Related Links page)

• Longitudinal & Transversal Waves• Superposition of Waves• Reflection of Waves• Refraction of Waves

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About Resonance

• Resonance (Amp & phase)

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Refraction

• Due to change in wave velocityfrom one medium to another

• Refraction of Waves

• Refraction (Java Applet)

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The Effect of Temperature

How does the speed of sounddepend on the temperature?

Kinetic Gas Model

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Continuous Refraction

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Thermal Inversion & RefractionThermal inversion (e.g. night time).Air is cooler near ground Continuous

Refraction

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Thermal Gradient & Refraction

Usually, the air nearest the ground is hottest.This creates an upward refraction of sound

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Shouting against the Wind

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The Wavelength of Sound

v = fλ λ =vf

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Diffraction of Waves

Ability of waves to go aroundobstacles or spread out aftergoing through an opening

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Diffraction of Waves

Key: Size of wavelength compared to opening or obstacle

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Diffraction of Waves

Ability of waves to go aroundobstacles or spread out aftergoing through an opening

Ripple Tank with Walls

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Listen to the Band

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This is what you hear in from a cross street

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It is because of Diffraction

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Adding Waves and Waves…

•Superposition of waves•Beats•Ripple Tank•Tuning Fork Demonstration•Acoustic Interference

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Standing Waves

Recall Wave Superposition