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Announcements -Homework 21: due Tuesday, Nov. 30, 2004 -Review session before final

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Waves are closely related to oscillations We’ll mainly deal with sinusoidal waves. - Water waves: Water molecules oscillate in a circle - Sound waves: Air molecules oscillate back and forth - Stadium waves: People move up and down - Electromagnetic wave: (in Physics 114) Chapter 16: Waves-I Reading assignment: Chapter 17 Homework :(due Friday, Nov. 11, 2004): Problems:Q3, Q12, 7, 8, 13, 31, 34, 35, 47

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Waves : Propagation of a disturbance through a medium “Wave flees the place of its creation, while water [particle] does not” - Water waves: Water molecules oscillate up and down - Sound waves: Air molecules oscillate back and forth - Stadium waves: People move up and down All waves carry (propagate) energy

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Traveling waves Transverse waves: The particles of the disturbed medium move perpendicular to the wave motion particle wave

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Traveling waves Longitudinal waves: The particles of the disturbed medium move parallel to the wave motion

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Examples of waves: “Bump” traveling down a rope:___________________ Compression of a slinky:_____________________ Sound waves:____________________ La ola in a stadium (getting up/sitting down):_____________ Water wave: ____________________________

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Basic Variables of Wave Motion Terminology to describe waves - Crest: “Highest point” of a wave - Wavelength : Distance from one crest to the next crest. - Wavelength : Distance between two identical points on a wave. - Period T: Time between the arrival of two adjacent waves. - Frequency f: 1/T, number of crest that pass a given point per unit time

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Sinusoidal waves Brown curve: Snap shot at time t = 0 Blue curve: Snap shot at later time.

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Sinusoidal waves The function describing a traveling sinusoidal wave:

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Sinusoidal waves

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Black board example 17.1 Traveling sinusoidal wave (a)Find the wave number k, the period T, the angular frequency and propagation speed v of the wave. (b)If the vertical displacement of the medium at t = 0 and x = 0 is also 15.0 cm, what is the phase constant ? (c)Write a general expression for the wave function. A sinusoidal wave traveling in the positive x- direction has an amplitude of 15.0 cm, a wavelength of 40.0 cm, and a frequency of 8.00 Hz.

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Transverse wave: Speed of wave Speed of waves on a string Where: T… tension in rope (don’t confuse with period T) … mass per unit length of rope

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Black board example 17.2 Speed of pulse in cord A uniform cord has a mass of 0.300 kg and a length of 6.00 m. The cord passes over a pulley and supports a 2.00 kg object as shown. (a) Find the speed of a pulse traveling along this cord. (b) Find the time it takes the pulse to travel from the wall to the pulley

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