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**Unformatted text preview: **1 Physics 6B Wave Motion 2 Housekeeping • Exams will be returned Friday ! of what’s been graded so far, scores range from 100% to 32% ! median of ~79% • Second midterm is 2/28 ! it will be shorter (probably 3 questions with 3-4 parts and fewer calculations). 3 Wave motion • For wave of form y(x,t) = f(x-vt) ! pattern travels down x-axis ! energy travels down x-axis ! material moves back and forth » no net motion along x-axis • Transverse waves: ! “back and forth” motion (oscillation) perpendicular to direction of pattern motion • Longitudinal waves: ! oscillation in same direction as pattern motion A wave is a traveling disturbance that transports energy but not matter 4 Traveling waves • f(x) describes some wave shape when you take a snap shot at t = 0 • f(x - vt) describes that shape traveling in the + direction along the x- axis with speed v • f(x + vt) describes that shape traveling in the – direction along the x- axis with speed v 5 Clicker question • A pulse traveling along the x-axis has the form: If v = 5 m/sec, when does the peak of the pulse pass x=10m? A. t = 0 B. t = - 2 sec C. t = 2 sec D. t =- 0.5 sec E. t = 0.5 sec 6 Clicker question • A pulse traveling along the x-axis has the form: If v = 5 m/sec, when does the peak of the pulse pass x=10m? A. t = 0 B. t = - 2 sec C. t = 2 sec D. t =- 0.5 sec E. t = 0.5 sec " 7 Simple harmonic waves • Wave shape is a sine or cosine… ! speed v, amplitude A , wavelength ! (“lambda”), period T • Snapshot of a cosine wave at t=0: • Re-writing to show traveling in time...

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