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A wave is a wave is a wave

A wave is a wave is a wave. An introduction to waves. What are some types of waves?. Water Sound Light Matter Sports fans Earthquakes/seismological Hand?. What distinguishes waves?. Water, Sound, Light, Sports Fans, quakes Information moves without individual particles carrying it.

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A wave is a wave is a wave

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  1. A wave is a wave is a wave An introduction to waves

  2. What are some types of waves? • Water • Sound • Light • Matter • Sports fans • Earthquakes/seismological • Hand?

  3. What distinguishes waves? • Water, Sound, Light, Sports Fans, quakes • Information moves without individual particles carrying it

  4. What is a wave? - Webster says... • a moving ridge or swell [on a surface of water] • a swell, surge, or rush • any surging or progressive movement resembling a wave of the sea • Physics. a progressive disturbance propagated from point to point in a medium or space without progress or advance by the points themselves

  5. What is a wave? - Dr. DJ says • the method of transmitting information/energy/etc. from point A to point B without individual objects traveling between the points

  6. Transverse waves • Water wave: water moves up and down, wave moves toward shore • Rope: string moves up and down, wave moves toward end • Sports fans: fans rise and sit, wave moves around stadium • Electromagnetic (light): fields vary in a direction perpendicular to motion

  7. Longitudinal waves • Slinky: Coils compressed and released create wave in direction of compression • Sound: Air compresses in direction of motion, but molecules don’t travel from source to ear

  8. -f A A A A A=Amaxsin(2px/l) A=Amaxsin(2px/l) A=Amaxcos(2px/l + f) l The sinusoidal (in space) “wave” • One wavelength occupies 2p radians • Described by A=Amaxcos(2px/l) x

  9. A T The sinusoidal (in time) “wave” • A cycle completes in one “period,” which occupies 2p radians • Described by A=Amaxcos(2pt/T+f) A=Amaxsin(2pt/T +f) t

  10. Wave vocabulary • wavelength l = distance per cycle • wave numberk= radians per distance 2p/l = rad/cycle (cycle/m) = rad/m = k • period T = time per cycle • angular frequency w = radians per second 2p/T = rad/cycle (cycle/s) = rad/s = w • frequencyf= number of cycles per second f = cycles/second = 1/(second/cycles) = 1/T • Speed v = distance per time; wave travels l in T v = l/T

  11. The traveling wave • A wave varies in both space and time: • At one location, the amplitude varies in time • At one time, the amplitude varies in space • A sinusoidal wave moving toward positive x is described by A = Amaxcos(kx – wt + f) • A sinusoidal wave moving toward negative x is described by A = Amaxcos(kx + wt + f) Animation of traveling waves

  12. Do the Before You Start part of the activity Think about the questions by yourself for ~5 minutes, then work with your assigned group to answer the questions. You should finish in about 15 more minutes. Each group member should fill out his or her own activity sheet.

  13. Do We All Agree? • What is the frequency of the wave? • How can we sketch a graph of the wave without resorting to graphing calculators/software? • How does this graph change when we change the phase constant? • What are the differences between a graph of V vs. t and a graph of V vs. x?

  14. Do the rest of the activity Your instructor will point out a few features of the equipment. After this has been done, work with your assigned group to complete the activity. You should finish in ~40 minutes.

  15. What have we learned today? • Waves transmit information between two points without individual particles moving between those points • Transverse Waves oscillate perpendicularly to the direction of motion • Longitudinal Waves oscillate in the same direction as the motion • The spatial dependence of periodic waves can be described by either the wavelength l or the wave number k, which are related. • The time dependence of periodic waves can be described by either the period T, the angular speed w, or the frequency f, which are all related.

  16. What else have we learned today? • Any traveling sinusoidal wave may be described by y = ym sin(kx wt + f) • f is the phase constant that determines where the wave starts.

  17. Before the next class, . . . • Read the Assignment on Waves found on WebCT • Read the Assignment on Reflection and Refraction using on-line tutorial (start from WebCT Contents) • Do Reading Quiz 1 which will be posted on WebCT by Tuesday.

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