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Wave

Wave. Transfers Energy Without Transferring Matter. Wave. A wave can be described as a disturbance that travels through a medium from one location to another location. There are three types of waves:. Mechanical waves require a material medium to travel (air, water, ropes).

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Wave

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  1. Wave Transfers Energy Without Transferring Matter

  2. Wave • A wave can be described as a disturbance that travels through a medium from one location to another location.

  3. There are three types of waves: • Mechanical waves require a material medium to travel (air, water, ropes). • Electromagnetic waves do not require a medium to travel (light, radio). • Matter wavesare produced by electrons and particles.

  4. Mechanical Waves • Transverse wavescause the medium to move perpendicular to the direction of the wave. • Longitudinal wavescause the medium to move parallel to the direction of the wave. • Surface wavesare both transverse waves and longitudinal waves mixed in one medium. (Such as water waves) • Torsional wavesproduce a twisting motion through the medium – such as the ones which caused the collapse of the Tacoma Narrows Bridge.

  5. Tacoma Narrows BridgeTorsional Oscillation Mechanical Universe Video

  6. Transverse & Longitudinal Waves • In a transverse wave, the particles of the medium oscillate perpendicular to the direction of wave travel. • In a longitudinal wave, the particles of the medium oscillate along the direction of wave travel.

  7. 3 Types of Mechanical Waves

  8. Wave Tutorial Links • http://library.thinkquest.org/10796/ch8/ch8.htm • http://www.physicsclassroom.com/Class/waves/wavestoc.html

  9. Longitudinal Tuning Fork Wave • Vibrating tines produce an alternating pattern of high pressure and low pressure regions. • This pattern travels away from the fork. • Compression – high pressure • Rarefaction – low pressure

  10. Period: T • The PERIOD of a wave is the time for a particle of the medium to complete one oscillation. • The SI unit for period is the second.

  11. Frequency: f • The FREQUENCY of a wave is the number of cycles per unit time. • The unit is Hertz (Hz) which is a cycle per second. • FREQUENCY is also the reciprocal of the period.

  12. Amplitude: A • The AMPLITUDE of a wave is the maximum distance of a particle from the equilibrium position. • The SI unit for amplitude is meter

  13. Wavelength: l (lambda) • The WAVELENGTH of a wave is the length of one complete cycle. • It is the distance between two consecutive “in phase” points. • In phase points are those that are moving in step with each other.

  14. Wave Applets • Wavelength, Amplitude, Phase • Frequency, Wavelength, Speed • Longitudinal Wave • Transverse Wave • Superposition Principle 1 • Superposition Principle 2

  15. Wave Equation • The speed of a wave is equal to the product of the wave’s frequency and wavelength. • v: wave speed • f: frequency • l : wavelength

  16. Speed of Wave on String

  17. Sound Waves • The origin of any sound is a vibrating object • Usually the frequency of the sound is the same as that of the vibrating object • Frequency Range: Sound: 20 Hz – 20,000 Hz Ultrasound: >20,000 Hz Infrasound: < 20 Hz

  18. Forced Vibration & Resonance • forced vibration – example -- strike tuning fork and hold the stem against the table • sounding board -- used to amplify sound in music boxes and all string • resonance -- when the frequency of forced vibrations matches the object's natural frequency, a dramatic increase in amplitude occurs

  19. Speed of Sound

  20. Speed of Sound in Air • depends on wind conditions, temperature, and humidity • does NOT depend on loudness or frequency of the sound • all sounds travel at the same speed in the same medium in dry air at 0°C ~ 331 m/s (1200 km/h) (740 mi/h) • Sound travels faster through warm air than cold air. • In air, vsound = 331.4 m/s + (0.6 m/s/Co)*TC

  21. Distance to Lightning • Light travels at 3 x 108 m/s in air • Sound travels at about 330 m/s in air at 0oC • It takes about 5 seconds for the sound (the thunder) to travel 1 mile. • Count the seconds between the flash and the sound, divide by 5, and you have the approximate distance in miles to the lightning.

  22. Pitch & Loudness • Pitch – frequency Double frequency – go up an octave • Loudness – amplitude • Units – W/m2

  23. Human Ear

  24. Decibel Scale • incredibly sensitive • can hear everything from fingertip brushing lightly over fabric to a loud jet engine • sound of jet engine is about 1012 times more powerful than smallest audible sound • a big difference! • decibel scale -- smallest audible sound is 0 dB • A sound 10 times more powerful is 10 dB • A sound 100 times more powerful than near total silence is 20 dB Decibel Scale is logarithmic

  25. Sound Intensities (W/m2)

  26. Intensity Level • Logarithmic Scale • Dimensionless • I0 = 10-12 W/m2

  27. Decibel Levels • Near total silence - 0 dB • A whisper - 15 dB • Normal conversation - 60 dB • A lawnmower - 90 dB • A car horn - 110 dB • A rock concert or a jet engine - 120 dB • A gunshot or firecracker - 140 dB

  28. Doppler Effect • Doppler Effect Lesson

  29. Doppler Effect • Moving Source Moving Observer • General Expression

  30. Superposition Principle • Wave interference occurs when two or more waves act simultaneously on a medium. • Whenever two or more waves pass through each other, the resulting disturbance at a given point in the medium may usually be found by adding the individual displacements that each wave would have caused. (Principle of Superposition)

  31. Constructive Interference • Constructive interference occurs when the waves are trying to displace the medium in the same direction.

  32. Destructive Interference • When these two waves are completely overlapping, there will be complete destructive interference. • Destructive interference occurs when the waves are trying to displace the medium in opposite directions.

  33. Pulse/Wave Reflection • Fixed/Free End Reflection of Sine Wave Fixed End Reflection Free End Reflection Interference between incident and reflected pulse in a fixed end reflection

  34. Standing Waves • For certain frequencies, the interference of the incident and reflected waves results in a standing wave pattern.

  35. Fundamental Frequencyand Harmonics

  36. Standing Waves in a Tube • Closed on one end: • Open on both ends:

  37. Waves Moving in and Out of Phase • When the 2 waves are in phase, the resulting disturbance has a maximum amplitude. • When the 2 waves are out of phase, the resulting disturbance has a minimum amplitude.

  38. Beats • Waves of slightly different frequencies form a pattern of alternating maximum and minimum amplitude. • The packets of maximum amplitude are called beats.

  39. Noise Canceling • tiny microphones, one on each earpiece, detect ambient noise before it gets to your ears. • noise-cancellation circuitry inverts the captured signal, turning the noise's sound wave upside down. • noise-cancellation system adds the sonic opposite of the external noise to whatever you're listening to • eliminating most of the pollution and leaving you with just your music.

  40. Standing Waves • http://phet.colorado.edu

  41. Fundamental & Harmonics

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