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Waves

Waves. Waves . Definition of wave A disturbance that transfers energy through matter or space “Disturbance”-a change from a normal state. Periodic or Harmonic Motion. Motion that repeats itself in the same amount of time One repetition of motion called a cycle Examples?

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Waves

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  1. Waves

  2. Waves • Definition of wave • A disturbance that transfers energy through matter or space • “Disturbance”-a change from a normal state

  3. Periodic or Harmonic Motion • Motion that repeats itself in the same amount of time • One repetition of motion called a cycle • Examples? • What does graph look like?

  4. Periodic or Harmonic Motion • Amount of time to complete cycle called a period (T) • Frequency (f) is how many complete cycles occur in one second • T = 1/f or f =1/T • Amplitude is the amount of displacement from rest

  5. Graphing harmonic motion http://www.mcanv.com/pend1.html

  6. Graphing Harmonic Motion http://www.gailruby.com/Picture4.png http://en.wikipedia.org/wiki/File:Simple_harmonic_oscillator.gif

  7. Homework • Complete Harmonic Motion Worksheet

  8. Waves demonstrate harmonic motion • Wave movement through matter • Particles move • Particles return to original position (location) http://upload.wikimedia.org/wikipedia/commons/7/74/Simple_harmonic_motion_animation.gif

  9. Types of Waves Based on particle motion in wave 2 types • Transverse • Longitudinal

  10. Wave Type-Transverse • Particle motion perpendicular to wave direction http://upload.wikimedia.org/wikipedia/commons/6/6d/Onde_cisaillement_impulsion_1d_30_petit.gif

  11. Wave Type-Transverse • Particle motion perpendicular to wave direction http://www.kettering.edu/~drussell/Demos/waves-intro/waves-intro.html

  12. Parts of a Transverse Wave http://library.thinkquest.org/15433/unit5/transv1.gif

  13. Examples of Transverse Waves • Shaking a string • Ocean waves • Ripples on a pond • “Stadium” or human wave • Electromagnetic (radio, light, micro ect…)

  14. Wave Type-Longitudinal • Particle motion in direction of wave http://en.wikipedia.org/wiki/Image:Onde_compression_impulsion_1d_30_petit.gif

  15. Wave Type-Longitudinal • Particle motion in direction of wave

  16. Parts of a Longitudinal Wave • Particle motion in direction of wave

  17. Examples of Longitudinal Waves • Sound waves • Oscillating springs

  18. Sound waves are longitudinal waves http://emusictips.com/wp-content/uploads/2009/03/sound_waves_animated.gif

  19. Represent longitudinal waves as transverse waves • Particle displacement in a longitudinal wave can be graphed as a transverse wave • Particle motion from rest graphed as amplitude http://faraday.physics.utoronto.ca/IYearLab/Intros/StandingWaves/Flash/long_wave.html

  20. Sound Waves • Sound waves move vibrational energy through matter • Sound waves are longitudinal waves

  21. Wave Properties • Common Characteristics of Wave • Length • Height • Frequency (how often they occur) • Period (how long to make 1 cycle) • Speed • All Characteristics of Waves Can Vary

  22. Wave Characteristics • Wavelength (λ)-the distance between repeating parts of a wave • Trough to trough • Peak to Peak • Rarefaction to Rarefaction • Compression to compression - Or any other repeating part

  23. Wave Characteristics • Wave amplitude (height)-the maximum displacement from the undisturbed position of the medium to the top of a crest or bottom of a trough

  24. Check Your UnderstandingTransverse Waves • The wavelength of the wave in the diagram above is given by letter ______. • The amplitude of the wave in the diagram above is given by letter _____.

  25. Check Your UnderstandingTransverse Waves • Indicate the interval which represents one full wavelength.

  26. Wave Characteristics • The frequency(f) of a wave is the number of complete waves (cycles) that pass the observer in a given time. • Hertz is the unit of frequency, and just means how many cycles (peaks) per second.

  27. Wave Characteristics • The period (T) of a wave is the time for a wave to make one complete cycle (peak to peak). • The period is related to the frequency by the following equation f=1/T

  28. Wave Characteristics • The speed (v) of a wave is the how fast the wave is moving • distance the wave travels in a certain amount of time.

  29. Wave Characteristics • The relationship between the speed, frequency, period and wavelength • Example: • 2 waves each second (i.e. frequency = 2 Hz) • the period is equal to 1/f = ½ second • the distance between the waves as 25 cm: this is the wavelength. • In 0.5 s, waves move 25 cm, so we can find the speed using: speed= v = λ x f = 25 x 2 = 50 cm/sec OR speed = v = λ x 1/T = 25 x (1÷ ½) = 50 cm/sec

  30. Homework • Complete Wave Worksheet

  31. Factors Affecting the Speed of Sound • Sound waves require matter to travel • No particles to compress = no waves = no sound • Speed of sound depends on matter or medium • Speed does not depend of the source • Factors that affect the speed of sound include: • Temperature of medium • Elasticity of medium • Density of medium

  32. Speed of Sound • Temperature Affects • Temperature changes affect sound speed more in gases than solids or liquids • Particles spaced apart in gases • Temperature affects spacing of particles in gases (Charles & Boyles Gas Laws) • Temperature • High temperature air = higher sound speed • Low temperature air = lower sound speed • Heat and sound = kinetic energy

  33. Speed of Sound • Elasticity • Elasticity = The tendency of an object to return to its original shape once the forces are no longer applied. • Phases of matter have great effect on elasticity of matter • Greater elasticity = Greater speed of sound • vsolids > vliquids > vgases

  34. Speed of Sound • Density • Less effect on speed of sound than elasticity • Within a single phase of matter = greater impact • Density = mass/volume • Within a single phase of matter • Greater density = lower speed of sound • Mass of heavier particles are harder to move • Greater density = Greater inertia

  35. Speed of Sound • Materials • The speed of sound varies through different materials

  36. Sonic Boom • When an object travels faster than the speed of sound it breaks the “sound barrier” • Waves all traveling at same speed, pile up on each other as plane pushes them together • Result is a “sonic boom”

  37. Properties of Sound • Intensity-measure of sound’s amplitude • Related to loudness, but loudness is subjective • Intensity measured in decibels (dB) • Increase in 10 dB results in sound that is twice as loud

  38. Properties of Sound • Frequencyand Pitch • Frequency is number of waves in a certain amount of time • Frequency is measured in Hertz (Hz) • Pitch is related to frequency, describes how high or low the sound is. Pitch is subjective. • Pitch is the sensation of frequencies • High frequency = high pitched sounds • Low frequency = low pitched sounds

  39. Human Hearing and Frequency • Humans can hear frequencies ranging from 20-20,000 Hz • Ultrasound are sound waves with frequencies above the human hearing range

  40. Properties of Sound • Sound Quality is referred to Timbre • Differences in timbre allow listeners to hear not only the difference between an oboe and a flute, but also the difference between two different flutes, even if both flutes are playing notes at the same frequency and amplitude

  41. Descriptions related to timbre Reedy Brassy Clear Rounded Piercing Strident Harsh Warm Mellow Resonant Dark or Bright Heavy or Light Flat Having much, little, or no vibrato Properties of Sound

  42. Properties of Sound • Doppler Effect • The observed effect between an observer and a sound source when one is moving relative to another • distance decreasing → perceived frequency (pitch) is increased • distance increasing → perceived frequency (pitch) is decreased http://imagine.gsfc.nasa.gov/YBA/M31-velocity/Doppler-shift-2.html

  43. Doppler Effect • Examples • http://www.lon-capa.org/~mmp/applist/doppler/d.htm • (visual) • http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/doppler.htm • (visual and audio)

  44. Wave Interactions • What is the result of collisions between waves and other waves or objects? • Waves transfer energy • Collisions results in energy transfer • Lose or gain energy

  45. Wave Interactions • Wave colliding with other waves cause interference • Principle of Superposition • Waves add (subtract) amplitudes (energy) • Two kinds of interference • Constructive (add) • Destructive (subtract)

  46. Sound Wave Interactions • Interference • Constructive = increase in intensity • Destructive = decrease in intensity

  47. Wave Interactions • Constructive Interference • waves add to produce a new wave with larger peaks than either of the two original waves

  48. Wave Interactions • Constructive interference

  49. Wave Interactions • Destructive Interference • waves add to produce a new wave with smaller peaks than either of the two original waves

  50. Sound Wave Interactions • Interference

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