Chapter 20

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Chapter 20

  1. 1. Chapter 20: The Energy of Waves
  2. 3. Animation courtesy of Dr. Dan Russell, Kettering University
  3. 4. What is a wave? (Besides at a ballgame…lol) <ul><li>Any disturbance that transmits energy through matter or space </li></ul><ul><li>Where are they? </li></ul><ul><li>a. in the ocean </li></ul><ul><li>b. microwave ovens </li></ul><ul><li>c. light waves from the sun </li></ul><ul><li>d. sound waves </li></ul><ul><li>e. radio waves </li></ul>
  4. 5. What do waves carry? <ul><li>ENERGY!!! </li></ul><ul><li>Waves do not move particles. </li></ul>
  5. 6. Some waves need help to travel… <ul><li>A medium is a substance through which a wave can travel. </li></ul><ul><li>A medium can be a solid, liquid, or gas. </li></ul><ul><li>What waves need a medium? </li></ul><ul><li>a. sound </li></ul><ul><li>b. ocean waves </li></ul><ul><li>What are these waves called that require a medium? Mechanical Wave </li></ul><ul><li>Waves that do not require a medium are called electromagnetic waves. </li></ul>
  6. 7. How waves travel: <ul><li>Transverse: particles move up and down perpendicular to direction of the wave </li></ul><ul><li>Longitudinal Waves (also called Compressional Waves): particles vibrate back and forth along the path of the wave travels </li></ul><ul><li>Surface Waves: combination of transverse and longitudinal waves </li></ul>
  7. 8. Section 2:Properties of Waves
  8. 9. B. Transverse Waves <ul><li>Wave Anatomy </li></ul>corresponds to the amount of energy carried by the wave crests troughs wavelength wavelength amplitude amplitude nodes
  9. 10. C. Longitudinal Waves <ul><li>Wave Anatomy </li></ul>Amount of compression corresponds to amount of energy  AMPLITUDE. rarefaction compression wavelength wavelength
  10. 11. Longitudinal Wave <ul><ul><li>Compression - dense regions- like the crest of a transverse wave </li></ul></ul><ul><ul><li>Rarefaction- less dense regions- like the trough of a transverse wave </li></ul></ul>
  11. 12. Properties of Waves <ul><li>Amplitude: maximum wave height from the rest position; larger amplitude = more energy </li></ul><ul><li>Wavelength: distance between crest to crest or trough to trough; compression to compression or rarefaction to rarefaction </li></ul>
  12. 13. Waves <ul><li>The more energy a wave carries, the greater its amplitude </li></ul><ul><ul><li>High amplitude in compressional waves means that medium is pushed together more at the compressions </li></ul></ul><ul><ul><li>High amplitude in transverse waves means taller crests and deeper troughs </li></ul></ul><ul><ul><li>http://www.sfu.ca/sonic-studio/handbook/Amplitude.html </li></ul></ul><ul><ul><li>http://id.mind.net/~zona/mstm/physics/waves/introduction/introductionWaves.html </li></ul></ul>
  13. 14. Waves <ul><li>The amplitude of compressional waves is related to how tightly the medium is pushed together at compression </li></ul><ul><li>Denser compressions = larger amplitude = more energy </li></ul><ul><li>Less dense rarefactions = lower amplitude = LESS energy </li></ul>
  14. 15. Properties of Waves… <ul><li>Frequency: the number of waves produced in a given amount of time; measured in hertz (Hz); 1 Hz = 1 wave per second (1 Hz = 1/s); higher frequency means higher energy </li></ul><ul><li>Period: the time it takes for a complete vibration </li></ul>
  15. 16. D. Measuring Waves <ul><li>Velocity ( v ) </li></ul><ul><ul><li>speed of a wave as it moves forward </li></ul></ul><ul><ul><li>depends on wave type and medium </li></ul></ul>v =  × f v : velocity (m/s)  : wavelength (m) f : frequency (Hz)
  16. 17. D. Measuring Waves <ul><li>EX : Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz. </li></ul>WORK: v =  × f v = (3.2 m)(0.60 Hz) v = 1.92 m/s GIVEN: v = ?  = 3.2 m f = 0.60 Hz  v f
  17. 18. D. Measuring Waves <ul><li>EX : An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency? </li></ul>WORK: f = v ÷  f = (5000 m/s) ÷ (417 m) f = 12 Hz GIVEN:  = 417 m v = 5000 m/s f = ?  v f
  18. 19. Waves <ul><li>Light waves travel faster in gases and vacuums than in liquids and solids </li></ul><ul><ul><li>Radiation moves faster when particles are not in the way </li></ul></ul><ul><li>Why are some earthquakes very damaging and other barely felt? </li></ul><ul><ul><li>Depends on the energy of the wave. </li></ul></ul>
  19. 20. Waves <ul><li>Amplitude of transverse waves </li></ul><ul><li>Distance from crest or trough of a wave to the rest position of the medium </li></ul><ul><li>Higher ocean waves = more energy! </li></ul>
  20. 21. <ul><li>Breaking a glass with sound- resonance: http://www.teachersdomain.org/resources/lsps07/sci/phys/energy/glassbreak/index.html </li></ul><ul><li>Sound from sand dunes: http://www.teachersdomain.org/resources/hew06/sci/phys/maf/boomsand/index.html </li></ul><ul><li>Light as particles: http://www.teachersdomain.org/resources/phy03/sci/phys/fund/uncertainty/index.html </li></ul>
  21. 22. Wave Interactions
  22. 23. Wave Interactions… Reflection <ul><li>Reflection : occurs when a wave bounces back after striking a barrier </li></ul><ul><li>All waves can be reflected. </li></ul><ul><li>Reflected sound waves are called echoes . </li></ul><ul><li>Sunlight is being reflected off of the moon at night. </li></ul><ul><li>Water waves reflect off a shoreline. </li></ul>
  23. 24. More wave interactions… <ul><li>Refraction is the bending of a wave as it passes at an angle from one medium to another. Speed of refraction depends on the medium. </li></ul>
  24. 25. Wave interactions… <ul><li>Diffraction: the bending of waves around or through an opening; diffraction depends on wavelength and the size of barrier/opening </li></ul>
  25. 26. Last wave interaction… <ul><li>Interference : the result of 2 or more waves overlapping. </li></ul><ul><li>a. constructive interference : increases the amplitude of a wave </li></ul><ul><li>b. destructive interference : decreases the amplitude of a wave </li></ul><ul><li>Great diagram of waves </li></ul><ul><li>http://www.sciencejoywagon.com/physicszone/09waves/ </li></ul>
  26. 27. More on interference waves <ul><li>Can create standing waves </li></ul><ul><li>Standing wave is a wave that forms a stationary pattern in which portions of the wave are at the rest position. </li></ul><ul><li>Standing waves have nodes and antinodes. </li></ul>
  27. 28. Standing Waves
  28. 29. Interference Waves can be deadly! July 1, 1940- Tacoma Bridge Accident

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