1. CHAPTER 15 : CHARACTERISTICS OF WAVES

2. What are Waves? Waves Wave = a disturbance that transfers energy from place to place. – Remember, energy = the ability to do work!

3. The disturbance caused by a wave is only temporary.

4. What carries Waves? Medium = the material through which a wave travels. – Gases, liquids, & solids all act as mediums

5. Mechanical waves = waves that require a medium through which to travel. -Waves do not carry the medium itself with them. Waves travel through the water but don’t carry the water with them. How does the duck show this?

6. What Causes Waves? Waves are created when a source of energy causes a medium to vibrate. Vibration = a repeated back and forth or up-down motion. – The motion is the source of the wave!

7. What is the source of vibrations in this picture?

8. A moving object has energy. The moving object can transfer energy to a nearby medium, creating a wave. – Ex: As propellers of a boat turn, they disturb the calm water surface. The boat’s propellers transfer energy to the water. The propeller produces a wave that travels throughout the water. As the boat moves through the water, it also causes waves.

9. What might have caused this disturbance? What is the medium?

10. Types of Waves Waves are classified by how they move. The 3 types are: – Transverse – Longitudinal – Surface

11. Transverse Waves Transverse Waves = waves that move the medium at right angles to the direction in which the waves are traveling (Ex. The wave on a rope). As a transverse wave moves in one direction, the particles of the medium move across the direction of the wave.

12. The highest parts of the wave are crests. The lowest parts are troughs. Direction of wave

13. Longitudinal Waves Longitudinal waves move the particles of the medium parallel to the direction that the waves are traveling (Ex. Coils in a Slinky). Compressions = the parts where the coils are close together. Rarefractions = the parts where the coils are spread out, or rarefied.

14. As compressions & rarefactions travel along the Slinky, each coil moves slightly forward and then back.

15. The energy travels from one end of the Slinky to the other, creating a wave. After the wave passes, each part of the spring returns to the position where it started.

16. Combinations of Waves Surface waves are combinations of transverse & longitudinal waves. Occur at the surface between 2 mediums, such as water & air.

17. When waves pass through water, the water (& anything on it) moves up & down, like a transverse wave.

18. Surface waves The water also moves back & forth slightly in the direction that the wave is traveling, like the coils of the Slinky. But unlike the Slinky, water does not compress.

19. The up-and-down & back-and- forth movements combine to make each particle of water move in a circle.

20. How would waves affect the motion of a ship?

21. Properties of Waves Section 15 - 2 Basic properties of waves: amplitude wavelength frequency speed

22. Amplitude Is the maximum distance the particles of the medium carrying the wave move away from their rest positions. A measurement of how much a particle in the medium is disturbed by the wave.

23. Amplitude of a Transverse Wave

24. Amplitude of longitudinal waves - very crowded = large amplitude

25. Amplitude is the LOUDNESS of a sound wave.

26. Wavelength The distance a wave travels before it starts to repeat. The distance between 2 corresponding parts of a wave.

27. The crest of a transverse wave is similar to the compression of a longitudinal wave. Trough/rarefaction Transverse Wave Longitudinal Wave

28. Two characteristics of waves - wavelength & amplitude.

29. Frequency The number of complete waves that pass a given point in a certain amount of time. – Or the number of vibrations per second. – Measured in Hertz (Hz) 1 wave or vibration / second = 1Hz

30. Which set of waves would have the greatest frequency?

31. We hear the frequency of sound waves as pitch.

32. SPEED Different waves travel at different speeds. Speed, wavelength & frequency – are related to each other by a mathematical formula. Speed - wavelength x frequency

33. Speed = wavelength x frequency Frequency = speed / wavelength wavelength = speed / frequency

34. Speed of different types of waves Light travels faster than sound - Thunder & lightning

35. Speed in different mediums Waves in different mediums travel at different speeds. – Sound waves traveling through air at the same pressure & temperature, travel at the same speed. – But if the temp or pressure change, the speed of waves change also.

36. Speed & change of frequency If you increase frequency then wavelength must decrease.

37. Sec. 3: Interactions of Waves There are 5 main types of interactions of waves: – Reflection, – Refraction, – Diffraction, – Interference, & – Standing waves

38. Reflection Reflection = when an object or wave hits a surface through which it cannot pass, it bounces back. – Ex: Ball that hits a wall & bounces back Echoes are reflected sound

39. Draw this diagram in your notes!

40. Angle of Incidence = the angle between the incoming wave & the imaginary perpendicular line. Angle of Reflection = the angle between the reflected wave & the imaginary line.

41. Law of Reflection Law of Reflection states that the angle of reflection equals s the angle of incidence. All waves obey the law of reflection.

42. Refraction When a wave moves from one medium into another medium at an angle, it changes speed as it enters the second medium, which causes it to bend. The bending of waves due to a change in speed is called refraction.

43. All waves change speed when entering a new medium, they don’t always bend. – Bending occurs when one side of the wave enters the new medium before the other side of the wave. The side that enters 1 st changes speed first. The other side is still traveling at its original speed. – Bending occurs because the 2 sides of the wave are traveling at different speeds.

44. Have you every pushed a shopping cart that had a very stiff wheel? – Was it easy to push? – Was it easy to control the direction of the cart? How is this example related to refraction?

45. Diffraction When a wave passes a barrier or moves through a hole in a barrier, it bends and spreads out. Diffraction = the bending of waves around the edge of a barrier.

46. A wave can go through a hole in a barrier & spread out

47. Or, a wave can bend around a corner.

48. Interference When 2 or more waves meet, they have an effect on each other. This interaction is called interference. 2 types of interference: – Constructive – Destructive

49. Constructive Interference Occurs whenever 2 waves combine to make a wave with a larger amplitude. – Waves “helping each other” to give a stronger result, adding energy

50. Notice how the crests & troughs are aligned. This allows them to “add” together.

51. Destructive Interference Occurs when the amplitudes of 2 waves combine with each other producing a smaller amplitude.

52. Notice when the crests of one wave align with the troughs of another, they cancel each other out.

53. If one wave travels a little behind the other, they combine both constructively & destructively at different places.

54. Standing Waves Standing wave is a wave that appear to stand in one place, even though it is really 2 waves interfering as they pass through each other.

55. Nodes - at certain points, destructive interference causes the 2 waves to combine to produce an amplitude of zero. The crests & troughs of the standing wave are called antinodes. – These are the points of maximum energy!

57. When an object is vibrating at a certain frequency, it takes very little energy to maintain or increase the amplitude of the wave. – Ex. If you are pushing a child on a swing, once you get it started, it takes very little energy to keep it going.

58. Most particles have a natural frequency of vibration Resonance occurs when vibrations traveling though an object match the object’s natural frequency. An object that is traveling at its natural frequency absorbs energy from objects that vibrate at the same frequency.

59. Did you know that marching troops could crash a bridge? Why? If an object is not very flexible, resonance can cause it to shatter. If all the troops march across the bridge in perfect step, it is possible that the pounding could match the natural frequency of the bridge. The increased vibration could cause the bridge to collapse. Tacoma Narrows For this reason, troops are told to break step when crossing bridges!

60. Interactions of Waves Refraction– when a wave moves from deep water to shallow water at an angle, it bends, or refracts.

61. Interactions of Waves Diffraction = when waves pass an obstacle, they diffract, bending & spreading out around & behind the obstacle.

62. Interactions of Waves Constructive Interference – when 2 waves combine to make a wave with a larger amplitude.

63. Interactions of Waves Destructive Interference = when 2 waves combine to make a wave with a smaller amplitude. Constructive Interference

64. Interactions of Waves Reflection – when a wave hits a barrier, it reflects at the same angle that it hit the barrier.

65. Seismic Waves An earthquake occurs when rock beneath Earth’s surface moves. This movement creates stress in the rock. When the stress in the rock builds up enough, the rock breaks or changes shape, releasing energy in the form of waves or vibration.

66. Giant wave reaching the coast of Java. The wave was caused by earthquakes related to the eruption of Krakatau volcano - 40Km away!

67. The waves produced by earthquakes are known as seismic waves. Seismic waves ripple out in all directions from the point where the earthquake occurred. As the waves move, they carry the energy through Earth. 3 types of Seismic waves: – Primary, Secondary, & Surface

68. Primary Waves Primary waves (P waves) = longitudinal seismic waves. Move faster than other seismic waves & arrive at distant points before other seismic waves. Composed of compressions & rarefactions of rock inside Earth.

69. Secondary Waves Secondary Waves ( S waves) = transverse seismic waves with crests & troughs. Cannot travel through liquids. – Since part of Earth’s core is liquid, S waves don’t travel directly through Earth.

70. Which type of wave can scientists generally detect on the side of Earth opposite an earthquake? Mainly P waves since they can travel through liquids ( the core of the Earth) and S waves cannot.

71. Surface Waves When P & S waves reach Earth’s surface, some of them are transformed into surface waves. – Remember, surface waves are a combination of longitudinal & transverse waves. Travel more slowly than either P or S waves, but they produce the most severe ground movements.

72. Why don’t S waves travel through the Earth’s core?

73. Earthquakes that occur underwater can cause huge surface waves on the ocean called tsunamis. – Tsunamis can cause great damage when they reach land!

74. Detecting Seismic Waves Seismograph = instrument used to detect & measure earthquake waves. A seismograph records the ground movements caused by seismic waves as they move.

75. Scientist studying the printout from the seismograph. Seismograph

76. How do seismographs work? They measure the time between the arrival of the __?__waves & the __?___waves, scientist can tell how far away the earthquake was. They then compare reading from at least 3 seismographs at different places on Earth, in order to determine where the earthquake occurred.

77. How might earthquakes be used to locate mineral resources? Geologists may set off explosives to produce a small earthquake. The seismic waves from the explosion reflect from structures deep underground to seismographs located around the site of the explosion.