2. Physics 2016 https://www.youtube.com/watch?v=Wvn0Rs0LRGE

3. Nature of waves Drop a pebble into a still pond and notice the circular waves moving outward. Watch the grass move in a wave-like motion on a windy day

4. Nature of a wave Or when a storm comes in, watch the huge waves in the ocean.

5. So what is a wave? Everything around us wiggles and jiggles, even things we can’t see such as ATOMS vibrates. Vibrations can’t exist in one instant, it has to move back and forth until it dies down. **Just can’t go forward only or backward only! **

6. Tuning fork When you strike a tuning fork the vibrations will continue before it dies down and stops.

7. Waves A wave is a disturbance that transfers energy (NOT MATTER) through matter or space It is important to know that WAVES MOVE THROUGH MATTER, (the medium) the particles of matter do NOT move along with the wave, only the ENERGY that produces the waves move with the wave.

8. Waves through a medium A medium is any substance that a wave must move through. A mechanical wave requires a medium to travel on. Examples: 1. Water (ocean waves) 2. Air (sound waves) Can something travel if there is NO medium?

9. Medium Of course! Can you see the sun and stars? Electromagnetic waves can travel with out a medium. Light can travel through space. Can sound travel through space (vacuum)? NO! it is a mechanical wave Needs a medium!

10. Two properties of medium affect the speed of a wave: Density: waves move slower in a more dense medium. Elasticity: think of a rubber band- it returns back to its original shape. Waves move faster if it’s in a more elastic medium.

11. Parts of the wave:

12. In our wave here the dashed line represents the equilibrium position. (rest point) Once the medium is disturbed, it moves away from this position and then returns to it

13. Parts of the wave crest The points A and F are called the CRESTS of the wave. This is the point where the wave exhibits the maximum amount of positive or upwards displacement

14. Parts of the wave trough The points D and I are called the TROUGHS of the wave. These are the points where the wave exhibits its maximum negative or downward displacement.

15. Parts of the wave: 1. Amplitude – indicated the energy of the wave – or the height of the wave from origin to crest or from origin to trough.

16. Parts of the wave: 2. Wavelength – distance in meters, between 2 consecutive crests or troughs. (must include 1 full crest and 1 full trough) They are the same distance, so it doesn’t matter which one you chose. We use the symbol (lambda)  This is the length of the wave pulse.

17. Parts of the wave: 3. Frequency – is the number of complete waves at a given point (cycle) per time. * We use the unit Hertz or Hz. 1 Hz = 1 wave per seconds On the next slide determine which wave has a higher frequency:

18. Which one has a greater frequency

19. Let’s calculate the speed of a wave: Speed = wavelength X frequency Frequency= waves/time If you have a wave that has a frequency of 4 Hz and wavelength of 2 meters. What is the speed of the wave? Steps: 1. Write the formula 2. Substitute given numbers in the problem 3. Solve for the unknown ( calculate)

20. Let’s calculate the speed of a wave: 1. Write the formula speed = wavelength X frequency s = lambda times f 2. Substitute given numbers in the problem wavelength = 2 meters frequency = 4 Hz 3. Solve for the unknown ( calculate) v = 2 x 4 = 8 m/s

21. Now it’s your turn: What is the frequency of a wave that has a wavelength of 5 meters and a speed of 250 m/sec?

22. Wave Period (T) It is the time it takes for one cycle to complete. It also is the reciprocal of the frequency. T = 1 / f f = 1 / T

23. Wave pulses A wave pulse is a short length of wave, often just a single oscillation.

24. Classifying Waves Transverse waves – the one that we are most familiar with! This is a wave in which the motion of the medium is at right angles to the direction of the wave. It is perpendicular to the movement.

25. Transverse Waves If we tie a rope to the door and hold on to the other end. Moving the rope up and down. Notice the energy is moving along the rope, notice the rope moves up and down while the “wave” moves forward.

26. Transverse Waves

27. Longitudinal Wave There are two part of this wave: Compression- in which the molecules are crowded together. Rarefaction – molecules are spread out. sound is transferred through longitudinal waves.

28. Longitudinal Waves How does this work? The compressed band of (air) will move forward colliding with the molecules next to them. REMEMBER: energy is transmitted as a wave! Surface waves are a combination of transverse and longitudinal waves. Particles follow a circular path.

29. WAVES

31. Recap: Pulse – single bump or disturbance that travels through a medium Continuous Wave – keeps moving! One Wave  Period/frequency – are applied to continuous waves Frequency – is the number of complete oscillations each second Measured in Hertz or waves/seconds

32. Magnitude 7.0 HAITI Tuesday, January 12, 2010 at 21:53:09 UTC Earthquakes!!! Magnitude 7.0 HAITI Tuesday, January 12, 2010 at 21:53:09 UTC A powerful earthquake hit the impoverished country of Haiti on Tuesday, collapsing the presidential palace and numerous other critical government buildings and raising fears of substantial casualties in what a witness called “a major, major disaster.” NBC News

33. Perceived Shaking Extreme Violent Severe Very Strong Strong Moderate Light Weak Not Felt Mike Blanpied of the US Geological Survey said that, based on the location and size of the quake, about three million people would have been severely shaken by its impact.

35. Aftershocks This earthquake was followed by five powerful aftershocks within the first two hours after the devastating quake. Left: Aftershocks (yellow) In the first eleven hours after the earthquake there have been 32 aftershocks greater than magnitude 4.

36. Earthquake It is produced by sudden motion of rock masses within the Earth’s crust. The seismic waves of energy radiate outward. These seismic waves causing the shaking/trembling are known as EARTHQUAKES!!! **** MOST earthquakes do NO damage at all, very FEW are so extreme!

37. LIGHT An electromagnetic wave is a wave that is capable of transmitting its energy through a vacuum (i.e., empty space). Electromagnetic waves are produced by the vibration of charged particles.

38. A mechanical wave is a wave that is not capable of transmitting its energy through a vacuum. Mechanical waves require a medium in order to transport their energy from one location to another. A sound wave is an example of a mechanical wave. Sound waves are incapable of traveling through a vacuum. Slinky waves, water waves, stadium waves, and jump rope waves are other examples of mechanical waves; each requires some medium in order to exist. A slinky wave requires the coils of the slinky; a water wave requires water; a stadium wave requires fans in a stadium; and a jump rope wave requires a jump rope

39. Behavior of Waves We know that waves travel through mediums. But what happens when that medium runs out? When waves encounters a boundary of the medium it sometimes reflects, passes through, or change direction. (Two or more waves can exist in the same medium)

40. 39 Boundary Behavior The behavior of a wave when it reaches the end of its medium is called the wave’s BOUNDARY BEHAVIOR. When one medium ends and another begins, that is called a boundary.

41. 40 Fixed End Here the incident pulse is an upward pulse. The reflected pulse is upside-down. It is inverted. The reflected pulse has the same speed, wavelength, and amplitude as the incident pulse.

42. 41 Fixed End Animation

43. Free End Another boundary type is when a wave’s medium is attached to a stationary object as a free end. In this situation, the end of the medium is allowed to slide up and down. What would happen in this case?

44. Free End Here the reflected pulse is not inverted. It is identical to the incident pulse, except it is moving in the opposite direction. The speed, wavelength, and amplitude are the same as the incident pulse.

45. Free End Animation

46. 45 Change in Medium Our third boundary condition is when the medium of a wave changes. Think of a thin rope attached to a thick rope. The point where the two ropes are attached is the boundary. At this point, a wave pulse will transfer from one medium to another. What will happen here?

47. 46 Change in Medium In this situation part of the wave is reflected, and part of the wave is transmitted. Part of the wave energy is transferred to the more dense medium, and part is reflected. The transmitted pulse is upright, while the reflected pulse is inverted.

48. 47 Change in Medium The speed and wavelength of the reflected wave remain the same, but the amplitude decreases. The speed, wavelength, and amplitude of the transmitted pulse are all smaller than in the incident pulse.

49. 48 Change in Medium Animation Test your understanding

50. Standing Waves standing wave patterns are produced as the result of the repeated interference of two waves of identical frequency while moving in opposite directions along the same medium. All standing wave patterns consist of nodes and antinodes continued

51. Basic info. The frequency associated with each harmonic is dependent upon the speed at which waves move through the medium and the wavelength of the medium. The speed at which waves move through a medium is dependent upon the properties of the medium (tension of the string, thickness of the string, material composition of the string, etc.). The wavelength of the harmonic is dependent upon the length of the string and the harmonic number (first, second, third, etc.).

52. Standing Wave 1 st Harmonics 2 nd Harmonics

53. Standing Wave 3 rd Harmonic 4 th Harmonic

54. 53 Wave Interaction All we have left to discover is how waves interact with each other. When two waves meet while traveling along the same medium it is called INTERFERENCE.

55. Interference the result of the superposition of two or more waves Superposition Principle the displacement of the medium when two or more waves pass through it at the same time and is the algebraic sum of the displacements caused by the individual waves

56. Interactions of waves: INTERFERENCE: when two or more waves arrive at the same point and at the same time they interact with each other. They will combine in 2 different ways.

57. Constructive larger amplitude results in a larger amplitude Types of Interference Destructive smaller amplitude results in a smaller amplitude

58. Constructive larger amplitude results in a larger amplitude

59. Destructive smaller amplitude results in a smaller amplitude

60. Interference 1. Constructive interference: crest of one wave meets the crest of another wave. You then add together to form a single wave.

61. Interference 2. Destructive interference: when the crest of one wave meets a trough of another wave, they combine by subtracting from each other to form a single wave.

62. Interactions of waves: There are 3 basic wave interactions: 1. REFLECTION: Bouncing back of a wave after it strikes a boundary that doesn’t absorb the wave’s energy.

63. Law of Reflection States the angle of incidence is equal to the angle of reflection. Angle of incidenceAngle of Reflection Reflected wave – the wave coming out Incident Wave – The wave coming in

64. Interactions of waves: 2. REFRACTION: remember waves do NOT bend as they travel through a medium they travel in a straight line. But if they travel through DIFFERENT mediums (air-water) or (glass-air), they bend.

65. Refraction: They bend because the speed of the wave changes as they travel through different mediums.

66. Interactions of waves: 3. DIFFRACTION : bending of waves around the edge of a barrier. New waves forming after the original strikes the barrier.

67. Diffraction Example: Think of the Macy’s parade, you will hear the marching band way before you can see them.

68. Causing another object to vibrate without contact by matching the natural frequency An opera singer can shatter a glass if the singer’s voice matches the natural frequency of the glass http://www.youtube.com/watch?v=m686UO68AXI

70. Practice Questions Light shines through a keyhole on a door. John notices that the shadow shape on the wall is much larger and fuzzier than the real keyhole outline. This is due to – A.refraction B.diffraction C.resonance D.reflection

71. Practice Questions One tuning fork is struck and placed next to an identical fork. The two forks do not touch. The second tuning fork starts to vibrate because of – A.interference B.the Doppler effect C.resonance D.standing waves

72. Practice Questions Diverging lenses are useful to people who suffer from nearsightedness because the lenses can cause images of distant objects to be focused on the retina. Lenses allow images to be focused on the retina because of — F diffusion G reflection H diffraction J refraction

73. Practice Questions When a DVD is read, laser light touches the DVD surface and is then measured at location A. What allows light to return to location A after striking the DVD surface? F Conduction G Refraction H Magnification J Reflection

74. Practice Questions In the drawing to the right, the straw is actually in one piece, but appears to be in two pieces. How would you explain this phenomenon to your friends? A.) The liquid absorbs the light and reflects only certain colors B.) The liquid polarizes the light rays and causes some of them to be blocked C.) The liquid reflects the image from inside the glass D.) The liquid refracts the light rays by changing their speed and angle

75. Practice Questions An empty cup was tightly covered with plastic wrap, and a few grains of salt were sprinkled on top of the plastic. When a tuning fork was struck and placed slightly above the plastic wrap, the salt began to move. Which characteristic of waves does the movement of the salt best demonstrate? A Echo formation B Diffraction C Resonance D Specular reflection

76. Practice Questions The diagram shows waves approaching a barrier. Which pattern will form after the waves pass through the opening in the barrier?

77. Practice Questions An individual stands in the bottom of a canyon and yells. The sound echos back to the person. This is an example of: F Reflection G Refraction H Diffraction J Resonance

78. Practice Questions A guitar player is seated next to a piano. The piano player strikes an E key on the piano. The guitarist reports that this causes the E string on his guitar to vibrate. What is the name of this phenomenon? A Polarization B Resonance C Reflection D Diffraction

79. Waves are everywhere in nature Sound waves, visible light waves, radio waves, microwaves, water waves, sine waves, telephone chord waves, stadium waves, earthquake waves, waves on a string, slinky waves

80. Waves Objectives 1. Recognize a wave in nature or technology. 2. Measure or calculate the wavelength, frequency, amplitude, and speed of a wave. 3. Give examples of transverse and longitudinal waves. 4. Give at least one example of reflection, refraction, absorption, interference, and diffraction. 5. Describe how boundaries create change in waves.