Chapter 10 Waves

1. Chapter 10 Waves

2. Hmmmm . . . • What do you think of when you hear the word wave? • Write a brief description in yourcomposition book of what you think a wave is. • Then write a short paragraph describing a time you might have experienced waves.

3. Section 1: The Nature of Waves

4. Objectives (things you just might learn) • Describe how vibrations in materials set up wave disturbances that spread away from the source. • Distinguish between waves that require a medium and waves that do not. • Explain the difference between transverse and longitudinal waves.

5. Waves and Energy • A wave is any disturbance that transmits energy through matter or empty space. • The energy passed along by a wave moves farther and farther from the source of energy. • Energy can be carried away from its source by a wave. However, the material through which the wave travels does not move with the energy.

7. Waves and Energy, continued • Vibrations and Waves A repetitive, back-and-forth motion of an object is called a vibration. • Vibrations set up wave disturbances in a material, and the waves spread away from the source of vibration. • A vibrating particle passes its energy to a nearby particle. In this way, energy is transmitted through a material.

8. Waves and Energy, continued • Energy Transfer Through a Medium Most waves transfer energy by the vibration of particles in a medium. A mediumis matter through which a wave can travel. • These are called “mechanical waves.” • Sound waves, water waves, and seismic waves all need a medium through which to travel.

9. Wave Energy, continued • Energy Transfer Without a Medium Visible light waves, microwaves, radio waves, and X rays are examples of waves can transfer energy without going through a medium. • These waves are electromagnetic waves. Although electromagnetic waves do not need a medium, they can go through matter.

10. TRANSVERSE WAVES • Transverse Waves are waves in which the particles vibrate perpendicularly to the direction the wave is traveling. • Transverse waves are made up of crests and troughs. • Water waves, waves on a rope, and electromagnetic waves are examples of transverse waves. • http://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html

11. Crests and Troughs of Transverse Waves • Transverse waves have alternating high points and low points. • The high point of a wave is a crest. • The low point of a wave is a trough.

12. COMPRESSION WAVES • Compression Waves are waves in which the particles vibrate back and forth along the path that the waves moves. • Compression waves are also known as longitudinal waves. • Compression/longitudinal waves are made up of compressionsand rarefactions. • Waves on a spring are longitudinal waves. • http://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html

13. Rarefactions and Compressions of Longitudinal/Compression Waves • Longitudinal waves do not have crests and troughs. • The region where the particles of matter are crowded together as the wave of energy moves through is called a compression. • The region where the particles are spread out as the wave moves through is called a rarefaction. • http://www.absorblearning.com/media/attachment.action?quick=14w&att=2933

15. SOUND WAVES • Sound Waves are longitudinal waves. Sound waves travel by compressions and rarefactions of air particles, as shown below.

16. SURFACE WAVES • Surface Waves: Combinations of Waves A transverse waves and a longitudinal wave can combine to form a surface wave. • Surface waves look like transverse waves, but the particles of the medium move in circles rather than up and down.

18. SEISMIC WAVES • Seismic waves are caused by earthquakes. • Energy is released when crust breaks. • Seismic waves occur as both transverse and compressional waves. • Primary waves are compressional and travel fastest. They can travel through solids and liquids. • Secondary waves are transverse and travel more slowly due to the way they move. They cannot travel through liquids—like Earth’s liquid outer core. • Surface waves (Love and Rayleigh) are both transverse and compressional. They move in all directions and cause the most damage.

19. Section 2: Wave Properties Hmmmmm . . . Draw a longitudinal wave and a transverse wave in yourcomposition book.Label the parts of each wave.

20. Objectives: What you should learn . . . • Identify and describe four wave properties. • Explain how frequency and wavelength are related to the speed of a wave.

21. Amplitude • The amplitudeof a wave is the maximum distance that the particles of a medium vibrate from their rest position. • A wave with a large amplitude carries more energy than a wave with a small amplitude does.

22. WAVELENGTH • A wavelengthis the distance between any point on a wave to an identical point on the next wave. • A wave with a shorter wavelength carries more energy than a wave with a longer wavelength does.

23. FREQUENCY • Frequencyis the number of waves produced in a given amount of time. • Frequency can be found by counting the number of crests or troughs that pass a point each second. • Frequency is usually expressed in hertz (Hz). One hertz equals one wave per second. • High frequency means more waves per second. • Low frequency means fewer waves per second. • If the amplitudes (wave heights) are equal, high-frequency waves carry more energy than low-frequency waves.

24. HERTZ • A frequency of 1 Hz means that 1 wavelength passes a point in one second. 5 Hz means that 5 waves pass a point in one second. • As frequency increases, wavelength decreases. In other words, the more waves that go by per second, the distance between them decreases.

26. WAVE SPEED • Wave Speedis the speed at which a wave travels. • The speed depends on the medium a wave travels through. • Waves usually travel faster in liquids and solids than they do in gases. • An exception is light waves, which travel through empty space fastest, and gases next fastest. • Sounds waves travel faster in a medium if the temperature is increased.

27. More on WAVE SPEED • Wave speed (v) can be calculated using wavelength () and frequency (f), by using the wave equation, which is shown below: • v    f • (Speed = frequency x wavelength)

28. WAVE Period • The amount of time it takes for one wavelength to pass a point is the wave’s period. • http://www.lajollasurf.org/nepap.html

30. How Ocean Waves Work http://oceanexplorer.noaa.gov/edu/learning/9_ocean_waves/activities/breaking_waves.html Deadliest Catch Physics of Waves: http://www.youtube.com/watch?v=edOUDbFtFk0&feature=related

31. Amplitude of Compressional Waves • In higher amplitude of a compressional/longitudinal wave, the particles of a compression are closer, and particles in the rarefaction are farther apart. • In lower amplitude, the particles in compression are farther apart, and rarefaction particles are closer together

32. More on Compressional Waves Animation of above compressional wave: http://www.passmyexams.co.uk/GCSE/physics/basic-waves-theory.html

33. Section 3: The Behavior of Waves Hmmmmmm….. Write the symbols v, f, and  in yourcomp book. What does each symbol stand for? How does each symbol relate to the other two symbols? Draw a diagram if it helps.

34. Objectives • Describe reflection, diffraction, and interference. • Explain how different media affect wave speed and cause refraction. • Compare destructive interference with constructive interference. • Describe resonance, and give examples.

35. Reflection • Reflectionhappens when a wave bounces back after hitting a barrier. • Light waves reflecting off an object allow you to see that object. A reflected sound wave is called an echo. • Waves are not always reflected when they hit a barrier. A wave is transmitted through a substance when it passes through the substance.

36. Law of Reflection • According to the law of reflection, the angle of incidence is equal to the angle of reflection. • “Incidence” refers to where the wave comes in contact with a surface. • http://www.teachersdomain.org/asset/lsps07_vid_lightreflect/

37. Refraction • Refractionis the bending of a wave as the wave pass from one medium to another at an angle. • http://www.teachersdomain.org/asset/rr10_vid_refrac/ • When a wave moves from one medium to another, the wave’s speed and wavelength changes. As a result, the wave bends and travels in a new direction. • When light waves travel from air to water, they slow down and bend toward the perpendicular of the surface (normal).

39. Diffraction • Diffractionis the bending of waves around a barrier or through an opening. • The amount of diffraction of a wave depends on its wavelength and the size of the barrier or opening the wave encounters.

40. Diffraction • The smaller the wavelength compared to an obstacle the wave encounters, the less it diffracts. • Sound waves have a larger wavelength than light waves and, therefore, will diffract—or bend around doors and walls easier than light waves. • That’s why you can hear around corners, but do not see light as easily bend around a corner.

41. Diffraction of Radio Waves • Diffraction affects your radio’s reception. • AM radio waves have longer wavelengths than FM. • Longer wavelengths diffract (bend) around objects easier. • Therefore, AM has a tendency to be able to travel farther because obstacles do not get in their way as much.

42. Interference • Interferenceis the result of two or more waves overlapping. • Interference of sounds waves through a water medium. http://www.youtube.com/watch?v=aWZY3wwldjs&feature=related

43. Constructive Interference (in-phase) • Constructive Interferencehappens with the crests of one wave overlap with the crests of another wave or waves. The troughs of the waves also overlap. • In other words, the amplitudes (or energy) of the waves add together. • In sound waves, this increases loudness. • The result is a new wave that has a larger amplitude than the original waves had.

44. Destructive Interference (out-of-phase) • Destructive interferencehappens when the crests of one wave and the troughs of another wave overlap. The new wave have a smaller amplitude than the original waves had. • In other words, the waves subtract from one another to create a less energetic wave. • In sound waves, this causes a reduction in loudness. • When the waves involved in destructive interference have the same amplitude and meet each other at just the right time, the result is no wave at all (silence for sound waves).

46. Interference, continued • Standing Waves are waves that appear to be standing still. A standing wave only looks as if it is standing still. Waves are actually going in both directions. • In a standing wave, certain parts of the wave are always at the rest position because of total destructive interference. Other parts have a large amplitude because of constructive interference.

47. Chapter 10 Section3 Wave Interactions Interference, continued • The frequencies at which standing waves form are called resonant frequencies. • Resonance happens when an object vibrating at or near the resonant frequency of a second object causes the second object to vibrate. • http://www.science-animations.com/support-files/pendulum.swf • An example of resonance is shown on the next slide.

48. Chapter 10 Section3 Wave Interactions Interference, continued

50. General Information About Waves http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/waves/generalwavesrev1.shtml