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2. Resources Bellringers Chapter Presentation Transparencies Standardized Test Prep Image and Math Focus Bank CNN Videos Visual Concepts

3. The Energy of Waves Chapter 20 Table of Contents Section 1 The Nature of Waves Section 2 Properties of Waves Section 3 Wave Interactions

4. Chapter 20 Section1 The Nature of Waves Bellringer What do you think of when you hear the word wave? Write a brief description of what you think a wave is. Then, write a short paragraph describing a time you might have experienced waves.

5. Section1 The Nature of Waves Chapter 20 Objectives • Describe how waves transfer energy without transferring matter. • Distinguish between waves that require a medium and waves that do not. • Explain the difference between transverse and longitudinal waves.

6. Chapter 20 Section1 The Nature of Waves Wave Energy • A wave is any disturbance that transmits energy through matter or empty space. • 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. Chapter 20 Section1 The Nature of Waves

8. Chapter 20 Section1 The Nature of Waves Wave Energy, continued • Waves and Work As a wave travels, it does work on everything in its path. • The waves in a pond do work on the water to make it move up and down. The waves also do work on anything floating on the water’s surface. • The fact that the water and floating objects move tells you that the waves are transferring energy.

9. Chapter 20 Section1 The Nature of Waves Wave Energy, continued • Energy Transfer Through a Medium Most waves transfer energy by the vibration of particles in a medium. A medium is a substance through which a wave can travel. • Mechanical waves like sound waves, water waves, and seismic waves all need a medium through which to travel.

10. Chapter 20 Section1 The Nature of Waves Wave Energy, continued • Energy Transfer Without a Medium Electromagnetic waves like visible light waves, microwaves, radio waves, and X rays 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.

11. Chapter 20 Section1 The Nature of Waves Types of 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.

12. Chapter 20 Section1 The Nature of Waves Types of Waves, continued • Longitudinal Waves are waves in which the particles vibrate back and forth along the path that the waves moves. • Longitudinal waves are made up of compressions and rarefactions. • Waves on a spring are longitudinal waves.

13. Chapter 20 Section1 The Nature of Waves

14. Chapter 20 Section1 The Nature of Waves Types of Waves, continued • Sound Waves are longitudinal waves because they travel by compressions and rarefactions of air particles, as shown below.

15. Chapter 20 Section1 The Nature of Waves Types of Waves, continued • 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.

16. Chapter 20 Section2 Properties of Waves Bellringer Draw a longitudinal waveand label its compressions and rarefactions. Draw a transverse wave and label its crests and troughs.

17. Chapter 20 Section2 Properties of Waves Objectives • Identifyand describe four wave properties. • Relate wavelength, frequency, and amplitude to energy. • Explain how frequency and wavelength are related to the speed of a wave.

18. Chapter 20 Section2 Properties of Waves Amplitude • The amplitude of 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.

19. Chapter 20 Section2 Properties of Waves Wavelength • A wavelength is 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.

20. Chapter 20 Section2 Properties of Waves Frequency • Frequency is the number of waves produced in a given amount of time. Frequency is usually expressed in hertz (Hz). One hertz equals one wave per second. • If the amplitudes are equal, high-frequency waves carry more energy than low-frequency waves.

21. Chapter 20 Section2 Properties of Waves

22. Chapter 20 Section2 Properties of Waves Wave Speed • Wave Speed is the speed at which a wave travels. • Wave speed (v) can be calculated using wavelength () and frequency (f), by using the wave equation, which is shown below: • Wave speed (v) = wavelength () x frequency (f) • v    f

23. Chapter 20 Section2 Properties of Waves

24. Chapter 20 Section2 Properties of Waves Wave Speed, continued • Frequency and Wavelength RelationshipFrequency and wavelength are inversely related.So, if one value is doubled, the other value will be cut in half. • The wave speed of a wave in a certain medium is the same no matter what the wavelength is. So, the wavelength and frequency depend on the wave speed, not the other way around.

25. Chapter 20 Section2 Properties of Waves Characteristics of a Wave Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

26. Chapter 20 Section3 Wave Interactions Bellringer Write the following symbols and write what each symbol stands for V f 

27. Chapter 20 Section3 Wave Interactions Objectives • Describe reflection, refraction, diffraction, and interference. • Compare destructive interference with constructive interference. • Describe resonance, and give examples.

28. Chapter 20 Section3 Wave Interactions Reflection • Reflection happens when a wave bounces back after hitting a barrier. Ex.- moon • 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.

29. Chapter 20 Section3 Wave Interactions Refraction • Refraction is the bending of a wave as the wave pass from one medium to another at an angle. Ex. fishtank • 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.

30. Chapter 20 Section3 Wave Interactions Refraction, continued • Refraction of Different ColorsWhen light waves from the sun pass through a water droplet or a prism, the light is refracted. Ex. rainbow • But the different colors in sunlight are refracted by different amounts, so the light is spread out into its separate colors.

31. Chapter 20 Section3 Wave Interactions Diffraction • Diffraction is the bending of waves around a barrier or through an opening. Ex- music around a corner • The amount of diffraction of a wave depends on its wavelength and the size of the barrier or opening the wave encounters.

32. Chapter 20 Section3 Wave Interactions Interference • Interference is the result of two or more waves overlapping. • Constructive Interference happens with the crests of one wave overlap with the crests of another wave or waves. The troughs of the waves also overlap. • The result is a new wave that has a larger amplitude than the original waves had.

33. Chapter 20 Section3 Wave Interactions Interference, continued • Destructive Interference happens with the crests of one wave and the troughs of another wave overlap. The new wave have a smaller amplitude than the original waves had. • 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.

34. Chapter 20 Section3 Wave Interactions

35. Chapter 20 Section3 Wave Interactions 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.

36. Chapter 20 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. • An example of resonance is shown on the next slide.

37. Chapter 20 Section3 Wave Interactions Interference, continued

38. Chapter 20 The Energy of Waves Concept Map Use the terms below to complete the concept map on the next slide.

39. Chapter 20 The Energy of Waves

40. Chapter 20 The Energy of Waves

41. End of Chapter 20 Show

42. Standardized Test Preparation Chapter 20 Reading Read each of the passages. Then, answer the questions that follow each passage.

43. Standardized Test Preparation Chapter 20 Passage 1 On March 27, 1964, a powerful earthquake rocked Alaska. The earthquake started on land near Anchorage, and the seismic waves spread quickly in all directions. The earthquake created a series of ocean waves called tsunamisin the Gulf of Alaska. In the deep water of the gulf, the tsunamis were short and far apart. But as these waves entered the shallow water surrounding Kodiak Island, off the coast of Alaska, they became taller and closer together. Continued on the next slide

44. Standardized Test Preparation Chapter 20 Passage 1, continuedSome reached heights of nearly 30 m! The destructive forces of the earthquake and tsunamis killed 21 people and caused $10 million in damage to Kodiak, which made this marine disaster the worst in the town’s 200-year history.

45. Standardized Test Preparation Chapter 20 1. In the passage, what does tsunami mean? A a seismic wave B an earthquake C an ocean wave D a body of water

46. Standardized Test Preparation Chapter 20 1. In the passage, what does tsunami mean? A a seismic wave B an earthquake C an ocean wave D a body of water

47. Standardized Test Preparation Chapter 20 2. Which of these events happened first? FThe tsunamis became closer together. GTsunamis entered the shallow water. HTsunamis formed in the Gulf of Alaska. IAn earthquake began near Anchorage.

48. Standardized Test Preparation Chapter 20 2. Which of these events happened first? FThe tsunamis became closer together. GTsunamis entered the shallow water. HTsunamis formed in the Gulf of Alaska. I An earthquake began near Anchorage.

49. Standardized Test Preparation Chapter 20 3. Which conclusion is best supported by information given in the passage? AKodiak had never experienced a tsunami before 1964. BTsunamis and an earthquake were the cause of Kodiak’s worst marine disaster in 200 years. CTsunamis are common in Kodiak. DThe citizens of Kodiak went into debt after the 1964 earthquake.

50. Standardized Test Preparation Chapter 20 3. Which conclusion is best supported by information given in the passage? AKodiak had never experienced a tsunami before 1964. B Tsunamis and an earthquake were the cause of Kodiak’s worst marine disaster in 200 years. CTsunamis are common in Kodiak. DThe citizens of Kodiak went into debt after the 1964 earthquake.