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Chapter Twenty-Three: Waves

Chapter Twenty-Three: Waves. 23.1 Harmonic Motion 23.2 Properties of Waves 23.3 Wave Motion. 1. 23.1 Harmonic motion. Linear motion gets us from one place to another. Harmonic motion is motion that repeats over and over. 2. Harmonic motion.

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Chapter Twenty-Three: Waves

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  1. Chapter Twenty-Three: Waves • 23.1 Harmonic Motion • 23.2 Properties of Waves • 23.3 Wave Motion 1

  2. 23.1 Harmonic motion • Linear motion gets us from one place to another. • Harmonic motion is motion that repeats over and over. 2

  3. Harmonic motion • A pendulum is a device that swings back and force. • A cycle is one unit of harmonic motion. 3

  4. Oscillators • An oscillatoris a physical system that has repeating cycles or harmonic motion. • Systems that oscillate move back and forth around a center or equilibrium position. 4

  5. Oscillators • A restoring force is any force that always acts to pull a system back toward equilibrium.

  6. Harmonic motion • Harmonic motion can be fast or slow, but speed constantly changes during its cycle. • We use period and frequency to describe how quickly cycles repeat themselves. • The time for one cycle to occur is called a period. 6

  7. Harmonic motion • The frequencyis the number of complete cycles per second. • Frequency and period are inversely related. • One cycle per second is called a hertz, abbreviated (Hz). 7

  8. Solving Problems • The period of an oscillator is 2 minutes. • What is the frequency of this oscillator in hertz? 9

  9. Solving Problems • Looking for: frequency in hertz • Given: period = 2 min • Relationships: • 60 s = 1 min • f = 1/T • Solution: f = 1/120 s f = .008 Hz 10

  10. Amplitude • Amplitude describes the “size” of a cycle. • The amplitude is the maximum distance the oscillator moves away from its equilibriumposition. 11

  11. Amplitude • The amplitude of a water wave is found by measuring the distance between the highest and lowestpoints on the wave. • The amplitude is half this distance. 12

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  13. Amplitude • Example: A pendulum with an amplitude of 20 degrees swings 20 degrees away from the center in either direction. 14

  14. Graphs of harmonic motion • A graph is a good way to show harmonic motion because you can quickly recognize cycles. • Graphs of linear motion do not show cycles. 15

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  16. A wave with an amplitude of 2cm and a period of 1 second. 4 3 2 1 0 1 2 3 4 0 1 2 3

  17. Exit Card: • Label the parts of the transverse wave. • Crest • Trough • Wavelength • Amplitude

  18. Chapter Twenty-Three: Waves • 23.1 Harmonic Motion • 23.2 Properties of Waves • 23.3 Wave Motion 19

  19. 23.2 Waves • A wave is an oscillation that travels from one place to another. • If you poke a floating ball, it oscillates up and down. • The oscillation spreads outward from where it started.

  20. What Are Mechanical Waves? • A wave is a disturbance that travels through matter or empty space. • Waves transfer energy.  • Some waves travel through matter called a medium. • Waves are caused by vibrations.

  21. Vibrations and Waves • All waves are the propagation of vibrations. • Without a vibration there would be no sound. • No light. • No TV. • No radio.

  22. What does propagation of vibrations mean?

  23. Waves • When you drop a ball into water, some of the water is pushed aside and raised by the ball.

  24. Waves • Waves are a traveling form of energy because they can change motion. • Waves also carry information, such as sound, pictures, or even numbers.

  25. Frequency, amplitude, and wavelength • You can think of a wave as a moving series of high points and low points. • A crest is the high point of the wave. • A trough is the low point.

  26. Frequency • The frequency of a wave is the rate at which every point on the wave moves up and down. • Frequency means “how often”.

  27. Amplitude • The amplitude of a water wave is the maximum height the wave rises above the level surface.

  28. Wavelength • Wavelength is the distancefrom any point on a wave to the same point on the next cycle of the wave. • The distance between one crest and the next crest is a wavelength.

  29. Bell Work • Answer Questions 1-4

  30. A wave with an amplitude of 1cm and a wavelength of 2 cm. 2 1.5 1 .5 0 .5 1 1.5 2 0 1 2 3 4 5 6 7 8 9

  31. A wave with an amplitude of 1.5cm and a wavelength of 3 cm. 2 1.5 1 .5 0 .5 1 1.5 2 0 1 2 3 4 5 6 7 8 9

  32. The speed of waves • The speed of a water wave is how fast the wave spreads, NOT how fast the water surface moves up and down or how fast the dropped ball moves in the water. How do we measure the wave speed?

  33. The speed of waves • A wave moves onewavelength in each cycle. • Since a cycle takes one period, the speed of the wave is the wavelength divided by the period.

  34. The speed of waves • The speed is the distance traveled(one wavelength) divided by the timeit takes (one period). • We usually calculate the speed of a wave by multiplying wavelength by frequency.

  35. Wave Speed (Velocity) V=l f • The Greek letter l iswavelength.

  36. Solving Problems • The wavelength of a wave on a string is 1 meter and its speed is 5 m/s. • Calculate the frequency and the period of the wave.

  37. Solving Problems • Looking for: • frequency in hertz • period in seconds • Given •  = 1 m; s = 5 m/s • Relationships: • s = f x  or f = s ÷  • f = 1/Tor T = 1/f • Solution • f = 5 m/s ÷1 m = 5 cycles/s • T = 1/5 cycles/s = .2 s f = 5 Hz T = 0.2 s

  38. A wave in a spring has a wavelength of 1 meters and a period of 2 seconds. What is the speed of the wave? • Speed = wavelength / period • S = 1 m/ 2 s • S= 0.5 m/s

  39. What is the speed of an ocean wave that has a wavelength of 4.0 m and a frequency of 0.5 hz? • Speed = wavelength x frequency • Speed = 4.0 m x 0.5 hz • Speed = 2 m/s

  40. Find the wavelength of a wave in a rope that has a frequency of 20 hz and a speed of 4 m/s. • Wavelength = speed / frequency • Wavelength = 4 m/s / 20 hz • Wavelength = 0.2 m

  41. A wave with an amplitude of 3cm and a wavelength of 6 cm. 4 3 2 1 0 1 2 3 4 0 1 2 3 4 5 6 7 8 9

  42. A wave with an amplitude of 4cm and a wavelength of 4 cm. 4 3 2 1 0 1 2 3 4 0 1 2 3 4 5 6 7 8 9

  43. Chapter Twenty-Three: Waves • 23.1 Harmonic Motion • 23.2 Properties of Waves • 23.3 Wave Motion

  44. 23.3 Wave Motion • A wave front is the leading edge of a moving wave which is considered to be the crest for purposes of modeling. • The crests of a planewave look like parallel lines. • The crests of a circularwave are circles.

  45. Four wave interactions • When a wave encounters a surface, four interactions can occur: • reflection, • refraction, • diffraction, • absorption.

  46. Wave interactions • A boundaryis an edge or surface where things change. • Reflection, refraction, and diffraction usually occur at boundaries.

  47. Reflection • Reflection: Bouncing off a barrier. • Law of Reflection- Where the angle of incidence equals the angle of reflection.

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