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Chapter 17

Chapter 17. Mechanical Waves & Sound. How does a disturbance produce waves?. Procedure Fill a clear plastic container with water.

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Chapter 17

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  1. Chapter 17 Mechanical Waves & Sound

  2. How does a disturbance produce waves? • Procedure • Fill a clear plastic container with water. • Observe the surface of the water by looking down at an angle to the container. Use the pipet to release a drop of water from a height of 3 cm above the surface of the water. • Repeat Step 2 with a drop released from each of these heights: 10, 20, 50, 60, 70, 90 cm. Create a table to record your observations after each drop. • These observations will be QUALITATIVE (or descriptive, and not mumeric)

  3. Analysis Questions • Which drop produced the highest wave? • Write a general statement (or conclusion) about how the distance a drop falls affects the wave produced in the container. • Using your knowledge of energy, conservation of energy, and energy transfer, explain why the distance a drop falls affects the height of the wave produced. Thoroughly explain your answer.

  4. Mechanical Waves 17.1 Notes

  5. Inquiry Activity • How does a disturbance produce waves? • P 499 • Complete activity, answer questions as a group • Submit one paper per group with all observations recorded and questions answered!

  6. What are mechanical waves? • Mechanical Wave • A disturbance in matter that carries energy from one place to another • Require a medium (or matter) in order to carry energy • All waves carry energy!

  7. What is a Medium? • The material through which a wave travels • Can be a solid, a liquid or a gas • Space is NOT a medium • Why?

  8. How are mechanical waves created? • A source of energy causes a vibration to travel through a medium

  9. Types of Mechanical Waves Transverse Longitudinal (Compressional) Medium moves parallel to the direction the wave travels • Medium moves perpendicularly (or at right angles to the direction the wave travels)

  10. Transverse Waves Demos • Rope (with ribbon attached) • Student line (arms over shoulders)

  11. Parts of a Transverse Wave Crest Trough Lowest point of the wave • Highest point of the wave

  12. Compressional Wave Demos • Slinkys! • Hip Bump

  13. Parts of a Compressional Wave Compression Rarefaction An area where the particles in a medium are spread out • Area where the particles in a medium are spaced close together

  14. Waves transfer ENERGY! • Waves DO NOT transfer MATTER • Waves ONLY transfer ENERGY • Example: THE HUMAN WAVE

  15. Surface Waves • A wave that travels along a surface that separates two media (or two types of matter) • An object resting on a surface wave will move up and down, and back and forth • These two motions result in a circular motion for the object

  16. Wave Animation • http://njscuba.net/biology/misc_waves_weather.html

  17. Breaking Waves

  18. Exit Exercise • With your group, make a Venn Diagram that compares and contrast Transverse and Compressional Waves.

  19. Properties of Mechanical Waves 17.2

  20. Periodic Motion • Any motion that repeats at regular time intervals • Period • The time required for one cycle, a complete motion that returns to its starting point

  21. Wavelength • Distance between a point on one wave and the same point on the next cycle of the wave • Between adjacent Crests (or troughs), or compressions (or rarefactions)

  22. One complete wave cycle One Wavelength

  23. Frequency • A periodic motion has a frequency • Frequency • The number of complete cycles in a given time • For waves, this is the number of wave cycles that pass a point in a given time • Measured in cycles per second, or Hertz (Hz)

  24. Frequency & Wavelength • As frequency increases, what happens to wavelength? • Use the slinky at your table to determine the answer to this question, then respond using Socrative • HINT: You can make either TRANSVERSE, or COMPRESSIONAL waves with your slinky

  25. Frequency Formula Frequency = 1 *Remember, period is the amount of time it takes for a wave to complete one full cycle period

  26. Socrative Graph #1

  27. Socrative Graph #2 t in seconds

  28. Socrative Questions… • Two calculating frequency/ period questions

  29. Surfing • Science of Surf - Episode 1

  30. Wave Speed • REMEMBER • v = d/t • Think of one wavelength as DISTANCE • Think of period as TIME • Wave Speed = wavelength / period • OR Wave Speed = wavelength x frequency

  31. Wave Speed Example • One end of a rope is vibrated to produce a wave with a wavelength of 0.25 meters. The frequency of the wave is 3.0 Hertz. What is the speed of the wave? • FORMULA • Speed = Wavelength x Frequency

  32. Socrative Practice • Wave Speed Questions

  33. Amplitude • The maximum displacement of the medium from its rest position • The more energy a wave has, the greater its amplitude

  34. Behavior of Waves 17.3

  35. Reflection • Occurs when a wave bounces off a surface that it cannot pass through • Does not change wave speed or frequency, but does change wave direction

  36. Refraction • Bending of a wave as it enters a new medium • Occurs because one side of the wave moves more slowly than the other side

  37. Refraction Example • Pencil in water demonstration

  38. Diffraction • Bending of a wave as it moves around an obstacle or passes through a narrow opening • A wave diffracts more if its wavelength is large compared to the size of an opening or obstacle

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