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Understanding Mechanical Waves: How Disturbances Create Wave Patterns

This chapter explores mechanical waves, detailing how disturbances in matter produce wave patterns that carry energy. Through an engaging hands-on experiment, participants release water drops from varying heights, observing qualitative changes in wave behavior. Key concepts include the characteristics of mechanical waves, the distinction between transverse and compressional waves, and the roles of mediums. The chapter emphasizes the principles of energy transfer, period, frequency, and wave speed while facilitating group discussions and Venn diagram comparisons to deepen understanding of wave properties.

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Understanding Mechanical Waves: How Disturbances Create Wave Patterns

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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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