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WAVES

WAVES. Chapter 15. Objectives. Explain how forces cause waves. Explain how waves transfer energy. Classify wave types. Compare and contrast different wave types in an experiment. A wave is a disturbance.

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WAVES

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  1. WAVES Chapter 15

  2. Objectives • Explain how forces cause waves. • Explain how waves transfer energy. • Classify wave types. • Compare and contrast different wave types in an experiment.

  3. A wave is a disturbance • You experience waves everyday. Every sound you hear is a sound wave, every sight you see depends on light waves!

  4. Check out this Wave... • A Wave is a disturbance that transfers energy from one place to another. • Waves can transfer energy over distance without moving matter the entire distance. • For example: An ocean wave can travel many kilometers without the water itself moving many kilometers. • Water moves up and down

  5. Forces & Waves • Forces can start a disturbance, sending a wave through a material. Rope Wave Water Wave

  6. Earthquake Waves

  7. Materials and Waves • A rope tied to a doorknob, water, and the ground all have something in common. • They are all materials through which waves move. • A medium is any substance that a wave moves through. Like water or a rope

  8. Mechanical Waves • Waves that transfer energy through matter are known as mechanical waves. • All the waves you’ve learned about so far are mechanical waves. • An Earthquake wave is a good example of energy transfer.

  9. Types of Waves • Waves can be classified by how they move! • Some waves transfer an up-and-down or a side-to-side motion.

  10. Transverse Waves Transverse Wave direction of disturbance direction of wave transfer of energy http://www.cbu.edu/~jvarrian/applets/waves1/lontra_g.htm

  11. Longitudinal Wave direction of disturbance direction of wave transfer ofenergy Longitudinal Waves

  12. Earthquakes • Earthquakes are capable of producing both transverse and longitudinal waves which travel through the solid structures of the Earth. When seismologists began to study earthquake waves they noticed that only longitudinal waves were capable of traveling through the core of the Earth. For this reason, geologists believe that the Earth's core consists of a liquid - most likely molten. The speed of a wave is determined by the medium carrying the wave.

  13. Let's Try to Do ~THE WAVE~

  14. 15.2 Properties of Waves • Learn how to measure amplitude, wavelength, and frequency. • Calculate a waves speed • Collect data to investigate how to change frequency in an experiment.

  15. How can Waves be Measured? • Height • Speed • Lengths • Also known as: • Amplitude • Wavelength • Frequency

  16. Measuring Wave Properties • A crest is the highest point, or peak, of a wave. • A trough is the lowest point, or valley, of a wave

  17. crest water level at rest fixed point trough • E:\Animations\wslm05_pg18_graph.html

  18. Amplitude • Amplitude for a transverse wave is the distance between a line through the middle of a wave and a crest or trough. • Amplitude is an important measurement because it indicates how much energy a wave is carrying.

  19. Wavelength • The distance from one wave crest to the next crest is called the wavelength. • Can also be measured from trough to trough.

  20. Wavelengths

  21. Frequency • The number of waves passing a fixed point in a certain amount of time is called the frequency. • It measures how often a wave occurs. • Frequency Animation

  22. How Frequency and Wavelength are Related • When frequency increases more wave crests pass a fixed point each second. That means the wavelength shortens. • So, as frequency increases, wavelength decreases. • The opposite is also true. • Look at picture on page 498

  23. Graphing Wave Properties • The graph of a transverse wave looks like a wave itself • The graph of a longitudinal wave looks like a spring of coils. • Page 499

  24. Measure Wave Speed • The speed of any wave can be determined when both the frequency and the wavelength are known, using this formula: • Speed= wavelength * frequency • S= λ f • Look at the example on page 501

  25. Waves Travel • Different types of waves can travel at very different speeds. • Light waves travel through air almost a million times faster than sound. • Example: Thunder and Lightening

  26. Try This • In a stormy sea, 2 waves pass a fixed point every second, and the waves are 10 m apart. What is the speed of the waves? • S= λ f • S= 10 m/wave * 2 wave/s • = 20m/s

  27. Review • What two measurements of a wave do you need to calculate its speed? • What is the top of a wave called? Bottom? • What does the “Frequency” of a wave mean ?

  28. 15.3 Waves Behave in Predictable Ways • Describe how waves change as they encounter a barrier. • Explain what happens when waves enter a new medium. • Identify ways in which waves interact with one another.

  29. Waves interact with materials • When waves interact with materials, they behave predictably. • Scientist call these behaviors: Reflection, Refraction, and Diffraction.

  30. Reflection • The bouncing back of a wave after it strikes a barrier is called reflection. • Water, sound & light waves all reflect.

  31. Refraction • Sometimes, a wave does not bounce back when it encounters a new medium. • Refraction is the bending of a wave as it enters a new medium at an angle other than 90 degrees.

  32. Diffraction • You have seen how waves reflect off a barrier. For example, water waves bounce off the side of a pool. But what if the side of the pool had an opening in it? • Diffraction is the spreading out of waves through an opening or around the edge of an obstacle. • Occurs in all types of waves.

  33. Diffraction • Sound waves diffract as they pass through an open doorway. • Turn on a TV and then walk into another room. You can still hear it because the waves spread out.

  34. Waves Interact with Other Waves • Interference is the meeting and combining of waves. • The adding of two waves is called constructive interference. It builds up, or constructs, a larger wave out of two smaller ones. Page 507 • Destructive Interference is when one wave attaches briefly to the trough of another wave. The energy of one wave is subtracted from the energy of the other. Page 508

  35. Review • Explain what happens when waves encounter a medium that they cannot travel through? • Describe a situation in which waves would diffract. • Describe two ways that waves are affected by interference.

  36. TEST NEXT MONDAY, STUDY!!!

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