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CHAPTER 15 : CHARACTERISTICS OF WAVES

CHAPTER 15 : CHARACTERISTICS OF WAVES. What are Waves ?. Wave = a disturbance that transfers energy from place to place. Remember, energy = the ability to do work!. The disturbance caused by a wave is only temporary. What carries Waves?.

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CHAPTER 15 : CHARACTERISTICS OF WAVES

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  1. CHAPTER 15 : CHARACTERISTICS OF WAVES

  2. What are Waves? • Wave = a disturbance that transfers energy from place to place. • Remember, energy = the ability to do work!

  3. The disturbance caused by a wave is only temporary.

  4. What carries Waves? • Medium = the material through which a wave travels. • Gases, liquids, & solids all act as mediums

  5. Mechanical waves = waves that require a medium through which to travel. • -Waves do not carry the medium itself with them. • Waves travel through the water but don’t carry the water with them. How does the duck show this?

  6. What Causes Waves? • Waves are created when a source of energy causes a medium to vibrate. • Vibration = a repeated back and forth or up-down motion. • The motion is the source of the wave!

  7. What is the source of vibrations in this picture?

  8. A moving object has energy. The moving object can transfer energy to a nearby medium, creating a wave. • Ex: As propellers of a boat turn, they disturb the calm water surface. The boat’s propellers transfer energy to the water. The propeller produces a wave that travels throughout the water. As the boat moves through the water, it also causes waves.

  9. What might have caused this disturbance? What is the medium?

  10. Types of Waves • Waves are classified by how they move. The 3 types are: • Transverse • Longitudinal • Surface

  11. Transverse Waves • Transverse Waves = waves that move the medium at right angles to the direction in which the waves are traveling (Ex. The wave on a rope). • As a transverse wave moves in one direction, the particles of the medium move across the direction of the wave.

  12. Direction of wave The highest parts of the wave are crests. The lowest parts are troughs.

  13. Longitudinal Waves • Longitudinal waves move the particles of the medium parallel to the direction that the waves are traveling (Ex. Coils in a Slinky). • Compressions = the parts where the coils are close together. • Rarefractions = the parts where the coils are spread out, or rarefied.

  14. As compressions & rarefactions travel along the Slinky, each coil moves slightly forward and then back.

  15. The energy travels from one end of the Slinky to the other, creating a wave. • After the wave passes, each part of the spring returns to the position where it started.

  16. Combinations of Waves • Surface waves are combinations of transverse & longitudinal waves. • Occur at the surface between 2 mediums, such as water & air.

  17. When waves pass through water, the water (& anything on it) moves up & down, like a transverse wave.

  18. Surface waves • The water also moves back & forth slightly in the direction that the wave is traveling, like the coils of the Slinky. • But unlike the Slinky, water does not compress.

  19. The up-and-down & back-and-forth movements combine to make each particle of water move in a circle.

  20. How would waves affect the motion of a ship?

  21. Properties of WavesSection 15 - 2 • Basic properties of waves: • amplitude • wavelength • frequency • speed

  22. Amplitude • Is the maximum distance the particles of the medium carrying the wave move away from their rest positions. • A measurement of how much a particle in the medium is disturbed by the wave.

  23. Amplitude of a Transverse Wave

  24. Amplitude of longitudinal waves - very crowded = large amplitude

  25. Amplitude is theLOUDNESS of a sound wave.

  26. Wavelength • The distance a wave travels before it starts to repeat. • The distance between 2 corresponding parts of a wave.

  27. Transverse Wave Longitudinal Wave The crest of a transverse wave is similar to the compression of a longitudinal wave. Trough/rarefaction

  28. Two characteristics of waves - wavelength & amplitude.

  29. Frequency • The number of complete waves that pass a given point in a certain amount of time. • Or the number of vibrations per second. • Measured in Hertz (Hz) • 1 wave or vibration / second = 1Hz

  30. Which set of waves would have the greatest frequency?

  31. We hear the frequency of sound waves as pitch. LOW PITCH MEDIUM PITCH HIGH PITCH

  32. SPEED • Different waves travel at different speeds. • Speed, wavelength & frequency • are related to each other by a mathematical formula. • Speed - wavelength x frequency

  33. Speed = wavelength x frequency Frequency = speed / wavelength wavelength = speed / frequency

  34. Speed of different types of waves • Light travels faster than sound • - Thunder & lightning

  35. Speed in different mediums • Waves in different mediums travel at different speeds. • Sound waves traveling through air at the same pressure & temperature, travel at the same speed. • But if the temp or pressure change, the speed of waves change also.

  36. Speed & change of frequency • If you increase frequency then wavelength must decrease. Freq. Increase

  37. Sec. 3: Interactions of Waves • There are 5 main types of interactions of waves: • Reflection, • Refraction, • Diffraction, • Interference, & • Standing waves

  38. Reflection • Reflection = when an object or wave hits a surface through which it cannot pass, it bounces back. • Ex: • Ball that hits a wall & bounces back • Echoes are reflected sound

  39. Draw this diagram in your notes!

  40. Angle of Incidence = the angle between the incoming wave & the imaginary perpendicular line. • Angle of Reflection = the angle between the reflected wave & the imaginary line.

  41. Law of Reflection • Law of Reflection states that the angle of reflection equals s the angle of incidence. • All waves obey the law of reflection.

  42. Refraction • When a wave moves from one medium into another medium at an angle, it changes speed as it enters the second medium, which causes it to bend. • The bending of waves due to a change in speed is called refraction.

  43. All waves change speed when entering a new medium, they don’t always bend. • Bending occurs when one side of the wave enters the new medium before the other side of the wave. The side that enters 1st changes speed first. The other side is still traveling at its original speed. • Bending occurs because the 2 sides of the wave are traveling at different speeds.

  44. Have you every pushed a shopping cart that had a very stiff wheel? • Was it easy to push? • Was it easy to control the direction of the cart? • How is this example related to refraction?

  45. Diffraction • When a wave passes a barrier or moves through a hole in a barrier, it bends and spreads out. • Diffraction = the bending of waves around the edge of a barrier.

  46. A wave can go through a hole in a barrier & spread out

  47. Or, a wave can bend around a corner.

  48. Interference • When 2 or more waves meet, they have an effect on each other. This interaction is called interference. • 2 types of interference: • Constructive • Destructive

  49. Constructive Interference • Occurs whenever 2 waves combine to make a wave with a larger amplitude. • Waves “helping each other” to give a stronger result, adding energy

  50. Notice how the crests & troughs are aligned. This allows them to “add” together.

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