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What are waves?

Waves. What are waves?. Wave. Definition : A disturbance that transfers energy from place to place. What carries waves? A medium , a medium is the material through which a wave travels. A medium can be a gas, liquid, or solid. Not all waves require a medium to travel.

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What are waves?

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  1. Waves What are waves?

  2. Wave • Definition: A disturbance that transfers energy from place to place. • What carries waves? A medium, a medium is the material through which a wave travels. • A medium can be a gas, liquid, or solid.

  3. Not all waves require a medium to travel. • Mechanical Waves are waves that require a medium. • Electromagnetic Waves travel through empty space and do not require a medium.

  4. What causes waves? • Waves are created when a source of energy causes a medium to vibrate. • A vibration is a repeated back and forth or up and down motion.

  5. How do waves carry energy? • Waves carry energy by displacement • The energy from this initial displacement causes the material nearby to also displace, which in turn displaces material near it... which creates a wave of energy propagating outwards. • It is important to note that the material may move around as the wave passes, but it is the energy which is propagating outwards, not the material itself.

  6. Lab: Slinkys in Action • Use a slinky to make different types of waves. • Notice how the ribbon moves with each different type of wave. • Where did the energy come from to start the wave? • How could you tell the wave carried energy?

  7. Types of waves: Waves are classified according to how they move.

  8. Transverse Wave • Teacher’s Domain Animation • Use a marker to trace a particles motion as the wave travels through the medium. • How does the particle move with respect to the direction of the wave?

  9. Transverse wave (sometimes called a sine curve or wave) • Waves that move the medium at right angles to the direction in which the waves are traveling is called a transverse wave 3:15min. • Transverse means across. The highest parts are called crests the lowest parts are called troughs.

  10. Draw & Label a Transverse Wave

  11. Compressional or Longitudinal Wave • Matter vibrates in the same direction as the wave travels. • Longitudinal discussion 3:36 min

  12. Compressional or Longitudinal wave • The parts, where the coils are close together are called compressions, the parts where the coils are spread out are called rarefactions. • Teacher’s Domain animation

  13. Draw & Label a Compressional/Longitudinal Wave

  14. Longitudinal & Transverse Wave Animation • Longitudinal & Transverse Wave Animation #2

  15. Combinations of waves • Surface waves are a combination of transverse and longitudinal waves. The waves occur at the surface between water and air. • Surface Wave Animation • Summary of Waves

  16. Summary of Waves - NASA Launch Pad Video Clip

  17. Review, Review, Review… • What does a wave carry? • How can waves be generated? • Compare and contrast a longitudinal and transverse wave.

  18. Properties of Waves

  19. Basic Properties of Waves • Amplitude • Wavelength • Frequency • Speed

  20. Amplitude • Amplitude is the maximum (displacement) distance the particles of the medium carrying the wave move away from their rest positions. • The farther the medium moves as it vibrates the larger the amplitude of the resulting waves. The greater the amplitude the greater the amount of energy.

  21. Amplitude of transverse waves • The amplitude of a transverse wave is the maximum distance the medium moves up or down from its rest position. • You can find the amplitude of a transverse wave by measuring the distance from rest to crest or rest to trough.

  22. Amplitude of a longitudinal wave. • The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes.

  23. Same frequencies, same wavelengths, different amplitudes, different energy

  24. Wavelength • A wave travels a certain distance before it starts to repeat. The distance between two corresponding parts of a wave is its wavelength. • Transverse measure from crest to crest or trough to trough. • Longitudinal measure from one compression to the next.

  25. Frequency • The number of complete waves that pass a given point in a certain amount of time. • AKA number of vibrations per second. • Frequency measured in hertz (Hz) named after Heinrich Hertz who discovered radio waves in 1886. • Frequency Animation

  26. Period • The period of a wave is the time for a particle to make one complete cycle.

  27. Pair Share 1. Is there a relationship between wavelength and frequency? What is it? 2. Is there a relationship between frequency and period? What is it? 3. Is there a relationship between amplitude and frequency? What is it?

  28. Yes. A decrease in the wavelength increases the frequency and vice versa. • Yes. An increase in the frequency will increase the period and vice versa. • NO! Putting a lot of energy into a wave will not affect the wavelength, the frequency or the speed of the wave. The energy imparted to a wave will only affect the amplitude of that wave.

  29. Speed • The speed, wavelength, and frequency of a wave are related to each other by a mathematical formula. • Speed = wavelength x frequency • Frequency = speed/wavelength • Wavelength = speed/frequency

  30. Speed • What can effect the speed of a wave? • Wave speed depends upon the medium through which the wave is moving. Only an alteration in the properties of the medium will cause a change in the speed.

  31. Speed • Waves in different mediums travel at different speeds. However, in a given medium and under the same conditions the speed of the wave is constant.

  32. 1. A teacher attaches a slinky to the wall and begins introducing pulses with different amplitudes. Which of the two pulses (A or B) below will travel from the hand to the wall in the least amount of time? Justify your answer.

  33. They reach the wall at the same time. Don't be fooled! The amplitude of a wave does not affect the speed at which the wave travels. Both Wave A and Wave B travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels.

  34. 2. The teacher then begins introducing pulses with a different wavelength. Which of the two pulses (C or D) will travel from the hand to the wall in the least amount of time ? Justify your answer.

  35. They reach the wall at the same time. Don't be fooled! The wavelength of a wave does not affect the speed at which the wave travels. Both Wave C and Wave D travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels.

  36. 3. Two waves are traveling through the same container of nitrogen gas. Wave A has a wavelength of 1.5 m. Wave B has a wavelength of 4.5 m. The speed of wave B must be ________ the speed of wave A. • a. one-ninth • b. one-third • c. the same as • d. three times larger than

  37. Answer: C • The medium is the same for both of these waves ("the same container of nitrogen gas"). Thus, the speed of the wave will be the same. Alterations in a property of a wave (such as wavelength) will not affect the speed of the wave. Two different waves travel with the same speed when present in the same medium.

  38. 4. TRUE or FALSE: • Doubling the frequency of a wave source doubles the speed of the waves.

  39. FALSE! • The speed of a wave is unaffected by changes in the frequency.

  40. 5. A wave is introduced into a thin wire held tight at each end. It has an amplitude of 3.8 cm, a frequency of 51.2 Hz and a distance from a crest to the neighboring trough of 12.8 cm. Determine the period of such a wave.

  41. Answer: 0.0195 sec • Here is an example of a problem with a lot of extraneous information. The period is simply the reciprocal of the frequency. In this case, the period is Period T =___1___ • 51.2 Hz • T = 0.0195 seconds.

  42. 6. Frieda the fly flaps its wings back and forth 121 times each second. The period of the wing flapping is ____ sec.

  43. Answer: 0.00826 seconds • The quantity 121 cycles/second (times/second) is the frequency • T (period)=___1__sec__ 121 T(period)= 0.00826 s

  44. 7. A tennis coach paces back and forth along the sideline 10 times in 2 minutes. The frequency of her pacing is ________ Hz. • a. 5.0 • b. 0.20 • c. 0.12 • d. 0.083

  45. Answer: D • Frequency refers to the number of occurrences of a periodic event per time and is measured in cycles/second. In this case, there are 10 cycles per 2 minutes (also known as 10 cycles per 120 seconds). So the frequency is • f =10 cycles • 120 s • f= 0.0833 cycles/s

  46. Cicadas produce a buzzing sound that has a wavelength in air of 2.69 m. If the speed of sound in air is 346 m/s, what is the frequency of the sound produced by a cicada? What is its period?

  47. One of the largest organ pipes is in the auditorium organ in the convention hall in Atlantic City, New Jersey. The pipe is 38.6 ft long and produces a sound with a wavelength of about 10.6 m. If the speed of sound in air is 346m/s, what is the frequency of this sound?

  48. A wave with a frequency of 60 Hz (cycles/second) travels through vulcanized rubber with a wavelength of .90 m. What is the speed of wave?

  49. A wave with a frequency of 60 Hz (cycles/second) travels through steel with a wavelength of 85.5 m. What is the speed of this wave?

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