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Waves and Vibrations

Waves and Vibrations

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Waves and Vibrations

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  1. Waves and Vibrations Let Us Entertain You!

  2. What do you know about waves? p81 • Write down 5 things that you know about waves in your notebook. Be specific and write complete sentences! • Now write 3 questions that you have about waves • Share out

  3. Sound waves, visible light waves, radio waves, microwaves, water waves, sine waves, telephone chord waves, stadium waves, earthquake waves, waves on a string, slinky waves Waves are everywhere in nature

  4. See Sounds p82 • Make some noise! • Record what you notice about the wave forms • The up/down direction is Amplitude. Describe when the amplitude gets bigger or smaller. • The left/right direction is wave length. Describe how to make the wavelength change.

  5. Rank the soundsfrom highest frequency to lowest…from loudest to quietest… p93

  6. p82 Bell JarIn Space No One Can Hear You Scream… • Describe the apparatus • Describe what happens to the noise when the vacuum pump is turned on. • Describe what happens as air reenters the bell jar. • What conclusion can be drawn about the slogan for Alien based on what we observed here?

  7. Big idea – a method of communication is a means by which information or ideas can be transferred from your mind to someone else’s (information like how to build a doghouse) p83 • Fill in the chart with the following methods of communication and give evidence for your placement: speaking/listening, writing/reading, television, morse code, braille, texting, email • How are each of the 5 senses activated by wave stimuli?

  8. Investigation #1 (p484-486)What is the effect of string length and tension on pitch? P86 • Record your observations and answer lab questions in your notebook • Get a stamp when you are done • READ p486-487 and answer CU (p487) 1-3 • Answer PtoGo (p490) 1-7 • Get another stamp

  9. Wave model physics p87 1.) The pitch of a sound corresponds to the frequency of vibration of the object producing the sound. The higher the pitch, the higher the frequency. 2.) Decreasing the length of a vibrating string increases the pitch (frequency). 3.) Increasing the tension on the string also increases the pitch (frequency) • Build your own instrument

  10. Amplitude and Wavelength • How does the sound change when the amplitude is changed? • How does the sound change when the wavelength is changed? p92

  11. What is a wave? p85 • a wave is a oscillation that travels through a medium from one location to another. There are no sound waves that can travel through space. • a wave is the motion of a disturbance • Transfer of energy (not matter) • Waves have amplitude, wavelength, crests and troughs

  12. Wave Basics p85

  13. Wave Period is the time it takes 1 wavelength to pass • Wave frequency is how many waves pass in one time period p85

  14. Investigation #2 p492-498Distinguish between longitudinal and transverse waves p88 • Part A: Stadium wave • Make a stadium wave with your class • A1. Which direction did the wave move? • A2. Which way did you move? • A3. How did the wave move without you moving in that direction? • A4. What variables can you change in your class wave (describe at least 3)?

  15. How many waves? p88 • Use a slinky to makes waves. How many different kinds of waves can you make with a slinky? Draw each kind in your notebook… • You have only 10 minutes…

  16. Part B: Transverse waves and standing waves p88 • B1. Which direction did the wave move? • B2. Which way did the tape in the middle of the slinky move? • B3. Describe a transverse wave. • B4. What word best describes a transverse wave?

  17. p89 Part C: Longitudinal waves • C1. Which direction did the wave move? • C2. Which way did the tape in the middle of the slinky move? • C3. Describe a longitudinal wave. • C4. What word best describes a longitudinal wave? • C5. What kind of wave is a stadium wave? Use slinky evidence to support your answer.

  18. p89 • Part D: Wave Interference ( waveysim worksheet…use phet wave interference sim) • Get a stamp when you finish Part D • Read p498-502. Answer Cu (p502) 1-3 • Finish intro to waves wkst (p84) • Vocab Active Physics p498-501. Define in your own words and draw a picture

  19. Wave vocab p91 • Define each vocabulary word using your own words (do not copy the book definition) and draw a picture to show the meaning of the word

  20. Exit p87 • Write down 5 things that you learned Use a physics vocabulary word in each one!)

  21. Directions: ppt slides 22-45highlight or circle gold words on pptwatch all animationsclick/watch all underlined linksanswer any questionsget each page stamped when finished P90-91 • Your wave model (what do you know about waves…list at least 5) Get stamps when finished and finish vocab

  22. Slinky Wave • Let’s use a slinky wave as an example. • When the slinky is stretched from end to end and is held at rest, it assumes a natural position known as the equilibrium or rest position. • To introduce a wave here we must first create a disturbance. • We must move a particle away from its rest position.

  23. Slinky Wave • One way to do this is to push the slinky forward • the beginning of the slinky moves away from its equilibrium position and then back. • the disturbance continues down the slinky. • this disturbance that moves down the slinky is called a pulse. • if we keep “pulsing” the slinky back and forth, we could get a repeating disturbance.

  24. Slinky Wave • This disturbance would look something like this • This type of wave is called a LONGITUDINAL wave. • The pulse is transferred through the medium of the slinky, but the slinky itself does not actually move. • It just displaces from its rest position and then returns to it. • So what really is being transferred?

  25. Slinky Wave • Energyis being transferred. • The metal of the slinky is the MEDIUM in that transfers the energy pulse of the wave. • The medium ends up in the same place as it started … it just gets disturbed and then returns to it rest position. • The same thing can be seen with a stadium wave (think back to the stadium wave we made in class).

  26. Longitudinal Wave • The wave we see here is a longitudinal wave. • The medium particles vibrate parallel to the motion of the pulse. • This is the same type of wave that we use to transfer sound. • How is sound made in your vocal cords and how does it gets to your ears? • show tuning fork demo

  27. Transverse waves • A second type of wave is a transverse wave. • We said in a longitudinal wave the pulse travels in a direction parallel to the disturbance. • In a transverse wave the pulse travels perpendicular to the disturbance.

  28. Transverse Waves • The differences between the two can be seen. List 2 differences…

  29. Transverse Waves • Transverse waves occur when we wiggle the slinky back and forth. • They also occur when the source disturbance follows a periodic motion. • A spring or a pendulum can accomplish this. • The wave formed here is a SINE wave. •

  30. Swings and Springs • Describe 1 cycle of a pendulum swing • Describe 1 cycle of a spring “bounce”

  31. Anatomy of a Wave • Now we can begin to describe the anatomy of our waves. • We will use a transverse wave to describe this since it is easier to see the pieces.

  32. In our wave here the dashed line represents the equilibrium position. Once the medium is disturbed, it moves away from this position and then returns to it Anatomy of a Wave

  33. Anatomy of a Wave crest • The points A and F are called the CRESTS of the wave. • This is the point where the wave exhibits the maximum amount of positive or upwards displacement

  34. Anatomy of a Wave • The points D and I are called the TROUGHS of the wave. • These are the points where the wave exhibits its maximum negative or downward displacement. trough

  35. Anatomy of a Wave • The distance between the dashed line and point A is called the Amplitude of the wave.\ • This is the maximum displacement that the wave moves away from its equilibrium. Amplitude

  36. Anatomy of a Wave wavelength • The distance between two consecutive similar points (in this case two crests) is called the wavelength. • This is the length of the wave pulse. • Between what other points is can a wavelength be measured?

  37. Anatomy of a Wave • What else can we determine? • We know that things that repeat have a frequency and a period. How could we find a frequency and a period of a wave? What needs to be measured?

  38. Wave frequency • We know that frequency measure how often something happens over a certain amount of time. • We can measure how many times a pulse passes a fixed point over a given amount of time, and this will give us the frequency.

  39. Wave frequencyfrequency measure how often something happens over a certain amount of time • Suppose I wiggle a slinky back and forth, and count that 6 waves pass a point in 2 seconds. What would the frequency be? • 6 waves/2 seconds = 3 cycles / second • 3 Hz • we use the term Hertz (Hz) to stand for cycles per second.

  40. Wave Period • The period describes the same thing as it did with a pendulum. • It is the time it takes for one cycle to complete. • It also is the reciprocal of the frequency. • T = 1 / f • f = 1 / T • let’s see if you get it.

  41. Wave Speed • We can use what we know to determine how fast a wave is moving. • What is the formula for velocity? • velocity = distance / time • What distance do we know about a wave • wavelength • and what time do we know • period

  42. Wave Speed • so if we plug these in we get • velocity = length of pulse / time for pulse to move pass a fixed point • v =  / T • we will use the symbol  (greek letter lambda) to represent wavelength

  43. Wave Speed • v =  / T • but what does T equal • T = 1 / f • so we can also write • v = f  • velocity = frequency * wavelength • This is known as the wave equation. • examples

  44. Wave Equation v=λf 1.) Ocean waves 12 m in length strike a seawall with a frequency of 0.5 Hz. How fast do these waves move? v=λf 2.) sound waves traveling at 350 m/s are made by a tuning fork that vibrates 384 times each second. What is the wavelength of the sound waves produced? λ=v/f 3.) The light rays from a laser pointer have a wavelength of 670nm and travel at 300Mm/s. What is the frequency of the source of these waves? f=v/λ

  45. Wave Equation v=λ/T 4.) A nurse counts 76 heartbeats in one minute. What are the period and frequency of the hearts’ oscillations? f=vibrations/time period=1/f 5.) New York’s 300m tall Citicorp Tower oscillates in the wind with a period of 6.80 s. Calculate its velocity of vibration. v=λ/T What is the frequency of the wave? f=v/λ

  46. Introduction to waves (notes) • To understand the most important thing a wave does, consider a cork floating in the still water of a pool…this is similar to a stadium wave and demonstrates that waves transfer energy without transferring matter • Finish the worksheet… p84

  47. Wave model p87 4.) Waves are disturbances that travel through a medium 5.) Only ElectroMagnetic (EM) waves can travel through a vacuum (empty space) 6.) Period = the time required for 1 cycle 7.) Frequency = cycles/time =1/period f=1/T 8.) Wave equation: wavelength λ=v/f or v =f λ 9.) Waves transfer energy from one place to another. Large amplitude=large energy

  48. p87 More Wave model physics 10.) Transverse waves have disturbances perpendicular to the wave direction. Light (and all other EM waves) are transverse. 11.) Longitudinal waves have the disturbance in the same direction as the wave. All sounds are longitudinal (which is why you lose your hearing from loud sounds) 12.) standing waves do not move. They are made of nodes and antinodes.

  49. Finding wave properties P92-93 • Phet: wave on a string simulation • Get a stamp when you finish • Wave basics wkst • Get a stamp when you finish Quiz tomorrow!

  50. Wave Behavior • Now we know all about waves: • How to describe them, measure them and analyze them.