Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Waves

9,279 views

Published on

Published in: Technology, Education

Waves

  1. 1. Waves and Vibrations
  2. 2. Objectives <ul><li>describe the difference between a longitudinal wave and a transverse wave </li></ul><ul><li>identify the parts of a wave </li></ul><ul><li>calculate wave speed when frequency and wavelength are given </li></ul>
  3. 3. Key Terms
  4. 4. Waves are everywhere in nature <ul><ul><li>Sound waves </li></ul></ul><ul><ul><li>light waves </li></ul></ul><ul><ul><li>radio waves </li></ul></ul><ul><ul><li>microwaves </li></ul></ul><ul><ul><li>water waves </li></ul></ul><ul><ul><li>telephone cord waves </li></ul></ul><ul><ul><li>stadium waves </li></ul></ul><ul><ul><li>earthquake waves </li></ul></ul><ul><ul><li>waves on a string </li></ul></ul><ul><ul><li>slinky waves </li></ul></ul>
  5. 5. What is a wave? <ul><li>a wave is a disturbance that travels through a medium from one location to another. </li></ul><ul><li>the wave is the motion of a disturbance </li></ul>
  6. 6. Slinky Wave <ul><li>Let’s use a slinky wave as an example. </li></ul><ul><li>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 </li></ul><ul><li>To create a wave here we must first create a disturbance. </li></ul>
  7. 7. Slinky Wave <ul><li>One way to do this is to quickly push the slinky forward </li></ul><ul><li>the disturbance moves down the slinky </li></ul><ul><li>this disturbance that moves down the slinky is called a pulse . </li></ul>
  8. 8. Slinky Wave
  9. 9. Slinky Wave <ul><li>This disturbance would look something like this </li></ul><ul><li>This type of wave is called a LONGITUDINAL wave. </li></ul><ul><li>The pulse is transferred through the medium of the slinky, but the slinky itself does not actually move. </li></ul><ul><li>So what really is being transferred? </li></ul>
  10. 10. Slinky Wave <ul><li>Energy is being transferred. </li></ul><ul><li>The metal of the slinky is the MEDIUM in that transfers the energy pulse of the wave. </li></ul><ul><li>The medium ends up in the same place as it started … it just gets disturbed and then returns to it rest position. </li></ul><ul><li>The same can be seen with a stadium wave . </li></ul>
  11. 11. Longitudinal Wave <ul><li>In a longitudinal wave, the medium particles vibrate parallel to the motion of the pulse. </li></ul><ul><li>This is the type of wave that transfers sound. </li></ul>
  12. 12. Transverse waves <ul><li>A second type of wave is a transverse wave. </li></ul><ul><li>Remember, in a longitudinal wave the pulse travels in a direction parallel to the disturbance. </li></ul><ul><li>In a transverse wave the pulse travels perpendicular to the disturbance. </li></ul>
  13. 13. Transverse Waves <ul><li>The differences between the two can be seen </li></ul>
  14. 14. Transverse Waves <ul><li>Transverse waves occur when we wiggle the slinky back and forth. </li></ul>
  15. 15. Transverse v. Longitudinal
  16. 16. Anatomy of a Wave <ul><li>Now we can begin to describe the anatomy of our waves. </li></ul><ul><li>We will use a transverse wave to describe this since it is easier to see the pieces. </li></ul>
  17. 17. Anatomy of a Wave <ul><li>In our wave here the blue line is the wave and the solid grey line is the equilibrium position </li></ul><ul><li>Once the medium is disturbed, the medium moves away from equilibrium and then returns to it </li></ul>equilibrium
  18. 18. Anatomy of a Wave <ul><li>The points A and B are called the CRESTS of the wave. </li></ul><ul><li>This is the point where the wave exhibits the maximum amount of positive or upwards displacement </li></ul>A B crest
  19. 19. Anatomy of a Wave <ul><li>Point C is called the TROUGH of the wave. </li></ul><ul><li>This is the point where the wave exhibits its maximum negative or downward displacement. </li></ul>C trough
  20. 20. Anatomy of a Wave <ul><li>The height of the wave – as measured from equilibrium to crest is called the amplitude </li></ul><ul><li>This is the maximum displacement that the wave moves away from its equilibrium. </li></ul>Amplitude A crest
  21. 21. Anatomy of a Wave <ul><li>The distance between two consecutive similar points (in this case two crests) is called the wavelength . </li></ul><ul><li>Between what other points is can a wavelength be measured? </li></ul>wavelength
  22. 22. Wave frequency <ul><li>We know that frequency measures how often something happens over a certain amount of time. </li></ul><ul><li>A wave’s frequency is measured by how many complete waves pass a fixed point in a certain amount of time </li></ul>
  23. 23. Wave frequency <ul><li>Suppose I wiggle a slinky back and forth, and count that 6 waves pass a point in 2 seconds. What would the frequency be? </li></ul><ul><li>3 waves / second </li></ul><ul><li>3 Hertz </li></ul><ul><li>Hertz = Hz. </li></ul>
  24. 24. Wave frequency <ul><li>Suppose I wiggle a slinky back and forth, and count that 27 waves pass a point in 1 second. What would the frequency be? </li></ul><ul><li>27 waves / second </li></ul><ul><li>27 Hertz </li></ul>
  25. 25. Wave frequency <ul><li>Can you create a formula for frequency? </li></ul><ul><li>frequency = # of waves that pass by / time </li></ul><ul><li>Frequency is measured in Hertz (Hz) </li></ul>
  26. 26. Wave Speed <ul><li>Think back to what you know about motion: what is the formula for speed? </li></ul><ul><li>speed = distance / time </li></ul><ul><li>so to calculate speed, we need to know two things: </li></ul><ul><li>1. distance </li></ul><ul><li>2. time </li></ul>
  27. 27. Wave Speed <ul><li>Let’s apply what we know about speed to waves: </li></ul><ul><li>A set of waves passes a point 5 times in one second (5 Hz) </li></ul><ul><li>Each wave is 4 cm long </li></ul><ul><li>What is the total distance traveled? </li></ul><ul><li>How long does it take the waves to travel this distance? </li></ul>
  28. 28. Wave Speed <ul><li>5 waves that are 4 cm long each = 20 cm </li></ul><ul><li>it takes these five waves one second to pass by </li></ul><ul><li>speed = distance/time </li></ul><ul><li>what’s the wave’s speed? </li></ul><ul><li>Answer = 20 cm/s </li></ul>
  29. 29. Wave Speed <ul><li>Here’s another problem: </li></ul><ul><li>10 waves pass by in two seconds (5 Hz) </li></ul><ul><li>each wave is 3 m in length </li></ul>
  30. 30. Wave Speed <ul><li>Total distance = 30m </li></ul><ul><li>time = 2s </li></ul><ul><li>Speed? </li></ul><ul><li>Answer: 15m/s </li></ul>
  31. 31. Wave Speed <ul><li>The problems I’m giving you can be reasoned out… </li></ul><ul><li>but what if you wanted (or needed) a formula? </li></ul>
  32. 32. Wave Speed Formula <ul><li>Let’s look at another problem with easy numbers: </li></ul><ul><li>5 waves pass by in a second; each wave is 2 cm long </li></ul><ul><li>the total distance traveled by all waves is 10 cm, the time it takes them to pass by is 1 second, so the speed is 10 cm/s </li></ul>
  33. 33. Wave Speed Formula <ul><li>5 waves pass by in a second (frequency); each wave is 2 cm long (wavelength) </li></ul><ul><li>the speed is 10 cm/s </li></ul><ul><li>what is the relationship between the speed, frequency, and wavelength in the problem? </li></ul>
  34. 34. Wave Speed Formula <ul><li>If given frequency (Hz or waves/s), and wavelength, the formula for wave speed is: </li></ul><ul><li>frequency x wavelength = wave speed </li></ul>
  35. 35. Exit Slip <ul><li>Describe the differences between a longitudinal and transverse wave. </li></ul><ul><li>Draw a transverse wave and label the wavelength, amplitude, crest, and trough. </li></ul><ul><li>If the wavelength is 20 cm and frequency is 5Hz, what is the wave’s speed? SHOW YOUR WORK! </li></ul>

×