1. Waves 2 ways to transfer energy in nature: 1) Collisions Involves a transfer of matter from one place to another 2) Waves A transfer of energy without a transfer of matter ex.: bowling

2. Wave Vocabulary 2 basic types of waves: -Transverse: a wave in which the particles of the medium vibrate perpendicular to the direction of wave travel -Longitudinal: a wave in which the particles of the medium vibrate parallel to the direction of wave travel example: water waves example: waves in a Slinky

3. crest trough wavelength, λ amplitude, A Aequilibrium position Wave terms (using a transverse wave as an example): wavelength: the distance of one complete wave vibration; crest-to-crest distance (or trough-to-trough); represented by the Greek letter λ (“lambda”) amplitude: the distance from the equilibrium position to the crest of the wave; the maximum displacement of the particles

4. frequency: the number of waves that pass a certain point in one second; denoted by f ex. 20 waves pass a certain point in 10 seconds The number of waves per second = 20 waves 10 sec f = 2 waves sec = 2 hertz= 2 Hz

5. If the frequency is 2 waves per second, how long does it take one wave to pass the point? 0.5 s Period: the time it takes for one wave to pass; represented by T ex. If the frequency is 10 Hz, what is the period?T = 0.10 s T = 1 f and T 1 f =

6. Phase: a comparative description between two points on a wavefront A

7. AB Consider two locations on a wavefront, A and B Pts. A and B on the wavefront are “in phase” ; notice they are exactly one wavelength apart ; think of A and B as fishing bobbers that are bobbing up and down as a water wave passes their location C ; Pt. C is also in phase with A and B Two points on a wavefront are “in phase” when they differ by 1λ, 2λ, … nλ, where n = integer ; A and B reach a crest and the same time, and go down and reach a trough at the same time ; A and B move completely together

8. Phase: a comparative description between two points on a wavefront AB As bobber A goes up, bobber D goes down Not only are they not in phase, A and D are completely out of phase ; notice they are exactly one-half wavelength apart ; as A reaches a crest, D reaches a trough C ; they are “180 o out of phase Two points on a wavefront are “180 o out of phase” when they differ by ½ λ, 3 / 2 λ, … n / 2 λ, where n = odd integer D ; they move completely opposite to one another C and D are also 180 o out of phase, and differ by 3 / 2 wavelength

9. Depends on the material wave is passing through, the medium of travel ex. speed in deep water is different than in shallow water; Is a constant for a given medium ex. large amplitude waves travel at the same speed as small amplitude waves faster; as waves approach shore, they slow down and “break” Speed of a Wave

10. Speed can be found from: v = f λ v = speed f = frequency λ = wavelength ex. If a wave of frequency 2.0 Hz is traveling in water and has a wavelength of 0.75 m, with what speed is the wave moving? v = f λ = ( 2.0 Hz )( 0.75 m ) = 1.5 m/s

11. What is the wavelength of this wave? 1.0.5 m 2.1.2 m 3.1.5 m 4.2.4 m 2.4 m 0.50 m Quick quiz: Given the following: Dave counts 15 waves passing his location in 10 seconds

12. 1.0.5 m 2.1.2 m 3.1.5 m 4.2.4 m 2.4 m 0.50 m Dave counts 15 waves passing his location in 10 seconds λ = crest-to-crest distance

13. What is the frequency of this wave? 2.4 m 0.50 m Dave counts 15 waves passing his location in 10 seconds 1. 1.5 Hz 2. 2.4 Hz 3. 10 Hz 4. 15 Hz

14. 2.4 m 0.50 m Dave counts 15 waves passing his location in 10 seconds f = 15 waves 10 s =1.5 waves/sec 1. 1.5 Hz 2. 2.4 Hz 3. 10 Hz 4. 15 Hz

15. What is the period of this wave? 1.1.5 s 2.1.0 s 3.0.67 s 4.0.5 s 2.4 m 0.50 m Dave counts 15 waves passing his location in 10 seconds

16. 2.4 m 0.50 m Dave counts 15 waves passing his location in 10 seconds T = 1 f = = 0.67 s 1 1.5 Hz 1.1.5 s 2.1.0 s 3.0.67 s 4.0.5 s

17. What is the amplitude of this wave? 1.2.4 m 2.1.2 m 3.1.0 m 4.0.50 m 2.4 m 0.50 m Dave counts 15 waves passing his location in 10 seconds

18. 1.2.4 m 2.1.2 m 3.1.0 m 4.0.50 m 2.4 m 0.50 m Dave counts 15 waves passing his location in 10 seconds A A Amplitude = distance from eq. position to crest

19. What is the speed of this wave? 1.0.75 m/s 2.3.6 m/s 3.1.6 m/s 4.1.8 m/s 2.4 m 0.50 m Dave counts 15 waves passing his location in 10 seconds

20. 1.0.75 m/s 2.3.6 m/s 3.1.6 m/s 4.1.8 m/s 2.4 m 0.50 m f = 1.5 Hz λ = 2.4 m v = f λ = ( 1.5 Hz )( 2.4 m ) = 3.6 m/s

21. The energy of a wave depends on its amplitude. 1.True 2.False

22. Energy of a Wave The energy of a wave depends on its amplitude Low amplitude, low energy ex. No-wake zones prevent shore erosion

23. High amplitude, high energy Can you find the surfer?

24. ex.: tsunami

25. This is a picture of the tsunami of December 26, 2004, which washed ashore on the Thai island of Phuket (Indonesia)

26. “Hey, let’s go watch the tsunami come in.”

27. Before After Before After