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# Introduction to Waves

Introduction to Waves. How do you describe the motion of a pulse traveling through the slinky?. Watch the video clip: Making_Pulses Sketch what you observe. Draw a picture of a pulse and label the parts including: amplitude and equilibrium (rest position).

## Introduction to Waves

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### Presentation Transcript

1. Introduction to Waves

2. How do you describe the motion of a pulse traveling through the slinky? Watch the video clip: Making_Pulses • Sketch what you observe. Draw a picture of a pulse and label the parts including: amplitude and equilibrium (rest position).

3. How do you describe the motion of a pulse traveling through the slinky? Watch the video clip: Making_Pulses • Sketch what you observe. Draw a picture of a pulse and label the parts including: amplitude and equilibrium (rest position). Amplitude Equilibrium position Pulse Length

4. Is the speed of a pulse constant? • Propagating_Pulses.mov Create a position vs. time graph. Use the meterstick in the background for a distance scale. The video frame rate is 30 frames per second, so the time elapsed between frames is 1/30 s.

5. Pulse Speed The graph should be linear… so the speed is constant!

6. How do you describe the motion of a particle in the spring as a pulse passes through? Tie a string to the midpoint of a slinky. Send a pulse through the slinky and describe the movement of the string.

7. How do you describe the motion of a particle in the spring as a pulse passes through? Motion of particle in spring/slinky is perpendicular to the motion of the pulse! We call this a TRANSVERSE pulse.

8. What is the difference between a pulse and a wave? Pulse = Single event Wave = Multiple pulses sent continuously Amplitude Amplitude Wave length =  Pulse length Wave Pulse

9. How do you calculate the speed of a pulse/wave? 1. Speed = distance / time  2. Speed = wavelength * frequency =  f 3. Speed = T= tension of string/slinky = linear mass density or mass/length

10. Fixed and Free End (Assuming no Friction) • What happens to the amplitude of a pulse as it travels down the slinky and back? • What happens to the speed of a pulse as it travels down the slinky and back?

11. Fixed and Free End (Assuming no Friction) • What happens to the amplitude of a pulse as it travels down the slinky and back? Stays the same • What happens to the speed of a pulse as it travels down the slinky and back?

12. Fixed and Free End (Assuming no Friction) • What happens to the amplitude of a pulse as it travels down the slinky and back? Stays the same • What happens to the speed of a pulse as it travels down the slinky and back? Stays the same

13. Fixed vs. Free End What is the shape of the pulse after it comes back down the slinky after hitting the fixed end? Fixed End What is the shape of the pulse after it comes back down the slinky after hitting the free end? Free End

14. Fixed vs. Free End What is the shape of the pulse after it comes back down the slinky after hitting the fixed end? Inverted What is the shape of the pulse after it comes back down the slinky after hitting the free end? Upright

15. Interacting at a Boundary–Reflection and Transmission Involving Two Media Condition Reflection (I or U) Transmission (I, U or N) Slinky  Fixed End Slinky  Snaky Snakey  Slinky Snakey  Free End

16. Interacting at a Boundary–Reflection and Transmission Involving Two Media Condition Reflection Transmission Slinky  Fixed End Inverted None Slinky  Snaky Snakey  Slinky Snakey  Free End

17. Interacting at a Boundary–Reflection and Transmission Involving Two Media Condition Reflection Transmission Slinky  Fixed End Inverted None Slinky  Snaky Inverted Upright Snakey  Slinky Snakey  Free End

18. Interacting at a Boundary–Reflection and Transmission Involving Two Media Condition Reflection Transmission Slinky  Fixed End Inverted None Slinky  Snaky Inverted Upright Snakey  Slinky Upright Upright Snakey  Free End

19. Interacting at a Boundary–Reflection and Transmission Involving Two Media Condition Reflection Transmission Slinky  Fixed End Inverted None Slinky  Snaky Inverted Upright Snakey  Slinky Upright Upright Snakey  Free End Upright None

20. Superposition- What happens when waves or pulses interact? 1. Two pulses from opposite sides: opposite superposition 2. Two pulses from same side: same superposition

21. Superposition- What happens when waves or pulses interact? • Two pulses from opposite sides: 2. Two pulses from same side: same superposition

22. Superposition- What happens when waves or pulses interact? • Two pulses from opposite sides: 2. Two pulses from same side:

23. Standing Waves When we send pulses down string or slinky at certain frequencies we produce standing waves… let’s see an example. Standing Wave Movie

24. Do you see a pattern for calculating frequency for each standing wave?

25. Two Fixed End Standing Waves Frequency for a standing wave produced with two fixed ends with n antinodes. n = 1, 2, 3… Antinode Node

26. What if only one end was fixed…

27. Do you see a pattern for calculating frequency for each standing wave?

28. One Fixed End Standing Waves Frequency for a standing wave produced with one fixed end n = 1, 3, 5…

29. Sound! Two major differences Longitudinal Wave Speed

30. Speed of Sound Speed = B = bulk modulus is the mathematical description of an object or substance's tendency to be deformed elastically  = density Sound is faster in a more elastic and less dense medium.

31. Sound is a Longitudinal Wave Particle motion is parallel to motion of wave or pulse.

32. Superposition Amplitude = Loudness… Constructive Interference = LOUD Destructive Interference= no sound

33. Interference of Sound Waves Constructive Interference: Path Difference is zero or some integer multiple of wavelengths d = 0, 1, 2, 3,…. Destructive Interference: Path Difference is ½ , 1 ½ , 2 ½ , etc wavelengths d = ½ , 3/2 , 5/2 ,….

34. Path length difference is 0. Two wave crests will meet creating constructive . LOUD 2  2  Path length difference is 1/2 . Wave crest and trough will meet creating destructive interference…. No sound. 2  3/2 

35. Interference Example Two speakers placed 3.00 m apart are driven by the same oscillator. A listener is originally at point O, which is located 8.00 m from the center of the line connecting the two speaker. The listener then walks to point P, which is perpendicular to the distance 0.350 m from O, before reaching the first minimum in sound intensity. What is the frequency of the oscillator? Take the speed of sound in air to be 343 m/s. (Minimum = no sound) 8.0 m O 3.0 m 0.350 m P

36. Interference Example Path length for speaker 1 =8.211 O 3.0 m 8.0 m 0.350 m P Path length for speaker 2 = 8.08 m Two speakers placed 3.00 m apart are driven by the same oscillator. A listener is originally at point O, which is located 8.00 m from the center of the line connecting the two speaker. The listener then walks to point P, which is perpendicular to the distance 0.350 m from O, before reaching the first minimum in sound intensity. What is the frequency of the oscillator? Take the speed of sound in air to be 343 m/s. (Minimum = no sound)

37. Interference Example Path length for speaker 1 =8.21 Path length difference = 0.13 m O 3.0 m 8.0 m 0.350 m P Path length for speaker 2 = 8.08 m Two speakers placed 3.00 m apart are driven by the same oscillator. A listener is originally at point O, which is located 8.00 m from the center of the line connecting the two speaker. The listener then walks to point P, which is perpendicular to the distance 0.350 m from O, before reaching the first minimum in sound intensity. What is the frequency of the oscillator? Take the speed of sound in air to be 343 m/s. (Minimum = no sound)

38. Interference Example Path length difference = 0.13 m First minimum occurs when the difference is /2 so…. 0.13 m = /2   = 0.26 m • = 0.26 m • V = 343 m/s • So f = 1.3 kHz Two speakers placed 3.00 m apart are driven by the same oscillator. A listener is originally at point O, which is located 8.00 m from the center of the line connecting the two speaker. The listener then walks to point P, which is perpendicular to the distance 0.350 m from O, before reaching the first minimum in sound intensity. What is the frequency of the oscillator? Take the speed of sound in air to be 343 m/s. (Minimum = no sound)

39. Two identical loudspeakers face each other at a distance of 180 cm and are driven by a common audio oscillator at 680 Hz. Locate the points between the speakers along a line joining them for which the sound intensity is (a) maximum (b) minimum. Assume the speed of sound is 340 m/s.

40. Beats

41. Doppler Effect

42. Doppler Effect

43. Shock Waves

44. Standing Waves for Sound Sometimes called fundamental frequency. Can you find the pattern for the harmonic frequencies? Sometimes called first overtone. Sometimes called second overtone.

45. Standing Waves for Sound Sometimes called fundamental frequency. Can you find the pattern for the harmonic frequencies? n= 1, 2, 3… Sometimes called first overtone. Sometimes called second overtone.

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