Wave Energy Transfer & Sound Wave Energy

1. Wave Energy Transfer & Sound Wave Energy

2. If a vibrational disturbance occurs, energy travels out in all directions from the vibrational source. Ripple demo

3. All points on a wave that are inphase comprise a wave front.

4. Wavefronts join points in phase.

5. Rays – a ray is an arrow sketched through the wave fronts (perpendicular) to show direction of wave propagation.

6. Rays

7. Waves transfer energy Rate of E transfer is proportional to the A . Less energy More energy

8. For light increased amplitude increases brightness.

9. For sound: increased amplitude increases volume.

10. What does wave frequency (f) determine? • Wave type for EM waves. • Color for light. • Pitch for sound

11. Hear different frequencies Sound • http://www.fearofphysics.com/Sound/sounds.html

12. Sound is a Mechanical Longitudinal/Compressional Wave

13. Sound velocity Increasing velocity solid liquid gas In gas hot faster. cold slower.

14. The Doppler Effect Stationary Source Emitting Waves all Directions. Circular wavefronts have = l & f.

15. Doppler Effect from Moving Source In front of source l is less, behind l is longer.

16. In front of source -short l higher f:hear higher pitch sound- see shorter l light (blue). behind source - longer l lower f: hear lower pitch sound see longer l light (red).

17. Doppler Effect When objects are in relative motion:a) Toward each other, f received increases.b) Away from each other, f received decreases.

18. Doppler Clip 3.1 minutes • http://www.youtube.com/watch?v=Kg9F5pN5tlI • https://www.youtube.com/watch?v=h4OnBYrbCjY

19. Resonance & Sympathetic Vibration

20. *Fact* All objects have a natural frequency of vibration. Resonance- the inducing of vibrations of a natural rate by a vibrating source having the same frequency “sympathetic vibrations”

21. Push at natural frequency, amplitude increases

22. Resonance: • An oscillatory system that is driven by a force with a f = to its natural f. • System will resonate – amplitude will increase. • The natural frequency of objects is the frequency that produces a standing wave in the object. • Can occur from reflection causing a standing wave. Amplitude is increased.

23. Sympathetic Vibration when a wave is near an object & is vibrating at the natural frequency of the object. Object vibrates sympathetically at same frequency – they resonate. Causes the amplitude to increase.

24. Break the glass 20 sec. http://www.youtube.com/watch?v=17tqXgvCN0E

25. Standing Waves on Guitar String ½ l.

26. hwk Rd Text 13 – 1 and 13-2 Wksht Review concepts sound.

27. hwk Rd 13 – 1 & pg 491 – 493 p.507 #1, 3, 6-8, 11-13, 15, 16

28. The three components of sound are: • Pitch (how high or low) • Loudness (volume) • Timbre (tone color)

29. Pitch • Vibration patterns are also called waveforms. • Each repetition of a waveform is called a cycle. • We can hear frequencies between 20 hertz to 20 kHz i.e. 20,000 Hz.

30. When the frequency of a sound doubles we say that the pitch goes up an octave. • We can hear a range of pitches of about ten octaves. • Many animals can make sounds and hear frequencies that are beyond what we can hear.

31. Loudness • To create vibration energy is used. • The greater amount of energy used the louder the sound. • The strength of the changes in air pressure made by the vibrating object determines loudness.

32. As the distance from the source increases the amount of power is spread over a greater area. • The amount of power per square meter is called the intensity of the sound.

33. Humans do not perceive sound intensity linearly. • For us to perceive a sound as twice as loud its intensity must be ten times greater. • The perceived intensity level of sound is measured in a logarithmic scale using a unit called the decibel (dB).

34. The scale begins (0 dB) on the softest sound that a person can hear. This is called the threshold of hearing. The scale ends at the volume that causes pain (120 dB) and is therefore called the threshold of pain.

35. Tacoma Narrows Bridge

36. mechanical universe resonance

37. “Timbre” (TAM-ber) or tone color is the specific property of sound that enables us to determine the difference between a piano and a harp.

38. A broad variety of tone colors exist because most sounds we perceive as pitch contain many frequencies. • The predominant pitch is called the fundamental frequency. It is the longest l that forms a standing wave.

39. Standing Wave patterns form notes.Each string or pipe vibrates with particular frequencies of standing waves.Other frequencies tend to die out.

40. Although we would perceive a string vibrating as a whole, it vibrates in a pattern that appears erratic producing many different overtone pitches. What results are particular tone colors or timbres of instruments and voices.

41. Waveform with overtones.

42. Frequencies which occur along with the primary note are called the harmonic or overtone series. When C is the fundamental the pitches below represent its first 15 overtones.

43. Harmonics There are several standing waves which can be produced by vibrations on a string, or rope. Each pattern corresponds to vibrations which occur at a particular frequency and is known as a harmonic.

44. The lowest possible frequency at which a string could vibrate to form a standing wave pattern is known as the fundamental frequency or the first harmonic.

45. 2nd Harmonic

46. Which One??

47. String Length L, l & HarmonicsStanding waves can form on a string of length L, when the l can = ½ L, or 2/2 L, or 3/2L etc.Standing waves are the overtones or harmonics.L = nln. n = 1, 2, 3, 4 harmonics. 2

48. Harmonic Frequencies Substitute v/f for l. form where ½ l can fit the string exactly. To calculate f:

49. 1st standing wave forms when l = 2L First harmonic frequency is when n = 1 as below. When n = 1 f is fundamental frequency or 1st harmonic.

50. Other standing waves with smaller wavelengths form other frequencies that ring out along with the fundamental. For second harmonic n = 2. f2 = v/L