1 / 37

Cutting the A ir

2. Cutting the A ir. Kamila Součková. Task. When a piece of thread (e.g., nylon) is whirled around with a small mass attached to its free end, a distinct noise is emitted. Study the origin of this noise and the relevant parameters . . Hypotheses for Origin of the Sound.

nedaa
Download Presentation

Cutting the A ir

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 2. Cutting the Air Kamila Součková

  2. Task When a piece of thread (e.g., nylon) is whirled around with a small mass attached to its free end, a distinct noise is emitted. Study the origin of this noise and the relevant parameters.

  3. Hypotheses for Origin of the Sound

  4. H1: String vibrations • cause of vibration: air flowing around • characteristic: multitude of resonant frequencies example: guitar string

  5. String Vibrations:Resonant frequencies • (copper wire) • : frequency of sound • : length of thread • :centripetalforce – tension • : linear density any effect will be seen inexperiment

  6. H2: Vortex shedding • turbulences of air • periodic disturbances in air flow • : frequency of sound • : Strouhal’s Number • (empirical constant) • :velocity • : diameter of thread

  7. Experiments Decide

  8. Experimental Apparatus • Rotation: by hand • Position of microphone: on the axis of rotation(preventing Doppler effect) Microphone • : frequency of rotation • : diameter of thread • : frequency of sound Thread Mass

  9. experiment #1:Length of thread

  10. Length of of thread D = 1 mm f = 4 Hz stringvibrations

  11. Frequency of sound depending on length of thread vortex shedding:

  12. Frequency of sound depending on length of thread vortex shedding:

  13. experiment #2:Velocity

  14. Frequency of sound depending on rotation frequency • Effectively the same as lengthening

  15. vortex shedding:

  16. vortex shedding:

  17. experiment #2:Wire Thickness

  18. Thicknessofthread L = 1m f = 4 Hz

  19. Frequencyofsoundvs.thickness vortex shedding:

  20. Frequencyofsoundvs.thickness vortex shedding:

  21. What Can Be Inferred? ✔ ✘ ✔

  22. Massatthe end D = 0,6 mm L = 0,4 m f = 5 Hz Nothingchanges • Stringvirations– negligible • weight (tension) isunimportant

  23. Surfaceofmass • Smallsurface (according to task) – negligibleeffect D = 0,4 mm L = 0,4 m f = 5 Hz 2 2 2 2 2

  24. Significantlylargesurfaceofmass D = 0,2 mm L = 0,3 m f = 5 Hz 2 2 2 Noticeableeffect, butoutoftask....

  25. What Can Be Inferred? ✔ ✔ ✘ ✔ ✔ ✘ ✘ ✔ “study the origin”

  26. Loudness

  27. Loudness • M. J. Lighthill, "On Sound Generated Aerodynamically. I. General Theory," Proc. R. Soc. Lond. A 211 (1952) pp. 564-587: intensity

  28. Loudness vs frequency of rotation

  29. Loudness vs frequency of rotation

  30. Conclusion • changing mass  no influence • great correlation with experiments ✔ ✔ ✘ ✘ 31

  31. Conclusion ✔ ✔ spectra: ✘ ✘ 32

  32. Conclusion ✔ ✔ dependency on relevant parameters: ✘ • : peak frequency • : frequency of rotation • : diameter of thread • : frequency of sound • : Strouhal’s Number • loudness ✘ 33

  33. Thank you for your attention! ✔ ✔ dependency on relevant parameters: ✘ • : peak frequency • : frequency of rotation • : diameter of thread • : frequency of sound • : Strouhal’s Number • loudness ✘ 34

  34. Thank you for your attention Marco Bodnár

  35. Appendices

  36. Loudness - frequencyofrotation Loudness log(velocity)

More Related