1. Kamila Součková Cutting the Air 2.

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. 2

3. 3

4. Hypotheses for Origin of the Sound mechanism string vibrations vortex shedding (airflow) source only thread both mass and thread 4

5. H1: String vibrations cause of vibration: air flowing around characteristic: multitude of resonant frequencies example: guitar string 5

6. String Vibrations: Resonant frequencies any effect will be seen in experiment 6

7. turbulences of air –periodic disturbances in air flow H2: Vortex shedding 7

8. Experiments Decide 8

9. Experimental Apparatus Rotation: by hand Position of microphone: on the axis of rotation (preventing Doppler effect) Microphone Mass Thread 9

10. experiment #1: LENGTH OF THREAD

11. Length of of thread D = 1 mm f = 4 Hz string vibrations 11

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

13. Frequency of sound depending on length of thread vortex shedding: 13

14. experiment #2: VELOCITY

15. Effectively the same as lengthening Frequency of sound depending on rotation frequency 15

16. 16 vortex shedding:

17. 17 vortex shedding:

18. experiment #2: WIRE THICKNESS

19. Thickness of thread L = 1m f = 4 Hz 19

20. Frequency of sound vs. thickness 20 vortex shedding:

21. Frequency of sound vs. thickness 21 vortex shedding:

22. What Can Be Inferred? mechanism string vibrations vortex shedding (airflow) source thread only both mass and thread 22 ✔ ✘ ✔

23. Mass at the end String virations – negligible – weight (tension) is unimportant D = 0,6 mm L = 0,4 m f = 5 Hz Nothing changes 23

24. Surface of mass Small surface (according to task) – negligible effect D = 0,4 mm L = 0,4 m f = 5 Hz 2 2 2 2 2 24

25. Significantly large surface of mass D = 0,2 mm L = 0,3 m f = 5 Hz Noticeable effect, but out of task.... 2 2 2 25

26. What Can Be Inferred? mechanism string vibrations vortex shedding (airflow) source thread mass both 26 ✔ ✘ ✔ ✘ ✘ ✔ ✔ “study the origin” ✔

27. LOUDNESS

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

29. Loudness vs frequency of rotation

31. Conclusion 31 mechanism vortex shedding (airflow) source thread 31 ✘ ✘ ✔ great correlation with experiments changing mass  no influence ✔

32. Conclusion 32 mechanism vortex shedding (airflow) source thread 32 ✘ ✘ ✔ ✔ spectra:

33. Conclusion 33 mechanism vortex shedding (airflow) source thread 33 ✘ ✘ ✔ ✔ dependency on relevant parameters:

34. Thank you for your attention! 34 mechanism vortex shedding (airflow) source thread 34 ✘ ✘ ✔ ✔ dependency on relevant parameters:

35. THANK YOU FOR YOUR ATTENTION Marco Bodnár

36. APPENDICES

37. Loudness - frequency of rotation Loudness log(velocity) 37