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IYPT 2015 Problem 15, screenshot from reference kit

Hi group,

I am a HS student in China preparing for a regional Young Physicist Tournament even. We are very puzzled about why would there be such movement. We would be grateful to see any inspiring replies. Thank you!

Update: As I dig through the relevant literatures (such as a royal soc. proc. A paper) on the 'Bristle-Bots'(BBots), it becomes clear why and how brushes mounted with eccentric motors attain locomotion, both qualitatively and quantitatively. HOWEVER, I am still quite puzzled by the problem to quantitatively predict the movement of an unmodified brush placed on a vibrating surface. The primary obstacles are as follows: 1. Contact force calculation (bristle and surface) 2. Internal forces within the brush system, so as to understand the deformation and change of the center of mass 3. Motion function of time derivation (The Sum Up...)

Thanks for reading the post!

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    $\begingroup$ I suspect where the bristles touch the surface not completely vertical there is a ratchet action. $\endgroup$ – Mike Dunlavey Apr 23 '15 at 13:20
  • $\begingroup$ Thanks for the reply! The ratchet effect seems interesting! When I vertically compress the free brush, its center of mass would slightly move forward. As I remove the compression, apparently, the center of mass remained in the same place, and the bristles touch the floor at a different location. Does the ratchet effect contribute to the minuscule movement initiated by pressing? Thanks for reading my long comment! $\endgroup$ – user202531 Apr 23 '15 at 16:44
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There are toys based on the same principle.

enter image description here

There is a video showing the motion, but ignore that and read the description below the video.

Note that many of the the bristles on your brush are angled and not perpendicular to the floor.

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  • $\begingroup$ Thanks for the reply. I am aware that there is a vibrating motor mounted on the brush; however, is such model equivalent to a brush placed on a vertically oscillating surface? Thanks! $\endgroup$ – user202531 Apr 23 '15 at 16:39

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