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A phenomena i cant fully understnad

  1. Mar 31, 2013 #1
    when i rotate a screw at low speed he stop after sec.
    but when giving him high initial speed he rotate,stop,and rotate backwards and stop again.
    i think its because the drag force which got 2 components,1 take care of low speed velocities and the other high speed.
    i'm not fully understand that,and i hope someone can answer me.

    *sry for my bad english,lol
  2. jcsd
  3. Mar 31, 2013 #2


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    Staff: Mentor

    Where do you rotate the screw?
    The fast rotation might lead to something like a compressed (or extended) spring, which reverses the direction to extend (or compress) again afterwards.
  4. Mar 31, 2013 #3
  5. Mar 31, 2013 #4


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    Is it a very long screw? Then driving long screws into hardwood I've seen the screw twist due to the high torque. Then when you stop the twist unwinds. It is most noticible on long screws that only have a thread at the pointed end like these...

    http://www.screwfix.com/p/timberfix-plus-exterior-timber-screws-6-3-x-200mm-pk50/36687 [Broken]

    Could also be a strobe lighting effect?
    Last edited by a moderator: May 6, 2017
  6. Mar 31, 2013 #5
  7. Apr 1, 2013 #6
    If it is really just a screw I don't think the rattleback explanation works. What is probably happening, is that the screw can roll up on its thread at the tip a bit, when it is spun fast enough. When it comes to a rest it rolls back so the thread at the tip points up again. But if you don't think that is the reason, maybe you should make a video.
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