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Direction of percieved gravity - MIT lecture

  1. Jun 4, 2012 #1

    starting at about 24 min in this video, Prof. Lewin starts talking about whirling an object around in a circle...now he then says that the direction of percieved gravity in is in the OPPOSITE direction to the centripetal acceleration..
    would I be correct in assuming, however, that on a free body diagram, gravity will still be drawn vertically downward?? if not, why?
  2. jcsd
  3. Jun 4, 2012 #2


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    I watched all of Professor Lewin's lecture series on classical mechanics as preparation of 1st year university. I think the perceived gravity upwards is a result of the (fictitious)centrifugal force. From the perspective of the water, it is not moving in the bucket as it swirled around and so it 'invents' a centrifugal force (reminiscent of one not accelerating in a bus from one's own position) to counteract the centripetal force. Since this force is fictitious, on a free body diagram gravity would still be acting downwards.
  4. Jun 4, 2012 #3


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    earths gravity, yes. by "percieved gravity" he probably means the vector sum of earths gravity + centrifugal force in the rotating frame
  5. Jun 4, 2012 #4
    ok thanks
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