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Rotating platform on top of another rotating platform

  1. Dec 3, 2015 #1
    1. The problem statement, all variables and given/known data
    Have platform A that is being spun by a centrifuge with a radius R1 and centripetal velocity of w1. On top of platform A is a Lazy Susan (Platform B) that spins about a radius R2 with a centripetal velocity of w2. There are accelerometers placed on the the purple platform (see pic). Estimate what the accelerometer readings will be.

    2. Relevant equations
    a_c = R*w^2

    3. The attempt at a solution
    I'm thinking the accelerometers readings would be the centripetal acceleration. I'm able to get the centripetal acceleration of Platform A and Platform B separately however I'm not sure whether the accelerometers would read the addition of these a_c or not. Please help!

  2. jcsd
  3. Dec 3, 2015 #2


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    Hi Don, :welcome:

    You sure this is the right picture? Where is A? B? Rotation axes? accelerometer postions? And which (x, y, z?) acceleration do they ,measure ?
  4. Dec 3, 2015 #3


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    The relationship between the two axes of rotation is unclear. Are they the same? Parallel? Orthogonal?
  5. Dec 3, 2015 #4
    Hi BvU,

    Here is another picture showing the rotation Axis....Platform A is the gray box and Platform B is the blue platform in the pictures. R1 is the radius of the centrifuge's arm and R2 would be approximately the length/2 of Platform B.

  6. Dec 3, 2015 #5
    Sorry please see my latest post in the thread
  7. Dec 3, 2015 #6
    Yes, sorry for that. Please see latest post on the thread
  8. Dec 3, 2015 #7


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    Ok. First you don't mean centripetal velocity. That would mean the same as radial velocity (if it means anything.). The term here is angular velocity.
    Accelerations are vectors, so can be added. Find tha acceleration of the Lazy Susan relative to the main axis, then add the acceleration of the accelerometer relative to the Lazy Susan axis. That's nontrivial since the second varies as the Lazy Susan rotates around the main axis, so you need to include variables representing the instantaneous position of the LS.
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