Rotating platform on top of another rotating platform

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Homework Help Overview

The problem involves two rotating platforms: Platform A, which is driven by a centrifuge, and Platform B, a Lazy Susan that rotates on top of Platform A. The task is to estimate the readings from accelerometers placed on Platform B, considering the centripetal velocities and accelerations of both platforms.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the nature of the accelerometer readings, questioning whether the readings represent the sum of the centripetal accelerations from both platforms. There is also uncertainty regarding the relationship between the axes of rotation and the positions of the accelerometers.

Discussion Status

Participants are actively seeking clarification on the setup and relationships between the platforms. Some guidance has been offered regarding the need to consider angular velocity instead of centripetal velocity, and the complexity of adding vector accelerations has been acknowledged.

Contextual Notes

There is ambiguity regarding the orientation and relationship of the rotation axes, as well as the specific accelerometer measurements (e.g., which components of acceleration are being measured). Participants are encouraged to clarify these aspects further.

The Don
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Homework Statement


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.

Homework Equations


a_c = R*w^2

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!

upload_2015-12-3_12-27-28.png
 
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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 ?
 
The relationship between the two axes of rotation is unclear. Are they the same? Parallel? Orthogonal?
 
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.

upload_2015-12-3_13-14-58.png
 
BvU said:
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 ?
Sorry please see my latest post in the thread
 
haruspex said:
The relationship between the two axes of rotation is unclear. Are they the same? Parallel? Orthogonal?
Yes, sorry for that. Please see latest post on the thread
 
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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