A flip of the Earth on its axis

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SUMMARY

The Earth does not flip on its axis; rather, its rotational axis is stable due to the equatorial bulge and conservation of angular momentum. The discussion highlights a model using a pool cue ball filled with lead to demonstrate flipping behavior, which is not representative of Earth's dynamics. The model's instability arises from the moments of inertia, and the Earth maintains its most stable axis of rotation. Videos referenced in the discussion illustrate these principles, emphasizing the differences between rigid body models and the actual behavior of celestial bodies.

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  • Understanding of angular momentum conservation
  • Familiarity with moments of inertia
  • Knowledge of precession in rotating bodies
  • Basic principles of fluid dynamics affecting spinning objects
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  • #31
Thanks for the info!
 
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  • #32
arydberg said:
Also on the subject of table tennis balls if you weight one half of the ball. by spliting it in two, filling one half with epoxy and glueing it back together and color the weighted half it sits with the weighted half down but when spun it will flip. It is stable when spinning only with the weighted half on top. You can also drill a hole in the ball, half fill it with water. and freeze it and color the weighted half. It workes fine for a short time till the water melts.
What is the spin axis with respect to the halves?

The half filled balls give you no clear intermediate axis. And your center of mass is not the ball center, so you have substantial external torques around the CoM from the air cushion support. This is likely quite different from the typical intermediate axis flipping.
 
  • #33
In order to get the most intriguing demo, is it better to have the three principal MoIs fairly close to each other, or is it better if they are as different as possible?
 

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