Calculating Rotational Speed Change When Adding Mass to a Rotating Object"

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SUMMARY

The discussion focuses on the impact of adding a 1 lb. mass to the central axis of a rotating 40 lb. mass and how it affects the rotational speed. The change in speed is contingent upon the shapes of the masses involved, specifically their moment of inertia. The relationship between the added mass and the rotational speed change does not follow a simple inverse square law; rather, it is influenced by the distribution of mass and angular momentum. Understanding these concepts is crucial for accurately predicting the effects of mass addition on rotational dynamics.

PREREQUISITES
  • Understanding of angular momentum
  • Knowledge of moment of inertia
  • Familiarity with rotational dynamics
  • Basic principles of mass distribution
NEXT STEPS
  • Research the principles of angular momentum conservation
  • Study the calculations for moment of inertia for various shapes
  • Explore the effects of mass distribution on rotational speed
  • Investigate real-world applications of rotational dynamics in engineering
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Physics students, mechanical engineers, and anyone interested in the principles of rotational dynamics and mass effects on speed changes.

rdmachinist
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If a rotating 40 lb. mass has a non rotating 1 lb. mass instantly added to it's central axis, how much will the rotating mass slow down? Secondly, all else equal, does the rotational speed change the proportionality with which the smaller mass slows the larger (inverse square or some such law)?
 
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rdmachinist said:
If a rotating 40 lb. mass has a non rotating 1 lb. mass instantly added to it's central axis, how much will the rotating mass slow down? Secondly, all else equal, does the rotational speed change the proportionality with which the smaller mass slows the larger (inverse square or some such law)?
There's not enough information to answer the question: it depends on the shapes of the masses. Assuming a vertical axis:
  • If the large mass was tall and thin, and the small mass was short and fat, the large mass would slow down a lot.
  • If the large mass was short and fat, and the small mass was tall and thin, the large mass wouldn't slow very much.
Do you know about angular momentum? Or moment of inertia?
 
I'll look into these terms more thoroughly and repost at a later date if nessesary. Thanks for the reply.
 

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