Where Does the Momentum of a Rolling Ball Go?

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Discussion Overview

The discussion revolves around the fate of momentum when a heavy ball rolls to a stop due to friction. Participants explore whether momentum is lost to heat, transferred to the Earth, or conserved in some manner, touching on concepts of friction, Newton's laws, and the nature of momentum in collisions.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions where the momentum of a rolling ball goes when it stops, suggesting it may be lost to heat or cause a minuscule movement of the Earth.
  • Another participant asserts that the momentum does indeed cause the Earth to move slightly, proposing that this movement cancels out the initial shift in the center of mass when the ball was set in motion.
  • A participant seeks clarification on whether momentum is lost to friction in the same manner as kinetic energy, indicating confusion about the relationship between momentum and friction.
  • It is noted that while friction changes the momentum of the ball, Newton's 3rd law implies that momentum is conserved overall, with potential minor losses attributed to interactions with the ground or air.
  • One participant emphasizes that momentum is always conserved in any type of collision, countering the idea that it could be lost to friction.

Areas of Agreement / Disagreement

Participants express differing views on the conservation of momentum in relation to friction, with some asserting that momentum is conserved while others question how it is affected by friction. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are unresolved assumptions regarding the definitions of momentum and friction, as well as the implications of Newton's laws in this context. The discussion does not clarify the extent of momentum loss, if any, in practical scenarios.

member 529879
If a heavy ball is rolling on a surface, it eventually stops due to the frictional force. Where does the momentum of that ball go? Is it lost to heat, or does it maybe cause the Earth to move a very small and unnoticeable amount?
 
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It causes the Earth to move a very small and unnoticeable amount. But you had to have moved the Earth a small and unnoticeable amount when you started the ball rolling so, this should just cancel that out roughly (the center of mass has shifted by a little bit in the process).
 
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So is momentum not lost to friction in the same way that kinetic energy is?
 
Scheuerf said:
So is momentum not lost to friction in the same way that kinetic energy is?

Friction is a force and as such changes the momentum of the ball. But Newton's 3rd law says every force has an equal and opposite reaction force so that momentum is conserved. You could perhaps lose a little bit of momentum to pieces of the ground chipping or to the surrounding air or something, but you would probably just lump those elements together into "Earth".
 
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Scheuerf said:
So is momentum not lost to friction in the same way that kinetic energy is?

No. Momentum is always conserved in any type of collision.
 

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