Does two dimensional motion imply conservation of angular momentum?

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Discussion Overview

The discussion revolves around the conservation of angular momentum in a system involving a particle attached to four springs, with motion constrained to the xy plane. Participants explore the implications of two-dimensional motion on angular momentum conservation, considering factors such as external torque and system boundaries.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant inquires whether angular momentum is conserved in a system with a particle and springs on the xy plane.
  • Another participant states that momentum is conserved only if there is no external torque, suggesting that the configuration of multiple springs may introduce torque.
  • A different viewpoint clarifies that while the angular momentum vector is perpendicular to the plane of motion, the existence of a third dimension is not negated by the two-dimensional nature of the motion.
  • One participant acknowledges the orthogonality of angular momentum to the plane but seeks to determine if it remains constant.
  • Another participant argues that angular momentum is not generally conserved if the springs are fixed, as this introduces external torque, contrasting with scenarios where the system is closed.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which angular momentum is conserved, indicating that the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

The discussion highlights the dependence on system configuration, such as whether springs are fixed or attached to movable objects, and the implications for external torque on angular momentum conservation.

anamariann123
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Hello!

I have a system composed by a particle attached to four springs that lie on the xy plane. The motion of the particle occurs on the xy plane. I wanted to know if the angular momentum is conserved. Thanks for your help :)
 
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Momentum is conserved if there is no external torque. If you have multiple springs going to a point, you probably have some torque on that point.
 
Perhaps you are thinking "the angular momentum vector is perpendicular to the plane of motion. Since this is two dimensional, there cannot be such a vector." That is mistaken. The fact that motion is "two dimensional" means that the motion occurs in two dimensions. It does not mean there is NO third dimension.
 
I know the angular momentum is orthogonal to the plane of motion, but I would like to know if it is constant.
 
Not in general, no. If the springs were attached to other objects that are free to move, it would be, because that would be a closed system. But if springs are attached to fixed points, it's the same as supplying external torque, so angular momentum will not be conserved.
 

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