Can potential energy be negative at infinity?

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Discussion Overview

The discussion revolves around the concept of potential energy, particularly whether it can be negative at infinity, and how it relates to atomic binding and forces such as gravity and magnetism. Participants explore the implications of setting potential energy to zero at infinity and the conditions under which potential energy can be negative.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that potential energy can take on negative values due to the arbitrary nature of the integration constant in its formula, emphasizing the importance of differences in potential energy (ΔU) rather than absolute values.
  • It is noted that when attractive forces are involved, such as gravity or Coulomb forces, and the displacement is towards the center of the field, the change in potential energy (ΔU) is negative, indicating a release of energy.
  • Conversely, when displacement is away from the center of the field, ΔU is positive, requiring energy input to separate the objects.
  • In repulsive force fields, the relationship is reversed, with ΔU being negative when moving apart and positive when coming together.
  • One participant questions how to define a body as being out of a magnetic field in terms of potential energy, suggesting that stating the potential is zero can be misleading.
  • Another participant suggests setting the potential energy to zero at infinity as a solution to the ambiguity regarding potential energy values.
  • Further clarification is provided on the meaning of "zero at infinity," explaining that it refers to the limit where potential energy approaches zero as distance from a chosen origin increases indefinitely.
  • There is mention of the complexity involved in applying this concept to magnetic potential energy due to additional factors like the angle of the dipole.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the interpretation of potential energy at infinity and the implications of setting it to zero. The discussion remains unresolved, with no consensus on the best approach to defining potential energy in various contexts.

Contextual Notes

Limitations include the dependence on the choice of reference points for potential energy and the unresolved nature of how to accurately describe a body’s position relative to a magnetic field in terms of potential energy.

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When can the potential be in a negative value especially when it come to atoms and bind formation?
 
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Potential energy can have negative value whenever you like, since the formula includes the integration constant that can be set to an arbitrary value. That's why we usually only concern ourselves with the difference between potential energies at some two points in the field(ΔU).

If you want to know when is the difference in PE negative, then it depends on the direction of the force and the direction of displacement.

When the force is attractive, like with gravity, strong nuclear force, or Coulomb force for odd charges, AND the displacement is towards the centre of the field, then the ΔU is negative. Meaning, there is a release of energy as the objects comprising the system get closer.
If the displacement is away from the centre of the field, the ΔU is positive - it requires input of energy to move the objects apart.

In a repulsive force field(e.g., like charges repelling) it is the other way around.
 
Bandersnatch said:
Potential energy can have negative value whenever you like, since the formula includes the integration constant that can be set to an arbitrary value. That's why we usually only concern ourselves with the difference between potential energies at some two points in the field(ΔU).
If you want to know when is the difference in PE negative, then it depends on the direction of the force and the direction of displacement.
When the force is attractive, like with gravity, strong nuclear force, or Coulomb force for odd charges, AND the displacement is towards the centre of the field, then the ΔU is negative. Meaning, there is a release of energy as the objects comprising the system get closer.

If the displacement is away from the centre of the field, the ΔU is positive - it requires input of energy to move the objects apart.
In a repulsive force field(e.g., like charges repelling) it is the other way around.
Yeah yeah I got your point that potential energy is an arbitrary value, but but if we consider a metal is out of a Magnet's magnetic field it's potential should be zero but saying the potential is zero is a little bit misleading as it could be in the field and it's potential is still zero as it's an arbitrary value, how can I precisely say that the body is out of the field in terms of potential energy ?
 
Just set the potential energy to be zero at infinity.
 
Bandersnatch said:
Just set the potential energy to be zero at infinity.
What is meant by zero at infinity ?
 
ElmorshedyDr said:
What is meant by zero at infinity ?

Rigorously, this means that one sets the integral used to define potential energy equal to zero at the limit as distance from some chosen origin goes to infinity. I think the simplest example is gravitational potential energy. Have you taken calculus? You don't really need calculus to get this idea, but the argument is a bit more "hand-wavey". Using gravity, you can find a value for ##r## that will make the potential energy arbitrarily close to 0. You just need to choose larger and larger values of ##r##. In the limit, one says that the potential energy is "zero at infinity" to mean that one can make the potential arbitrarily close to zero by taking a larger ##r##.

You can apply the same idea to magnetic potential energy, but it is a bit trickier because the angle of the dipole also matters.
 

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