Scalar potential in EM and Newton's Law

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Discussion Overview

The discussion revolves around the relationship between scalar potentials in electromagnetism and Newton's law of gravitation. Participants explore how the gradient of a scalar field relates to electric and gravitational fields and forces, examining the underlying principles and equations governing these concepts.

Discussion Character

  • Conceptual clarification, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions how the gradient of a scalar potential can yield both a field and a force, seeking clarification on the relationship between the two concepts.
  • Another participant suggests that the electric field can be viewed as a force scaled by charge, drawing a parallel to gravitational fields and weight.
  • A later reply confirms that the electric force can be expressed as -grad psi, equating it to the electric field E, and similarly for gravitational fields and forces.
  • Participants provide specific examples of scalar potentials for electric and gravitational forces, indicating that certain forms of U and psi lead to the respective forces and fields.

Areas of Agreement / Disagreement

Participants generally agree on the mathematical relationships between scalar potentials and their corresponding fields and forces, but there is some uncertainty regarding the initial understanding of these concepts.

Contextual Notes

Some assumptions about the definitions of scalar potentials and their applications in different contexts may not be fully articulated, and the discussion does not resolve all nuances of the relationships presented.

Who May Find This Useful

This discussion may be useful for students and enthusiasts of physics, particularly those interested in electromagnetism and classical mechanics, as well as those seeking to understand the mathematical relationships between forces and fields.

luxiaolei
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Hi,all, problem is:

in Electromagnetism, we introduced a scalar potential psi, such that:

E = - grad Psi

and In Newton's law, there is also a scar potential U, such that:

F= -grad U

My question is, one is the gradient of a scalar field give a field and a force?!

Can anyone help me with understanding this? That would be great, and many thanks in advance!
 
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The field is just a force scaled by charge. It is the same relationship as e.g. the gravitational field and weight.
 
DaleSpam said:
The field is just a force scaled by charge. It is the same relationship as e.g. the gravitational field and weight.

@DaleSpam; thanks for replay. I am very interested in your answer, however, I am not quite understood it. Would you explain it more? thanks

Can I say,

Electric force = -grad psi = E

or

Gravitation field = -grad U = F

if they are the same.
 
Yes. For example, if U = kCc/r then you get the electric force, if psi = kC/r then you get the electric field. Similarly, if U = GMm/r you get the gravitational force, if psi = GM/r then you get the gravitational field.
 
DaleSpam said:
Yes. For example, if U = kCc/r then you get the electric force, if psi = kC/r then you get the electric field. Similarly, if U = GMm/r you get the gravitational force, if psi = GM/r then you get the gravitational field.

Thanks a lot! Cleared my mind!
 

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