# What does "stationary charges" mean in Coulomb's law?

• Amio C
In summary, the conversation discusses the concept of stationary charges in Coulomb's law and its implications. It is clarified that stationary charges mean they are not moving with respect to each other and the observer applying the law. If charges are in motion, Maxwell's equations must be used instead. Additionally, it is noted that in some cases, electrostatics can still be applied even with small velocities.
Amio C
Hello. I am an intro Physics student and this is my first post here.

In Coulomb's law the charges are said to be stationary. I need some clarification about what does it mean for two charges to be stationary:

A. Does it mean that the charges are not moving with respect to each other? (But maybe can move together with a constant velocity?)
B. Does it mean that the charges and the observer applying Coulomb's law has no movement compared to each other?
C. What if the charges and the observer all are accelerating at the same rate?

I am sorry if the answer is obvious. I would really appreciate your help.

Last edited by a moderator:
B. If the charges move you are no longer dealing with electrostatics and you will need the full set of Maxwell's equations to describe the electric and magnetic fields.

Amio C
Orodruin said:
B. If the charges move you are no longer dealing with electrostatics and you will need the full set of Maxwell's equations to describe the electric and magnetic fields.
So if two charges along with an observer (let's call him / her "X") is moving at a constant velocity and another observer ("Y") is not moving; then "X" can apply Coulomb's law but "Y" can not - am I correct?

Amio C said:
So if two charges along with an observer (let's call him / her "X") is moving at a constant velocity and another observer ("Y") is not moving; then "X" can apply Coulomb's law but "Y" can not - am I correct?

Yes - and of course this situation is equivalent to X and the two charges being at rest while Y is moving.

Amio C
Thanks to both of you. I understand it now.

This being said, it should be noted that in many of the cases you might deal with, velocities will be so small that you can apply electrostatics to a very good approximation.

Amio C

## What does "stationary charges" mean in Coulomb's law?

"Stationary charges" refers to the assumption that the charges involved in Coulomb's law are not moving. This means that the distance between the charges remains constant throughout the calculation.

## Why is the assumption of stationary charges important in Coulomb's law?

The assumption of stationary charges is important because it simplifies the calculation and allows for a more accurate result. If the charges were moving, the distance between them would constantly change, making the calculation more complicated.

## Can Coulomb's law be applied to moving charges?

No, Coulomb's law is specifically designed to calculate the force between stationary charges. It does not take into account the effects of moving charges.

## What is the difference between stationary charges and static charges?

Stationary charges refer to charges that are not moving, while static charges refer to charges that are at rest or not moving at the moment. Both terms can be used interchangeably in the context of Coulomb's law.

## Does the distance between stationary charges affect the force calculated by Coulomb's law?

Yes, according to Coulomb's law, the force between stationary charges is inversely proportional to the square of the distance between them. This means that the force increases as the distance between the charges decreases, and vice versa.

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