Coulomb's law, electrostatics?

[Jurtinus]

Those are the SOURCE charges. They are the two charges on the two ends. The TEST charges is the one in the middle, because that is the charge where you are calculating the force for!

The two source charges are NOT MOVING, resulting in electric field that is STATIC WITH TIME atthe middle test charge. The middle test charge still has a NET FORCE. Nothing is moving with respect to time in that problem.

When will this sink in?

Zz.

New to PF, not sure if you've been notified. Check above.

 

[Dale]

Dale: I'm unsure wether your reply would change.

Yes, it does change. The additional information clearly specifies that the charges are at fixed locations.
Coulomb’s law clearly applies as specified.

The FBD seems incomplete.

 

[Herman Trivilino]

There is a net force, the particle isn't in equilibrium.

True.

1) How can there be a net force if the particle is in equilibrium?

The particle is not in equilibrium.

2) If the particle is not in equilibrium, how does Coulombs law apply?

Because the particles are not moving.

 

[Jurtinus]

Yes, it does change. The additional information clearly specifies that the charges are at fixed locations.
Coulomb’s law clearly applies as specified.

The FBD seems incomplete.

What if it is not. Could Coulombs Law alone suggest the impending motion of a particle at an instant, without the need of additional conditions? Such as Coulombs dry friction, covered in engineering statics.

Thanks:)

 

[ZapperZ]

ZapperZ: My mistake aside, from the FBD alone, the particle would have to be in motion or impending motion. This is where you lose me.

Thanks again:)
Sorry for the mistake:(

The FBD has nothing to do with the particle being in motion or not. The FBD shows the forces acting on the particle at that particular instant at that particular location.

If you let the situation continues, then the particle will move, and now, we no longer have the same situation as before because at a different location, the forces will be different. Furthermore, a moving change in a changing electric field (the electric field can be different at different locations) has other complications added to it that is NOT covered here.

You will deal with uniform electric field soon enough, and you'll see the case of charged particle moving in such a field. In that case, then you have the same kinematical equation that you had when dealing with particles in a uniform gravitational field.

Zz.

 

[ZapperZ]

What if it is not. Could Coulombs Law alone suggest the impending motion of a particle at an instant, without the need of additional conditions? Such as Coulombs dry friction, covered in engineering statics.

Thanks:)

What if it is? Aren't you trying to make this more complicated than it is, and adding stuff to something you had just barely learned? Look further into your textbook. There's a LOT more in classical E&M than what you know right now. You haven't done anything to account for time-varying effects, and the added complications there may make you regret that you will have to consider such effects.

Be careful what you ask for, because you might just get it!

Zz.

 

[Dale]

Could Coulombs Law alone suggest the impending motion of a particle at an instant, without the need of additional conditions?

Yes, If by “impending motion” you mean “acceleration”. For this specific problem Coulomb’s law holds even if the FBD is complete.

 

[Jurtinus]

What if it is? Aren't you trying to make this more complicated than it is, and adding stuff to something you had just barely learned? Look further into your textbook. There's a LOT more in classical E&M than what you know right now. You haven't done anything to account for time-varying effects, and the added complications there may make you regret that you will have to consider such effects.

Be careful what you ask for, because you might just get it!

Zz.

The things I discuss here are things I wonder about. I come to this forum in search of enlightenment. There is not enough time nor care at school to ponder these things with fellow peers and professors. I hope, one day, you find the curiosity of other humans inspiring Zz. Please, refrain from patronizing.

I have strenuously attempted to read derivations (among others) of the magnetic field in the past. I’ll tell you about my right hand. As I punch myself in the face with it.

Thanks:/

 

[Jurtinus]

Yes, If by “impending motion” you mean “acceleration”. For this specific problem Coulomb’s law holds even if the FBD is complete.

Impending, as in; “about to happen.”

Although, I think your catching my drift. In which case, you have answered my inquiry.

Thanks:)

 

[ZapperZ]

The things I discuss here are things I wonder about. I come to this forum in search of enlightenment. There is not enough time nor care at school to ponder these things with fellow peers and professors. I hope, one day, you find the curiosity of other humans inspiring Zz. Please, refrain from patronizing.

I encourage curiosity all the time! It is part of my job, and all the students that I mentor hear this from me often!

But what you asked was not "curiosity", especially when you've been told that you're applying a wrong set of rules and criteria taken from somewhere else! I've spent time and effort trying to correct that, and at some point, when I have to keep repeating the same thing over and over again, even you should understand how frustrating it can get!

Like I have said, look further into your text. And if you're curious enough, look at what we call as Maxwell equations. Your E&M lessons are all leading up to them and the Lorentz force law. I show my students Maxwell equations and the Lorentz force law on the very first day and explicitly tell that everything they are about to learn in E&M is aimed towards finally understanding all those equations. So if you are that curious, go look it up!

Zz.

 

[Dale]

Impending, as in; “about to happen”

Well then that is wrong. Coulomb’s law (plus Newton’s 2nd law and any other applicable force laws) at time t=t0 tell you the acceleration at time t=t0. They do not tell you the motion at time t>t0. They tell you about “instantaneous acceleration” not “impending motion”.

 

[Jurtinus]

Well then that is wrong. Coulomb’s law (plus Newton’s 2nd law and any other applicable force laws) at time t=t0 tell you the acceleration at time t=t0. They do not tell you the motion at time t>t0. They tell you about “instantaneous acceleration” not “impending motion”.

Then, I must conclude, Coulombs Law cannot suggest impending motion. At least, not without additional conditions.

Thanks:)

 

[Jurtinus]

I encourage curiosity all the time! It is part of my job, and all the students that I mentor hear this from me often!

But what you asked was not "curiosity", especially when you've been told that you're applying a wrong set of rules and criteria taken from somewhere else! I've spent time and effort trying to correct that, and at some point, when I have to keep repeating the same thing over and over again, even you should understand how frustrating it can get!

Like I have said, look further into your text. And if you're curious enough, look at what we call as Maxwell equations. Your E&M lessons are all leading up to them and the Lorentz force law. I show my students Maxwell equations and the Lorentz force law on the very first day and explicitly tell that everything they are about to learn in E&M is aimed towards finally understanding all those equations. So if you are that curious, go look it up!

Zz.

I do understand your frustration, and I appreciate all your (and everyone’s) effort. Usually, I have to beat my head against a wall to understand something completely.

However, I think my approach was appropriate. I stuck to the laws and definitions, while trying to see what I can squeeze out of them. Nonetheless, wisdom is a maturation process. The same definitions, will have the same form, but will become to mean something else.

Thanks Zz:)

P. S. I will take a peak at Maxwell’s equations.