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Offline thebrain13

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« on: 31/10/2007 18:24:38 »
how do accelerating charges interact with one another?


 

Offline Soul Surfer

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« Reply #1 on: 31/10/2007 22:47:18 »
That isn't a simple question because the precise behaviour depends on a range of things like what sort of charges you are talking about ie whether the conditions are classical or quantum mechanical  what the velocities of the charges are the geometry of the interaction. and the reason why the charges are accelerating.

The cop out answer is that they interact acording to the normal rules of dynamics, Maxwells equations, relativity and quantum mechanics.

Please be more specific about the conditions and the deeper reasons for asking the question.
 

Offline thebrain13

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« Reply #2 on: 01/11/2007 02:58:43 »
I hear ya soul surfer, I was hopin somebody would just answer, even though I knew there was no way somebody would. I was feelin a bit lazy, I didnt want to explain a big thought experiment like I always do, but I guess I will afterall.

The deeper meaning, is a possible pattern between gravity and electromagnetism, as I was trying to figure out my unanswered post about g.r. And I want to know more about acceleration and its relationship with electric charge in general.

So tell me how this would work. What if you had two oppositely charged balls, one was orbiting around the other in outer space. Would the force between the two be bigger, smaller or equal to the force they would experience if they were stationary relative to each other?

Here is another experiment, what if you had two oppositely charged balls bouncing back and forth in a way that they were always traveling in opposite directions relative to the apparatus. They were seperated by a straight wall that keeps them from running into each other and also acts as a scale. Would their relative motion create a magnetic field increasing their attraction to one another? Or would the fact that they keep on accelerating in opposite directions nullify the affect?

And for my third experiment, what if you had two positively charged rocket ships that were accelerating toward one another, would their repulsive force be affected? Or would their repulsion only be based upon their initial strength of charge and their relative velocity?
 

Offline Soul Surfer

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« Reply #3 on: 01/11/2007 19:39:52 »
The following are just quick responses off the top of my head and have not been checked in detail.

Two orbiting balls 
assuming
1. large ie no Quantum considerations
2. slow  ie non relatavistic

The basic attractive force is not affected by the acceleration associated with the orbiting but there are I think two significant secondary forces. Firstly there is an energy loss due to the generation of electromagnetic radiation.  Secondly  the revolving charged bodies create a static magnetic field unless the charges are absolutely equal and opposite and  as they move in this field this will cause the axis of rotation to precess.

The second experiment is non physical and not realisable unless you attach the balls to stiff rods and move them about (or use rockets as in q3 ) the device would create an oscillating magnetic field and therefore radiate electromagnetic radiation.  The magnetic field would increase the attraction between the balls.  This is an example of the electromagnetic pinch effect seen in thunderballs where the discharge collapses into thin threads.

The third question is similar to the second except that the two balls have the same charge in this case the magnetic fields generated are opposing and the repulsive force increased.
 

Offline thebrain13

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« Reply #4 on: 01/11/2007 23:24:15 »
thanks soulsurfer, but boy, you sure made things a lot more complicated. Could you be a bit more specific on the nature of the electromagnetic radiation?
 

Offline ageon

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« Reply #5 on: 02/11/2007 00:54:07 »
Hi.
I suggest you look up the work of Walther Ritz who proposed (to put it in modern terms) that gravitational attraction was an outcome of small asymmetries in the electric interactions between protons and orbitting electrons basically caused by the fact that in atoms the electrons are moving around whereas protons are not.
 

Offline thebrain13

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« Reply #6 on: 02/11/2007 17:43:01 »
Consider this simultaneity experiment. you have three separate objects in a straight line. the object in the middle is a receiver and the objects to the outside of it are light emitters that flash little beacons of light at precisely the same time.(the flashes of light are simultaneous events) And lets say you are the observer and you are traveling towards the apparatus in line with the emitters and the receiver. One emitter is closer to you than the other. The one that is closer is called emitter a and the one that is farther is called emitter b.

Now, if you were traveling away from the apparatus you would view emitter a as firing first. Thats because the speed of light is constant and in order for the two beams to reach the center at the same time, emitter a would have to fire first, giving the beam a head start.

However, acceleration re-orders simultaneity. Lets say you were traveling away from the apparatus and you waited for both beams to be emitted. Depending on your speed, beam a might be half way there by the time beam b is emitted. But lets say you stopped moving right after they were both emitted at different times. If they maintained their constant velocity(c)relative to you beam a would reach the center first. This can not be the case. So what happens?

Well in order for the speed of light to remain constant, and for the rules of simultaneity to not create any paradoxes, the geometry of space must change for accelerating observers. More specifically, space in front of an accelerating object is condensed, and space behind an accelerating object is more spread out. Also space gets more and more condensed the farther in front of an accelerating object it is, and consequently more and more spread out the farther behind you are. The severity of the affect is based on distance, and your acceleration.

So this resolves the paradox between simultaneity and the constancy of the speed of light in my experiment, because even though light in beam a got a head start, it didn't have to travel as far, in the observers frame of reference due to the acceleration.

Now that resolves that paradox just fine, but it leads me to another question. If acceleration condenses space in front of the object, why wouldn't that object view an increase in the strength of electrical charge in the condensed space? (since there is more of that charge in that area)
 

Offline thebrain13

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« Reply #7 on: 06/11/2007 20:24:54 »
Do you guys understand what Im saying? Was that clear enough?
 

Offline JP

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« Reply #8 on: 07/11/2007 18:25:26 »
I wasn't going to jump in since I'm no expert in general relativity, but I can try to answer it.  There's a couple of points to be made here:

1) Gravity won't affect charge itself.  If you put an electron (-e charge) in a gravitational field, its charge is still -e.

2) Charge generally comes smeared out over some object.  For example, you could have a balloon with a charge -100e on it (100 electrons are smeared over it).  If you put this balloon in "compressed space" it would get compressed along with the space it occupies, changing its shape, but the total charge would not change.  The only difference is that when you calculated the field generated by the balloon, you have to take into account the curvature of the space. 
 

Offline thebrain13

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« Reply #9 on: 21/11/2007 18:15:13 »
sorray if I bring up older topics but I noticed something.

"Gravity wont affect charge itself"

Are you sure about that? Gravity redshifts photons if they move up the gravitational potential, and they blueshift photons when they move down. If photons are the mediators of electric force, then gravity does affect electric force.

And of course given the equivalence principle, if gravity affects electric force, so does acceleration.
 

Offline JP

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« Reply #10 on: 22/11/2007 02:51:24 »
Gravity should affect the electromagnetic force since we know that accelerating particles will emit different fields than stationary particles (then you can apply the equivalence principle to relate acceleration and gravity). 

However, you can affect the fields generated by a particle without affecting the particle itself.  For example, if you throw a rubber ducky in a bathtub full of still water, it will make some waves.  Now, if you throw the same rubber ducky into a bathtub after you pull the plug out of the drain, the waves will be a different shape.  You still have the same rubber ducky (which is like the charge), but the waves it generates are different shapes because you're changing the properties of the water (which is like space being warped in general relativity). 
 

Offline thebrain13

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« Reply #11 on: 25/11/2007 07:12:41 »
"gravity should affect the electromagnetic force since we know that accelerating particles will emit different fields than stationary particles."

Explain what you mean by an accelerating object emits a different field?

I thought we had established that acceleration does not affect an electromagnetic field.
 

Offline thebrain13

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« Reply #12 on: 28/11/2007 23:07:37 »
Okay, Ill ask this question. If a photon that travels down a gravitational potential gains energy, and a photon that travels up a gravitational field loses energy, than two equally charged objects one placed on top of the other, would experience a net downward force. Why doesn't that happen, what am I missing?
 

Offline JP

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« Reply #13 on: 29/11/2007 00:08:24 »
Explain what you mean by an accelerating object emits a different field?

I thought we had established that acceleration does not affect an electromagnetic field.

This is all classical electrodynamics here, no general relativity:

1) Acceleration doesn't affect the charge of a particle. 
2) Acceleration does cause a particle to radiate a field that is different from if that particle were stationary or moving at a constant velocity. (http://en.wikipedia.org/wiki/Bremstrahlung)  The details are really hard to calculate.

Quote
Okay, Ill ask this question. If a photon that travels down a gravitational potential gains energy, and a photon that travels up a gravitational field loses energy, than two equally charged objects one placed on top of the other, would experience a net downward force. Why doesn't that happen, what am I missing?
You've lost me here.
 

Offline thebrain13

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« Reply #14 on: 29/11/2007 17:12:05 »
If two like charges, were stacked one on top of the other in a gravitational field, the top object would push the bottom one down harder the the bottom one pushes the top. Thats because when a photon travels up a gravitational field it is redshifted, and when it moves down it is blue shifted.

Why doesnt that happen?
 

Offline JP

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« Reply #15 on: 29/11/2007 18:06:52 »
I think it does happen.  The calculations are beyond anything I can manage, but if, for example, you send one particle into a black hole, photons could go one way (from outside the black hole to inside of it), but not the other way (since they can't escape the black hole). 

What I've been saying is that both particles would still have the same charge, no matter where you put them.  The fields they emit will certainly be affected if we accelerate them (this has been observed experimentally).  If that's the case, then equivalence should state that the fields they emit will end up being distorted by gravity, which is probably what's showing up in the red shift/blue shift.
 

Offline thebrain13

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« Reply #16 on: 30/11/2007 18:59:47 »
If that were the case, then objects with lots of charge, would fall faster than neutrally charged objects.

Does that happen?
 

Offline JP

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« Reply #17 on: 30/11/2007 20:38:10 »
Wouldn't it end up falling slower?  If an accelerating charged particle gives off radiation, that radiation would carry away energy and therefore the particle would have to slow down.  A neutral particle wouldn't have that problem. 
 

Offline thebrain13

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« Reply #18 on: 30/11/2007 20:53:57 »
I wasnt talking about individual particles. I was talking about groups of particles. If there was a group of positively charged particles in a gravitational field, the particles that emitted photons on the top that traveled down to the bottom would push harder than the particles that emitted photons on the bottom and then traveled upwards, due to gravitational redshift/blueshift affect.
 

Offline JP

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« Reply #19 on: 04/12/2007 17:58:57 »
I'll admit, you have me stumped.  The problem with dealing with photons in terms of general relativity is that the model which gives photons does not, to the best of my knowledge, account for general relativity.  When you deal with things that small, you probably have to start considering quantum theories of gravity.
 

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« Reply #19 on: 04/12/2007 17:58:57 »

 

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