Lorentz force

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prosilio
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Lorentz force

Postby prosilio » Tue Feb 26, 2019 7:12 pm UTC

Hello.
I would appreciate opinions on the following issue.
I was contemplating the idea of using the lorentz force as a driving force. So please consider the following arrangement:
Let's assume we have a chassis placed on rails and that it can move on them without friction.
On it we place helmholtz coils that produce a uniform magnetic field between them.
Right in the middle of the helmholtz coils we place a cable in a perpendicular direction in regards to the rails.
When we provide current to the circuit, a lorentz force is exerted on the cable from the helmholtz magnetic field.

Do you think this arrangement would result in moving the chassis along the rails or am I missing something?
Thanks in advance!

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Soupspoon
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Re: Lorentz force

Postby Soupspoon » Tue Feb 26, 2019 9:08 pm UTC

What's attached to what, exactly? By my first reading, you're trying to get either the coils to get a force from the perpendicular cable or vice-versa, when both must be true.

If coil and perpendicular are both on the bogey, they aren't pushing it anywhere by their interaction. If you've got one of them on the track then it's a version of the classic linear motor but with the small technical problem of how the coil pair(s) pass across the perpendicular(s) for any significant untethered distance.

Or I've got the wrong image of your suggestion. (Cue me contorting fingers into Left Hand Rule/Right Hand Grip Rule formations to juggle my mental images accordingly.)

KittenKaboodle
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Re: Lorentz force

Postby KittenKaboodle » Tue Feb 26, 2019 10:07 pm UTC

prosilio wrote:Hello.
I would appreciate opinions on the following issue.
I was contemplating the idea of using the lorentz force as a driving force. So please consider the following arrangement:
Let's assume we have a chassis placed on rails and that it can move on them without friction.
On it we place helmholtz coils that produce a uniform magnetic field between them.
Right in the middle of the helmholtz coils we place a cable in a perpendicular direction in regards to the rails.
When we provide current to the circuit, a lorentz force is exerted on the cable from the helmholtz magnetic field.

Do you think this arrangement would result in moving the chassis along the rails or am I missing something?
Thanks in advance!


Umm, Newton's third law?
Perhaps I'm being a bit snarky as it is not entirely clear what the orientation of your coils are, I suppose it is possible that the "equal and opposite force" is perpendicular the rails, not along the rails, but that is just engineering not "science"

If you have a way to support something without friction I'd forget the Helmholtz coils and contact a patent attorney. https://www.xkcd.com/669/

Oh, I see Soupspoon has brought up something I hadn't considered, I just assumed the wire was independent of the chassis. I hadn't even considered the possibility that you are trying to make a "space drive". Now, I realize you don't know what you don't know, and there is some risk in dismissing an idea just because "if it was that simple someone would already have done it" but in this case that would be pretty reasonable, because enough people have been trying long enough that a LOT of things have been tried and universally failed(except, perhaps, some tiny effects right on the bleeding edge of experiment design). Now one might think that there is something magical about Helmholtz coils, but one would be wrong if one expects that magic to override well excepted "laws"

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Soupspoon
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Re: Lorentz force

Postby Soupspoon » Tue Feb 26, 2019 11:27 pm UTC

The only way I could make it work is to have the coils in the horizontal plane (axially vertical, OP never having ruled that out) so that the current through the perpendicular (horizontal) wire passing across the gap would push along the rails.

Except that the coil separation would need to be held open by something that doesn't impede/get-impeded-by the perpendicular wire (with wire trackside and coil on the trolley, or vice-versa), which is a worrying technical problem.

If I'm not making a stupid mistake about current/field/force directions, though, it occurred to me that a zig-zagged wire (criss-crossing, maybe more like a square-wave than a triangular one, but with criss-to-cross distance a tad greater than the circumference of the coils) could be held at one side and the coils held apart on the opposite side as if a no-contact clamp. Then as the train coils moves along 'around' the zig-zag (or the train zig-zag moves through each primary trackside coil) switch the current into reverse (in either wire or coil, whichever is easier) to obtain the 'return zag' force in the same direction as just abandoned.


Or why have the paired coils, anyway? A singular coil (or slightly beyond one end of a helmholtz pair) still has a field. Non-uniform, perhaps less efficient, but a wire passed across the end (with neither wire nor coil(s) structure needing to intersect the structure of the counterpart) should by feasible and can be mounted ventrally/dorsally without having to hold (out) to the side(s).

But I don't see the advantages over other more traditional linear motor (or railgun?) configurations of currents and fields making motion. Maybe it's good for something I'm not thinking of?


Or maybe OP is thinking Space Drive, and I'm overthinking something completely different!

prosilio
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Re: Lorentz force

Postby prosilio » Wed Feb 27, 2019 3:32 pm UTC

Firstly, thank you all for bothering to reply!
Secondly, I'm sorry I was not very exact at describing the arrangement! Give me one more chance.
So, I would like to clarify a few things.
The helmholtz coils and the cable are fixed on the chassis. The chassis is free to move along the rails.
The helmholtz coils are placed on top of each other and the cable is lying right in the middle of them.
Also, the cable is perpendicular to the rails.
The helmholtz magnetic field exerts a lorentz force on the cable and the cable's magnetic field exerts a lorentz force on the coils.
It's easy to say that due to newton's action-reaction principle these forces are cancelled, but are they?
Have you ever made the math?
I did and I don't think cancel each other, unless I'm wrong of course!
Since I can't build a miniature setup to test the above I came here asking you.
So, what do you think?

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Eebster the Great
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Re: Lorentz force

Postby Eebster the Great » Wed Feb 27, 2019 4:50 pm UTC

What is pushing against what here? Is the cable attached to anything?

As I understand it, you have a cart moving along a straight, level, two-rail train track. On the cart, you have magnets set up in some way such that the magnetic force on a wire running left-to-right pushes the wire forward. This makes sense. What I don't understand is how pushing this wire is supposed to push the cart. Is the wire attached to the ground, allowing the cart to push off the Earth? If the wire is just part of the cart, then it is only pushing off itself. It's like pulling yourself out of a swamp by your own hair. Of course the forces have to cancel in that case; otherwise it would violate conservation of momentum, conservation of energy, Newton's third law, and Maxwell's equations.

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Soupspoon
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Re: Lorentz force

Postby Soupspoon » Wed Feb 27, 2019 5:51 pm UTC

Looks like my "only way to make it work" setup was as you describe, OP, except that you're making the classic Perpetual Motion Engine errors.

prosilio wrote:The helmholtz magnetic field exerts a lorentz force on the cable and the cable's magnetic field exerts a lorentz force on the coils.
It's easy to say that due to newton's action-reaction principle these forces are cancelled, but are they?
Have you ever made the math?
I did and I don't think cancel each other, unless I'm wrong of course!
Since I can't build a miniature setup to test the above I came here asking you.
So, what do you think?


Ignore exact magnetic field formulae, as they don't add anything at this point.

1) The coils exert a force on the wire can be summarised as FCoilsFieldOnWire + FCoilsFieldOnCoils = 0, because any force the coil applies on the wire is necessarily balanced by the counter-push back upon the coils.

2) The wire, in turn, exerts a force on the coils that can be summarised as FWireFieldOnCoils + FWireFieldOnWire = 0, because any force the wire applies on the coils is balanced by the counter-push back upon the wire.

3) It does not matter whether the absolute magnitude of either of the #1 Fs (just concerning the coil-derived lorentz force) matches the absolute magnitude (regardless of sign) of either of the #2 Fs (ditto but the wire-derived component), the force upon the wire is FCoilsFieldOnWire + FWireFieldOnWire, whether or not the two elements are equal, which you seem to be taking as possible.

4) Ditto FCoilsFieldOnCoils + FWireFieldOnCoils is the sum total coil-pushing force.

Now add #3 and #4 together, using #1 and #2 statements to simplify the terms. You will find that it resolves to zero, because #3 is the direct negation of #4. Regardless of whatever differences you perceive (also wrongly, I highly suspect, in this case) between the #1 magnitudes and the #2 ones according to your (mis?)understanding of the coil-lorentz and wire-lorentz equations of force.


If the coil and wire were separate (one on track and one on chassis) the #3 total and the difference (i.e. being the direct negation, so double the 'individual' components) against the #4 total moves the chassis. No problem there. So long as the wire remains in the same position within the coil, which it straight away won't because of the movement. But you're moving, and if you supply a newly-entering wire(s) further up then you can add more force as required (if you have to, in a system not devoid of friction or if you still need more acceleration). That's essentially a linear motor setup.

But you (definitely, now) have wire mounted on the chassis, along with the coils. The force applied to the coil tries to push the coil pushes the chassis pushes the wire, and the equal-but-opposite force applied to the wire tries to push the wire pushes the chassis pushes the coil in exact opposition, so nothing at all happens to the chassis+coils+wire that was not already happening to the setup beforehand. Q.E.D.

HTH, HAND…

KittenKaboodle
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Re: Lorentz force

Postby KittenKaboodle » Wed Feb 27, 2019 9:02 pm UTC

prosilio wrote:The helmholtz coils and the cable are fixed on the chassis.
...
Since I can't build a miniature setup to test the above I came here asking you.


A simple experiment requiring no special equipment that will demonstrate the general problem would be to reach down and grab your shoe laces (or bootstraps if you have boots with straps) and try to lift yourself off the ground.

Sure the details are not the same, but as I said before it would be a mistake to consider Helmholtz coils magical to an extent that would violate well established laws.

prosilio
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Re: Lorentz force

Postby prosilio » Thu Feb 28, 2019 5:42 pm UTC

KittenKaboodle wrote:
prosilio wrote:The helmholtz coils and the cable are fixed on the chassis.
...
Since I can't build a miniature setup to test the above I came here asking you.


A simple experiment requiring no special equipment that will demonstrate the general problem would be to reach down and grab your shoe laces (or bootstraps if you have boots with straps) and try to lift yourself off the ground.

Sure the details are not the same, but as I said before it would be a mistake to consider Helmholtz coils magical to an extent that would violate well established laws.


I was expecting that kind of ridiculous answers, but I was also hoping for more.
I specifically said that I'm aware that what I'm asking is going against Newton's law but is it?
I made the math and I think there is something to check. It's clear that you don't. So OK.

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Soupspoon
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Re: Lorentz force

Postby Soupspoon » Thu Feb 28, 2019 6:37 pm UTC

prosilio wrote:[I was expecting that kind of ridiculous answers, but I was also hoping for more.
Ridiculous? More? Please explain.

I specifically said that I'm aware that what I'm asking is going against Newton's law but is it?
It is, so what is your alternate thinking?

I made the math and I think there is something to check. It's clear that you don't. So OK.
If you made the math(s) then we obviously need to see what you see.

Did you have a problem with my basic treatment of the equality, for example? If not, what does your detail do to change it?

If you don't care to share it because you think it could compromise your shot at a Nobel Prize (or Fields Medal) to share anything, then you probably shouldn't have started this conversation with us knowing you'd say nothing of substance. We can help, otherwise. So far we've addressed what you gave us (evenif we had to guess bits) but if you have something of a deal-breaker then we'd appreciate seeing it to understand where you're actually coming from.

I, for one, look forward to learning something exciting.

prosilio
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Re: Lorentz force

Postby prosilio » Thu Feb 28, 2019 8:45 pm UTC

Soupspoon wrote:
prosilio wrote:[I was expecting that kind of ridiculous answers, but I was also hoping for more.
Ridiculous? More? Please explain.

I specifically said that I'm aware that what I'm asking is going against Newton's law but is it?
It is, so what is your alternate thinking?

I made the math and I think there is something to check. It's clear that you don't. So OK.
If you made the math(s) then we obviously need to see what you see.

Did you have a problem with my basic treatment of the equality, for example? If not, what does your detail do to change it?

If you don't care to share it because you think it could compromise your shot at a Nobel Prize (or Fields Medal) to share anything, then you probably shouldn't have started this conversation with us knowing you'd say nothing of substance. We can help, otherwise. So far we've addressed what you gave us (evenif we had to guess bits) but if you have something of a deal-breaker then we'd appreciate seeing it to understand where you're actually coming from.

I, for one, look forward to learning something exciting.


I will simply tell you that, as far as I know, it is not certain that Newton's Law on action-reaction is valid when it comes to electromagnetism.
And I don't need a nobel prize to know that!
Maybe you are right it was my mistake to open this post.
Consider it done.

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Soupspoon
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Re: Lorentz force

Postby Soupspoon » Thu Feb 28, 2019 9:04 pm UTC

prosilio wrote:I will simply tell you that, as far as I know, it is not certain that Newton's Law on action-reaction is valid when it comes to electromagnetism.
And I don't need a nobel prize to know that!

You intrigue me greatly. But you're going to leave me hanging, I presume.

(It's not something to do with Lorentz factors, is it? Is that your thinking?)

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Eebster the Great
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Re: Lorentz force

Postby Eebster the Great » Thu Feb 28, 2019 11:25 pm UTC

I assume you started this thread to discuss an idea, but the problem is that it isn't clear what your idea is yet and you won't accept the answers you've gotten based on what it appears to be. Maybe you could help fill in some details.

1. What are the required elements in your design, and how are they linked? For instance, what is connected to the cart, what is connected to the track, what is connected to each other, etc.
2. What principle of physics are you using? The "Lorentz force" is just the general electromagnetic force on a charged particle or current-carrying wire. You need to be more specific.
3. What makes you expect a surprising result? Newtonian mechanics with Maxwell's equations is the currently accepted model of classical electrodynamics. There must be a reason why you expect divergent behavior in this case.
4. How could we test your idea by building a real device? If it's impossible to build one, then you will need to explain why, but your design seems straightforward enough to build in the real world.

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Zamfir
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Re: Lorentz force

Postby Zamfir » Fri Mar 01, 2019 9:09 am UTC

prosilio, I have done the math on similar situations, and it does balance out if you do the math right. But you have to be careful.

For example, in your example you describe a "cable". Where is the return path for that current? Make sure that you calculate the force on the entire electric circuit, not just on one piece of the circuit

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Re: Lorentz force

Postby p1t1o » Fri Mar 01, 2019 10:32 am UTC

@prosilo
Dont take it personally, this is the internet. There are people around on the web that will argue to the death that 1*1 cannot equal 1 (Im serious. This is a real thing that some people believe) and that modern mathematics is a conspiracy.
So when people turn up questioning extremely well established physical law, its common for people to react with extreme caution and little patience.
Because the nutbars are far more common than people with honest questions like yourself.

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Sizik
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Re: Lorentz force

Postby Sizik » Fri Mar 01, 2019 1:04 pm UTC

Could you draw a picture?
she/they
gmalivuk wrote:
King Author wrote:If space (rather, distance) is an illusion, it'd be possible for one meta-me to experience both body's sensory inputs.
Yes. And if wishes were horses, wishing wells would fill up very quickly with drowned horses.

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Eebster the Great
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Re: Lorentz force

Postby Eebster the Great » Sat Mar 02, 2019 5:47 am UTC

p1t1o wrote:@prosilo
Dont take it personally, this is the internet. There are people around on the web that will argue to the death that 1*1 cannot equal 1 (Im serious. This is a real thing that some people believe) and that modern mathematics is a conspiracy.

Oh my God I just looked this up, and now I wish I hadn't.


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