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General discussionPhysic topic: The Lorentz force(21 posts)solved(21 posts)solved
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Posted February 08, 2015
I have "built" a couple of primitive electric motors working on the same principle as the first one by Faraday (as seen in many youtube videos). The thing is that I don't really understand how they work. I know intuitively that substituting a magnet for the wire won't work because that would break physic (by creating perpetual motion) but I can't say I really understand why or why not since the direct current going through the wire simply create a magnetic field.

I understand how conventional electrical motor works since they are simply about attraction and repulsion of magnetic poles but Faraday's motor does not work that way. It works using something called the Lorentz force. I've read a couple of explanation of it but I don't understand them. I have the feeling (that maybe wrong) that this might lead to me understanding radio waves and what make them different from induction.

I know from experience that not understanding an explanation does not mean I won't understand all explanations.

Please don't link to the Lorentz Force article on Wikipedia as it is one of the explanations I do not understand.
This question / problem has been solved by jdsgnimage
Posted February 08, 2015
Electricity isn't exactly my forte; but after some research it I will try to describe it.

The lorentz force is something which occurs when a conductor carrying an electric current is subjected to an external magnetic field.

For the motor you are building, the presence of the magnet causes a magnetic field which creates a lorentz force normal to the conductor. The force in that direction causes a torque around the rotational axis of the conductor which results in rotational motion of the motor.

I know you didn't want references to wikipedia but the "force on a current carry wire" subsection of the Lorentz Forces article is directly applicable to your question. You may also find the article on "homopolar motors" useful as well since it discusses exactly the kind of motor I think you are building..
Posted February 08, 2015
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dacolem1: I know you didn't want references to wikipedia but the "force on a current carry wire"
Looks like 80% college level math and although that might be useful to prove or explain something, it's probably unreadable to some of us, including me.
Posted February 08, 2015
From my limited knowledge is that Lorentz force is when there is a current flowing through a conductor there will be electromagnetism.
If you would look at a cutthrough of the conductor, if the current is going away from you, commonly marked with a cross, the force will rotate clockwise, if the current is coming toward you, commonly marked with a dot, it will rotate counterclockwise.
Now if you have a coil and make a cutthrough you can see how the fields rotate and what will be the north and south pole.
Posted February 09, 2015
A great resource to learn about this stuff: US Navy NEETS manuals.

http://jacquesricher.com/NEETS/

Not sure if it specifically mentions the Lorentz force by name but for certain you'll get your fill of AC and DC current theory, and motors.
Posted February 09, 2015
I'm a physicist. I'd love to be helpful here, but I'm not sure what you don't understand. To be honest, things are hard to explain in physics if one can't intuitively "get them".
Posted February 10, 2015
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sunshinecorp: I'm a physicist. I'd love to be helpful here, but I'm not sure what you don't understand. To be honest, things are hard to explain in physics if one can't intuitively "get them".
Sorry about not being clear, what I'm looking for is an intuitive explanation of why the force exist and why is it in the direction it is. I am not looking for methods to figure out its force and direction.

I think from my readings that I'll probably just have to accept that it is the way it is because of the electrical faery.
Posted February 10, 2015
This might help a little bit as a jumping-off point (paragraph 4 is the most relevant to what you're asking, I think).

http://www.scientificamerican.com/article/happy-birthday-electron/?page=1

Also:

[url=]https://answers.yahoo.com/question/index;_ylt=A0LEVr20KNpU22sA0cwnnIlQ?qid=20110719074944AA13iSf[/url]

https://www.physicsforums.com/threads/why-does-the-right-hand-rule-works.472162/

My takeaway from a quick read-through:

The right-hand rule and the Lorentz force law will accurately predict what the observer will observe.

The rules do not explain why magnetism exists.
Posted February 10, 2015
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sunshinecorp: I'm a physicist. I'd love to be helpful here, but I'm not sure what you don't understand. To be honest, things are hard to explain in physics if one can't intuitively "get them".
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justanoldgamer: Sorry about not being clear, what I'm looking for is an intuitive explanation of why the force exist and why is it in the direction it is. I am not looking for methods to figure out its force and direction.

I think from my readings that I'll probably just have to accept that it is the way it is because of the electrical faery.
You"ll problably have to dive into quantumphysics to get an answer to that. I also think the scientific community will be all ears to see with what you come up with and there may be a Nobelprize in it for you. :^)
Posted February 10, 2015
I just read the Wikipedia article and is very informative. I recommend to read it slower, as it has practical information (how to use it, which I already knew from my Physics lesons) and more theoretical parts. What you seem to be looking for, what I call the "epistemology" of the force, is way to complicated to understand without being deep into Physics. It reminds to me when I wanted to understand the law of Biot-Savart and not only know the math.
I copy from Wikipedia:
Using Heaviside's version of the Maxwell equations for a stationary ether and applying Lagrangian mechanics (see below), Lorentz arrived at the correct and complete form of the force law that now bears his name.

Which summarizes that to really understand the nature of the force, you gotta get serious with math.

I know it's sad, but I was talking to a friend who is studying Physics about the B-S law and got an answer which also summarizes into the above conclusion :( I study Chemistry and I am learning that, even if you learn and understand how to explain a lot of observations, if you question those reasons, you end up in a "believing" terrain. For example, last year I cursed Quantum Chemistry, and I found that I somewhat understood it (all you can understand something which tells us that particles jump through wall and all), but for that understanding, I had to accept a series of postulates.

Sorry I somewhat turned away from the original question, but I hope that you somewhat find it useful.
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Luned: http://www.scientificamerican.com/article/happy-birthday-electron/?page=1
Thank you for this!
Post edited February 10, 2015 by javihyuga
Posted February 11, 2015
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javihyuga: Using Heaviside's version of the Maxwell equations for a stationary ether and applying Lagrangian mechanics (see below), Lorentz arrived at the correct and complete form of the force law that now bears his name.
Warning: I'm a bit drunk right now.

I somehow intuitively understand that the Lorentz Force and Maxwell's equations are related, see my OP where I say understanding the Lorentz force might lead to me understanding radio waves.
Posted February 11, 2015
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justanoldgamer: snip
It's been years and I'm not even checking to remember what specifically you are trying to understand... but electromagnetic effects and their geometry are very torque / rotation dependent. Do you understand Coriolis effects well? That would be a somewhat more intuitive, yet still related to relative rotation motion.

Also the traditional (19th century) comparison is with fluid dynamics, though I suspect in this case that might not be in any way simpler. Have you seen or tried to do that type of comparison?
Posted February 11, 2015
The deepest you can go into the 'whys' is starting off with gauge symmetries. I guess that doesn't really help.
The best reason I can intuitively give for the direction of the force a charged particle moving through a magnetic field experiences is accepting that a magnetic field cannot alter the kinetic energy of an electrically charged particle - thus acceleration must not have a component parallel or anti-parallel to the direction of movement. To change the kinetic energy, an object has to have a magnetic moment via which it couples to the field.
Post edited February 11, 2015 by jdsgn
Posted February 11, 2015
Let me try to simplify the situation.

Let's start with the term "metal". Metals have a unique construction on an atomic level which essentially "frees" many of the electrons, allowing them to travel from atom to atom. Now, you should know that electrons have a negative charge. This is important as we next talk about magnets. As you also should know, magnets have a positive and negative side. We know that positive attracts negative and repels positive, the opposite for negative.

Now, lets string this metal (say copper wire) and wrap it in a consistent loop. Now when to give it juice, the electrons flow around the loop in a circle. Remember, that electrons carry an electrical charge. So when the electrons flows around in that circle, it acts just as a magnet moving in a same sort of circle. Both of these create a Lorentz force in the direction the charge or magnet travels.

So, what happens is nearby metals (with all those free electrons) and/or magnets now have this force exerted on them. The electrons (or negative poles of a magnet) are repulsed as the electrons from the first charge or magnet approach. They get pushed away. And they get pushed away in the direction the original electrons are moving. So as the electrons go in a circle, another coil or magnet starts moving in the same direction. It all comes down to basic magnetism.

The simplest way to think about it, is that electricity (current/electrons) act as little tiny magnets (well at least the negative poles of such).
Posted February 11, 2015
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RWarehall: Let me try to simplify the situation.

Let's start with the term "metal". Metals have a unique construction on an atomic level which essentially "frees" many of the electrons, allowing them to travel from atom to atom. Now, you should know that electrons have a negative charge. This is important as we next talk about magnets. As you also should know, magnets have a positive and negative side. We know that positive attracts negative and repels positive, the opposite for negative.

Now, lets string this metal (say copper wire) and wrap it in a consistent loop. Now when to give it juice, the electrons flow around the loop in a circle. Remember, that electrons carry an electrical charge. So when the electrons flows around in that circle, it acts just as a magnet moving in a same sort of circle. Both of these create a Lorentz force in the direction the charge or magnet travels.

So, what happens is nearby metals (with all those free electrons) and/or magnets now have this force exerted on them. The electrons (or negative poles of a magnet) are repulsed as the electrons from the first charge or magnet approach. They get pushed away. And they get pushed away in the direction the original electrons are moving. So as the electrons go in a circle, another coil or magnet starts moving in the same direction. It all comes down to basic magnetism.

The simplest way to think about it, is that electricity (current/electrons) act as little tiny magnets (well at least the negative poles of such).
Sorry but this is wrong. Magnets do NOT have a positive or negative side, they have north pole and south pole. This has NOTHING to do with electric charge. Electric charge is neither attracted to nor repelled from magnetic poles.
And a constant current equals a static magnet (roughly speaking).
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General discussionPhysic topic: The Lorentz force(21 posts)solved(21 posts)solved
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