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Physics Question: Magnets
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Dec 12, 2011, 08:53 PM
 
Magnetism is at the heart of modern technology. Moving permanent magnets through coils of wire (or vice versa) is the primary, and most efficient method of converting mechanical energy into electricity, and electrical energy into mechanical energy. In this situation, the magnetic field forces electrons to flow, and moving electrons create their own field that attracts/repels the poles of a magnet to produce movement.

Here's the questions: Does the field of a "permanent" magnet deteriorate over time? When magnetic attraction makes something move, how is the Law of Conservation of Energy observed? Where does the energy to move those things come from and does it "run out" or "get used up"? And finally, how "permanent" are permanent magnets?

I can understand and explain the quantum effects that allow transistors to work, but I can't yet get a grip on the forces behind how magnets work... Please enlighten me.

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Dec 12, 2011, 09:22 PM
 
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Dec 12, 2011, 10:28 PM
 
Good one. I hadn't found anything like that forum. The discussion did, however, ignore the situation regarding magnetic pull making something move toward a permanent magnet. Does the paper clip move to the bar magnet using some of the energy used to magnetize the bar magnet? If not, where did that energy come from?

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Dec 13, 2011, 12:15 AM
 
You will get a kick out of this

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Dec 13, 2011, 01:24 AM
 
Originally Posted by ghporter View Post
Does the paper clip move to the bar magnet using some of the energy used to magnetize the bar magnet? If not, where did that energy come from?
No it doesn't use energy used to make the magnet. Energy is conserved because the same energy that was used to pull the paper clip to the magnet is required to separate them. Think of this as converting potential energy to kinetic energy. Think of this as the molecular force that it is. Lets consider chemical reaction forces. Imagine you have a room that you have filled with 1 part oxygen and 1 part hydrogen. You only need one little spark and the whole room goes boom (binding the atoms to create water); does that mean you created energy from nothing? Or from just one little spark? Of course not. The forces of the charged particles had potential energy and when a spark occurred it caused the opposite charges to attract in a way that caused a reaction; a release of energy; but the same amount of energy is required to separate the hydrogen and oxygen again. We don't say that the charge of oxygen or hydrogen is free energy.

edit: for the record magnetism is a force, and energy is force x distance or something right?
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Dec 13, 2011, 02:29 AM
 
Let's make this a link, because it's distracting and rude as a picture.

Oh, and here's the picture that went with the link.

No offense, but I think it's inappropriate to turn a technical discussion into something more suited for high school lunch room discussions. And I'd have edited the post whether it was my thread or not...
( Last edited by ghporter; Dec 13, 2011 at 08:02 AM. )
     
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Dec 13, 2011, 02:30 AM
 
     
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Dec 13, 2011, 08:05 AM
 
Originally Posted by el chupacabra View Post
No it doesn't use energy used to make the magnet. Energy is conserved because the same energy that was used to pull the paper clip to the magnet is required to separate them. Think of this as converting potential energy to kinetic energy. Think of this as the molecular force that it is. Lets consider chemical reaction forces. Imagine you have a room that you have filled with 1 part oxygen and 1 part hydrogen. You only need one little spark and the whole room goes boom (binding the atoms to create water); does that mean you created energy from nothing? Or from just one little spark? Of course not. The forces of the charged particles had potential energy and when a spark occurred it caused the opposite charges to attract in a way that caused a reaction; a release of energy; but the same amount of energy is required to separate the hydrogen and oxygen again. We don't say that the charge of oxygen or hydrogen is free energy.

edit: for the record magnetism is a force, and energy is force x distance or something right?
Thanks! Both for the reminder about energy versus force and for the simple illustration of "energy used" to attract the paper clip. Much clearer now.

With so many technical levels involved, it's sometimes easy to trip over one of them and get muddled.

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Dec 16, 2011, 12:43 AM
 
The plane takes off.
     
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Dec 16, 2011, 07:18 AM
 
Originally Posted by FireWire View Post
Let's make this a link, because it's distracting and rude as a picture.

Oh, and here's the picture that went with the link.

No offense, but I think it's inappropriate to turn a technical discussion into something more suited for high school lunch room discussions. And I'd have edited the post whether it was my thread or not...
WTF?

That was funny.
     
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Dec 16, 2011, 07:33 AM
 
Maybe funny-ish, but quite distracting. And since I left the link, all are welcome to check it out. (I think intentionally creepier-than-usual clowns are a distraction to begin with...)

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Dec 16, 2011, 07:46 AM
 
Originally Posted by ghporter View Post
Maybe funny-ish, but quite distracting. And since I left the link, all are welcome to check it out. (I think intentionally creepier-than-usual clowns are a distraction to begin with...)
But you left Brien's photo up?
     
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Dec 16, 2011, 07:51 AM
 
Creepy versus creepy with vulgar wording... I left that one because it didn't seem quite as distracting. I probably would have done something about that one too if I'd thought more about it, but the vulgarity is what really caught my eye.

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Dec 16, 2011, 07:58 AM
 
Fair enough.
     
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Dec 16, 2011, 11:41 AM
 
Is this one better?

     
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Dec 16, 2011, 11:48 AM
 
Originally Posted by Brien View Post
I love this meme.

Too bad it illustrates that NN is starting to become out of touch with the internet.
     
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Dec 16, 2011, 09:16 PM
 
Originally Posted by Dork. View Post
Is this one better?

Is that John Inman?
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Dec 17, 2011, 09:50 AM
 
Originally Posted by The Final Dakar View Post
I love this meme.

Too bad it illustrates that NN is starting to become out of touch with the internet.
I'm sorry that removing an "F-bomb" from what had been a technical discussion makes it seem like I'm "out of touch" with anything...

I concur with the superiority of the newly placed image.


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Dec 19, 2011, 02:03 PM
 
Originally Posted by iM@k View Post
Is that John Inman?
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