The amount of enery to move a magnet

[RichardBladh]

Hi all!

Maybe this is a dumb question but I have to know for sure.

If I have a series of magnets that is aligned one after another in one straight line, with each polarity reversed so that they repell eachother.
The magnets can only be pushed along the line. Moving one of the magnets in one direction would in effect mean that you would be pushing other magnets (in the same direction) as well.

So my question; is the required amount of enery / power that I would need to apply, to be able to move a magnet, relative to the number of magnets that I need to push to be able to move that one magnet?
My common sense tells me it should but I'm not certain. And if it is indeed so, is there a way to align polarity in such a way that you would be able to minimize the amount of enery. Based on i.e. "helping" magnets on the side of the line for instance...


ASCII art for your convenience:
-------------------------------------------------------
-M+ +M- -M+ +M- -M+ +M- -M+ +M- -M+
-------------------------------------------------------
^
|
| I want to push this in this direction ---->

Thank you!

Kind regards
Richard

 

[IRstuff]

conservation of energy says no. You could reduce the friction, but that's it

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[EdStainless]

The energy is a function of how much you compress the gap between the first two magnets.
That is your only work input.
Depending on how long the chain is I would guess that friction will be the largest part of the resistance.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[IRstuff]

Energy is force times distance. Force is the frictional resistance to be overcome. There is no free lunch here

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[RichardBladh]

Thank you all for your quick responses!

As I guessed, no free lunches here. I completely understand the concept of conservation of energy but I somehow imagined that you could harness some "stored energy" in the magnets. When I say stored energy I mean the fact that some forces are at work (repellation / attraction), seemingly without adding any forces when working with magnets. But I have to conclude that I don't understand (electro-)magnetic forces that well :-/

Again thank you and have a nice day!

Kind regards
Richard

 

[IRstuff]

Magnets have no "stored" energy; their fields are not that different from the electrostatic fields of charges. I think you've been reading specious materials.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[Compositepro]

Energy is force times distance. In this case the force is magnetic, not frictional. As you add more magnets and gaps the force stays the same but you have more gaps (distance). There is energy stored by the act of pushing magnets together. A close analogy is compressing a spring.

 

[RichardBladh]

Hi all!

@IRstuff - you are probably right - or the fact that I haven't read _enough_ about magnets...
@Compositepro - that was the analogy I was looking for and what I suspected was the case.

Damn, it would be nice with a "free lunch" wouldn't it ;-)
Interesting field nonetheless and I appreciate all the answers from you guys! I can now close the book on this subject.

Thanks!

Kind regards
Richard

 

[IRstuff]

The work in compression is released on expansion; but there's still no free lunch; the energy ultimately released is less than or equal to the energy the user exerted on the magnets. Otherwise, we'd all have free energy by now. The fact that no one has demonstrated under controlled conditions repeatable energy harvesting says it all. The only people claiming to have succeeded are all trying to sell you something that doesn't really work.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529