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Mechanical free energy devices => mechanic => Topic started by: Shinecat on January 20, 2006, 02:17:38 PM

Title: Magnetic force and distance
Post by: Shinecat on January 20, 2006, 02:17:38 PM
Hi all!

I am working on another permanent magnetic motor geometry.
In the past month i complete a geometry. At the moment i don?t know it is possible to work, or not.
But have a question:

What is the mathematical connection between the magnetic force strenght and distance?
What is the simple / simlified formula which symbolize this connection?

Other words?
Take two magnets and put them near together with the same poles. The magnets are repulsing themselves.

When the distance is increasing in linear way, the magnetic force strenght decreasing linear?
Or exponential? Or how?

So, what is the formula of decreasing?

I think it is an important question, if anyone want to create working and useful designs.
Thanks everyone, who answer me, and sorry for my wrong english.
Title: Re: Magnetic force and distance
Post by: gyulasun on January 20, 2006, 06:58:32 PM
Hi,

I quote from a page:

<<Elementary physics states that the magnetic field of a magnetic dipole is approximately proportional to the inverse cube of the distance from the dipole. Therefore, if you double the distance from the magnet, the magnetic field strength will be reduced (roughly) by a factor of 8. >>

I think there are further interesting details on your question here:

http://www.exo.net/~pauld/activities/magnetism/forcebetweenmagnets.html    and also here:

http://van.hep.uiuc.edu/van/qa/section/Electricity_and_Magnets/Magnets/20050220232939.htm

Good experimenting.

rgds

Gyula
Title: Re: Magnetic force and distance
Post by: Shinecat on January 20, 2006, 11:32:12 PM
Thank you Gyula! Good pages.  :)
Title: Re: Magnetic force and distance
Post by: ken_nyus on August 23, 2007, 08:38:31 PM
This will help me too, thanks to the poster!
Title: Re: Magnetic force and distance
Post by: Honk on August 23, 2007, 11:14:49 PM
This link will show how the force of a magnet will weaken by distance.
http://www.imstrading.com/cgi-bin/flux-graphs.pl
You must register for free to be able to use it.

And here's a calculation on a 2x2x1" N50 magnet I made.
Title: Re: Magnetic force and distance
Post by: tropes on September 05, 2007, 03:09:30 PM
Good links but none of these links answers the question," What is the attraction and repulsion force of 2 given size magnets at a given distance?"
For example: I have two Neo 40 disc magnets attracting each other 1 inch apart. The surface area of each magnet is 11/14 square inch. The magnets are 1" in diameter and 1/8" thick.
Peter
Title: Re: Magnetic force and distance
Post by: gyulasun on September 05, 2007, 04:06:12 PM
Hi Peter,

I found this link: http://www.magnetsales.com/Design/DesignG.htm

And this: http://www.magnetsales.com/Design/Tools1.htm and this: http://www.magnetsales.com/Design/Calc_filles/PullAndPushBetween2DiscMagnets.asp

I understand the calculations are approximations.  Use material N39H for N40 to approximate it ( no N40 material is included...)

Gyula
Title: Re: Magnetic force and distance
Post by: tropes on September 05, 2007, 04:22:25 PM
Hi Peter,
I found this link: http://www.magnetsales.com/Design/DesignG.htm
And this: http://www.magnetsales.com/Design/Tools1.htm and this: http://www.magnetsales.com/Design/Calc_filles/PullAndPushBetween2DiscMagnets.asp
I understand the calculations are approximations.  Use material N39H for N40 to approximate it ( no N40 material is included...)
Gyula
Thanks Gyula
Good calculator at magnetsales.com. The answer is given in " gauss at X" . How do I convert that to lbs.?
Peter
Title: Re: Magnetic force and distance
Post by: ken_nyus on September 05, 2007, 04:41:40 PM
Thanks Gyula
Good calculator at magnetsales.com. The answer is given in " gauss at X" . How do I convert that to lbs.?
Peter

It looks like the "push" and "pull" numbers below the "guass at X" are the forces in pounds.
Title: Re: Magnetic force and distance
Post by: gyulasun on September 05, 2007, 04:44:05 PM
The answer is given in " gauss at X" . How do I convert that to lbs.?

Hi Peter,

At this link I included in my previous post  http://www.magnetsales.com/Design/Calc_filles/PullAndPushBetween2DiscMagnets.asp you get not only Gauss at X but the attract and repel force in Pounds so you do not need to convert.  (By the way they have a conversion help here: http://www.magnetsales.com/Design/Tools1.htm#units )

Gyula
Title: Re: Magnetic force and distance
Post by: tropes on September 05, 2007, 06:04:35 PM
Thanks guys
I finally hit the correct link and plugged in some actual numbers. I have two Neo42 disc magnets each D= .75", length= .5" and Distance apart is 1.25". Now the calculator says the pull= 70.9!!
Now I say bullshit. I can hold these two magnets one on each side of my hand and there is not 70 lbs of pull. Great calculator but the results are questionable or I did something wrong.
Peter
Title: Re: Magnetic force and distance
Post by: tropes on September 05, 2007, 07:14:20 PM
Okay, I went back and tried again. Now I get 0 lbs. pull and 0 lbs of repulsion.
Peter
Title: Re: Magnetic force and distance
Post by: Honk on September 05, 2007, 07:27:45 PM
Try the IMS Trading calculator as suggested. A lot more advanced.
http://www.imstrading.com/cgi-bin/flux-graphs.pl
Title: Re: Magnetic force and distance
Post by: Honk on September 05, 2007, 07:28:40 PM
Here is a calculation on your magnet setup.
Title: Re: Magnetic force and distance
Post by: ken_nyus on September 05, 2007, 07:45:12 PM
Why does the flux density increase when the magnets get further apart?

Maybe flux density is not what I think it is? what does this graph say?

As the magnets get further apart, then the flux density increases?

What does this mean?
Title: Re: Magnetic force and distance
Post by: Honk on September 05, 2007, 08:47:42 PM
It does not increase. You have read the table backwards.
Title: Re: Magnetic force and distance
Post by: ken_nyus on September 07, 2007, 12:25:20 AM
Ah, I get it now, 0 is the center point between the two magnets, and 0.625 is at the face of one of the magnets.

Thanks.
Title: Re: Magnetic force and distance
Post by: ruin41 on October 16, 2007, 04:31:01 PM
Wow its good to see that there is information available these days ...there wasn't when i started on this stuff ... good to see the right questions being asked too.

If you want an easy way to figure out the "power" of a given magnet it is easy ... use your kitchen scales ...stick a magnet on them and push against it with another it reads pounds or kg ... simple enough to understand and accurate magnet strength comparison.

If you have the wall mounted plastic scales like i do then you can put a magnet in the bowl and test the pull power as well from underneath.
Title: Re: Magnetic force and distance
Post by: Craigy on December 01, 2007, 03:30:04 AM
It is good to use the magnet sales calculator  http://www.arnoldmagnetics.com/mtc/calc_gauss_cyl.htm
when using a cheap Hall based Gauss meter, The a1301 or a1302 will normally saturate at more than a 1000 gauss, so if move to a point say half an inch away from the magnet under test we can calculate its surface flux value. The formula used on that page is this, Below that i have transposed so that you can work out your surface flux by taking a reading on your cheap gauss meter some distance away from the surface.


Title: Re: Magnetic force and distance
Post by: Honk on December 02, 2007, 01:00:29 PM
This magnet calculator is better.
http://www.magnetsales.com/Design/Tools1.htm