Language:
To browser these website, it's necessary to store cookies on your computer.
The cookies contain no personal information, they are required for program control.
the storage of cookies while browsing this website, on Login and Register.
 Storing Cookies (See : http://ec.europa.eu/ipg/basics/legal/cookies/index_en.htm ) help us to bring you our services at overunity.com . If you use this website and our services you declare yourself okay with using cookies .More Infos here: https://overunity.com/5553/privacy-policy/If you do not agree with storing cookies, please LEAVE this website now. From the 25th of May 2018, every existing user has to accept the GDPR agreement at first login. If a user is unwilling to accept the GDPR, he should email us and request to erase his account. Many thanks for your understanding

Custom Search

### Author Topic: Magnetic force and distance  (Read 23919 times)

#### Shinecat

• Guest
##### Magnetic force and distance
« 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.

#### gyulasun

• Hero Member
• Posts: 4137
##### Re: Magnetic force and distance
« Reply #1 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

#### Shinecat

• Guest
##### Re: Magnetic force and distance
« Reply #2 on: January 20, 2006, 11:32:12 PM »
Thank you Gyula! Good pages.

#### ken_nyus

• Full Member
• Posts: 229
##### Re: Magnetic force and distance
« Reply #3 on: August 23, 2007, 08:38:31 PM »
This will help me too, thanks to the poster!

#### Honk

• Sr. Member
• Posts: 497
##### Re: Magnetic force and distance
« Reply #4 on: August 23, 2007, 11:14:49 PM »
This link will show how the force of a magnet will weaken by distance.

And here's a calculation on a 2x2x1" N50 magnet I made.

#### tropes

• Full Member
• Posts: 226
##### Re: Magnetic force and distance
« Reply #5 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

#### gyulasun

• Hero Member
• Posts: 4137
##### Re: Magnetic force and distance
« Reply #6 on: September 05, 2007, 04:06:12 PM »
Hi Peter,

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

#### tropes

• Full Member
• Posts: 226
##### Re: Magnetic force and distance
« Reply #7 on: September 05, 2007, 04:22:25 PM »
Hi Peter,
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

#### ken_nyus

• Full Member
• Posts: 229
##### Re: Magnetic force and distance
« Reply #8 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.

#### gyulasun

• Hero Member
• Posts: 4137
##### Re: Magnetic force and distance
« Reply #9 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

#### tropes

• Full Member
• Posts: 226
##### Re: Magnetic force and distance
« Reply #10 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

#### tropes

• Full Member
• Posts: 226
##### Re: Magnetic force and distance
« Reply #11 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

#### Honk

• Sr. Member
• Posts: 497
##### Re: Magnetic force and distance
« Reply #12 on: September 05, 2007, 07:27:45 PM »

#### Honk

• Sr. Member
• Posts: 497
##### Re: Magnetic force and distance
« Reply #13 on: September 05, 2007, 07:28:40 PM »
Here is a calculation on your magnet setup.

#### ken_nyus

• Full Member
• Posts: 229
##### Re: Magnetic force and distance
« Reply #14 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?