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View Full Version : Magnetic Relations at the point of connect and disconnect between two objects



BrentArsement
2012-Mar-13, 09:40 PM
I have been thinking and thought someone on this board could simply explain the answer.

As I hold two magnets, one in each hand, and bring them near to one another, they eventually have a direct magnetic connection. I determine this moment of connection by feeling them interact. I can also determine when they disconnect. Given a more advanced magnetometer, I can precisely measure the distance and force of the connect and disconnect relationship. Lets assume I have one of these magnetometers providing a precise distance measurement of the connect/disconnect moment; the level of force; and the reaction of the molecular structures occupying the space between. My questions are as follows:

- Will the two magnets disconnect at the exact same distance as where they connected, as I pull them apart?
- Is there greater magnetic force on the objects at the moment of connection or at the moment of disconnection?
- Are the elements (space) between the two magnets before the magnetic connection different in any way after they are disconnected?
- Why?


All replies will fascinate me, especially those from the experts. Thanks in advance.


Brent

billslugg
2012-Mar-13, 11:14 PM
There is no point at which the two magnets begin feeling each other's field. They always feel each other's field. The degree to which they pull or push against each other decreases by the inverse square of their distance. Even if they were at opposite ends of the visible universe, they would still feel some finite force.

The magnitude of the field in between the two magnets is also a function of the magnetic permeability of the material. The magnetic permeability is a measure of how strong a field is developed in a material upon the application of an external field. If you measured the field strength in between your two magnets when in a vacuum and then again when in air, you would find the field in air to be stronger by an additional millionth. If steel was occupying the intervening space then the field would be about a hundred times stronger. Various exotic alloys can boost this number to a million times stronger.

Gsquare
2012-Mar-14, 04:10 AM
Lets assume I have one of these magnetometers providing a precise distance measurement of the connect/disconnect moment; the level of force; and the reaction of the molecular structures occupying the space between. Brent

Magnetometers only give the magnetic FIELD strength (or flux density) and the direction of the field at any particular point in time and space.

However, if you measure the Magnetic field you can use a formula to estimate the force between bar magnets...provided you have the correct dimensions of the magnets and the separation between them....(and provided they are aligned head to head).
As BILLSLUG said, the force is approx. proportional to the inverse square of the distance between them.

See here under sub-heading "Force between Two Bar Magnets" for the formula and description....:http://en.wikipedia.org/wiki/Force_between_magnets

However, for very close distances this formula becomes inaccurate, and numerical simulations are needed.
In all cases (besides the usual parameters) the dimensions of the magnets make all the diffference in the forces between them as pointed out in the article...
...In particular...
For SMALL magnets where the Length of the magnets become very small (dimensions can be neglected) the equations for the field, B, and the force, F, begin to get closer to what is called a dipole-dipole interaction,

In this case the Magnetic field now varies as the INVERSE CUBE OF THE DISTANCE, R; and the force between them falls off as the inverse FOURTH POWER of the distance..
See later formulas in the same post. http://en.wikipedia.org/wiki/Force_between_magnets under last heading Magnetic Dipole Interaction.

G^2

NEOWatcher
2012-Mar-14, 02:40 PM
Another good visualization is the old steel filings on a paper with the magnet underneath.

You will see how closer to the magnet, the field overcomes the friction of the filings on the paper more toward the magnet.
The filings become less organized as the friction becomes stronger than the pull of the magnet.

BrentArsement
2012-Mar-15, 10:38 PM
Thanks for the replies. GSquare, what of these numerical simulations? Am I understanding that with some objects near to one another, simulations replace knowns?

Perhaps I should have included the field. As I understand the field, it is 'constant', therefore used in formulations of the forces of two objects. However, the field can change as a constant, based off other objects (not the two objects drawing near/far) interacting within the field. So, as other objects affect the fields strength, local to my two objects, does the force of the two have to be calculated under new/changing constants? If so, does this pertain to the numerical simulations GSquare mentioned?

Thanks for the input.



Brent

HenrikOlsen
2012-Mar-15, 10:54 PM
Thanks for the replies. GSquare, what of these numerical simulations? Am I understanding that with some objects near to one another, simulations replace knowns?
Simulations replace simple, easy-to-calculate approximations because they stop being good approximations at that range.

cjameshuff
2012-Mar-16, 03:48 AM
Simulations replace simple, easy-to-calculate approximations because they stop being good approximations at that range.

And numerical simulations are used instead of exact solutions because exact solutions are often impractically complex or outright impossible.

Gsquare
2012-Mar-16, 05:24 AM
Perhaps I should have included the field. As I understand the field, it is 'constant',


That is incorrect, Brent.. I didn't realize you didn't understand the basics of a magnetic field around a magnet.

For any particular magnet he strength of the field is constant in time, but it varies with DISTANCE from the magnet. It is only constant at any particular distance from the magnet. The equations are written to show how it varies WITH DISTANCE.

See this graphic of the field lines around two magnets. http://en.wikipedia.org/wiki/File:VFPt_cylindrical_magnets_attracting.svg
For two magnets at a constant distance apart you can see that the field lines are closer together near the poles ....which means the field strength is greater near the poles. At the place where the lines are farther apart the magnetic field is weaker.

Exactly what is it you are trying to find out?
Maybe you should ask precisely; like "What is the force between two magnets separated by 2mm.?", or whatever.

G^2

BrentArsement
2012-Mar-16, 06:30 PM
Sorry G^2. I used the word 'constant'. I know the field changes, though to formulate the magnetic force of two objects, we need the field that the two objects are interacting within to be constant for calculation purposes. It becomes too difficult to calculate two objects if the field is fluctuating in the greater magnetic spectrum.

So i'll reword the idea of the field as follows:

When two objects draw near/far from one another, and we are calculating the force between them; and there are other objects within the field that affect the overall field as it relates to the two objects, how is it possible to accurately measure the relation between the two objects in my hands, if the field is in a constant state of change because of other objects interacting, assuming that the larger field isn't 'constant'?

My ultimate question, given some of the basic discussions from you and others is: Can we truly quantify magnetic force between two objects if the greater field is changing around them?

Remove my simple magnetic experiment from my hands and place it within Milky Way's galactic magnetic field, including our own heliosphere and the planets within. Can we confidently say that we can measure the forces of these objects, as they interact with each other within the larger galactic field, considering the fact that the field changes as multitudes of objects interact throughout the field? I see the field in such constant change, that it would be nearly impossible to have knowns in the larger galactic field.

The idea fascinates me and thanks for continuing this discussion.



Brent