oh chronos my chronos

Factual Questions
1

so chronos, you have been providing a ownderful public sservice. i just wanted to say that upfront. we should bronze your brain and hold it as the acme for all to strive towards. anyway, enough (honest) fellating. here we go.

if i were a magnet, and my pole was placed near the opposite pole of another magnet, i would move toward it. now first off, would i feel a pull at my head, a push at my feet, a general attraction throughout? you don’t have to answer that directly, but it stems from the next question- how is the force being transmitted? is it some kind of magnetic gradient, or can the electromagnetic field be visualized as a rubber sheet (almost nonsensical stabs)?

get as hardcore as you feel, and as time permits.

awaiting to be sated, with bated breath,

jb

2

Well, for starters, the force acts on the entire magnet, but it acts most strongly on the portion closest to the other magnet. The short answer to how the force is transmitted is through a magnetic field. It’s a little more complicated than the electric field, which is the gradient of the electric potential; there is such a thing as a magnetic potential, but it’s a vector, not a scalar, and the field is the curl of the potential, not the gradient. If you’re not familiar with curls and dels and all that mathematical stuff, then disregard that; it’s similar to the electric field but more complicated.
As to why it works: A bar magnet has a bunch of electrons spinning in circles in it, like a bunch of current loops. Each loop acts like a bar magnet, itself, so to simplify the problem, let’s say that each of our magnets is a single loop of wire, with a current moving through each. A segment of the two wires might be represented like this:


+ + + + + + + + + + +
 - - - - - - - - - - -
+ + + + + + + + + + +
 - - - - - - - - - - -

where the + signs represent positively charged nuclei, and the - signs represent negatively charged electrons, moving to the right in both wires. However, these electrons are moving, so let’s take a look at the wires from the frame of reference of the electrons. In this reference frame, the positive nuclei seem to be moving to the left, and because of relativistic effects, the distance between them appears to be shorter:


++++++++++++++++++++++
 - - - - - - - - - - -
++++++++++++++++++++++
 - - - - - - - - - - -

The spacing of the electrons is normal, because they’re all moving with the same velocity, so in that reference frame, they’re all stopped, and there’s no relativistic effects. In other words, to an electron in one of the wires, it looks like the other wire has more positive charges than negative ones, so each electron is attracted to the other wire. On the other hand, if we look at it from the point of view of the positive charges, it’s the electrons that are moving, and therefore scrunched together:


+ + + + + + + + + + +
---------------------
+ + + + + + + + + + +
---------------------

so to a positive charge, it looks like the other wire is negative, so the positive charges are attracted to the other wire, too.
If these wire segments are part of a couple of loops, it’s slightly more complicated: The total number of protons and electrons must still be the same, and on the other side of the loop, the electrons are moving the other way, so the effect is reversed: It looks to an individual electron in one loop like the other loop is positive on the near side, and negative on the far side. However, since the electric force falls off with distance, the force from the near side of the other loop is stronger, so the net force is attractive.

Note also that the diagrams are greatly exaggerated here, and the relativistic effects are actually very small: Electrons in a wire typically only move at a few centimeters a second, which is MUCH less than the speed of light. Usually, we can completely ignore relativistic effects at these speeds, but they’re there, and when you take septillions of electrons, it starts to really add up.

3

chronos, I believe that is not quite what he was asking. You might want to read the tail end of the previous thread where I asked him to clarify.

4

Well I still don’t quite understand the question. If you are asking where the energy came from, the only possible answer is “potential energy” or “magnetism.” If an apple fell and hit you, where did that energy came from? It came from the fact that the apple was suspended high up to begin with, so it had potential energy. When the apple stem broke, the potential energy was converted into kinetic energy, and then into deforming your skull.

5

i’m not asking where the energy came from; i’m asking by what means the energy was transmitted. now, if i understand chronos’ reply, it was that to the negative charges, the positive charge of the other material seem preeety strong. and vice versa. so because of the motion of charges, each charge “senses” that its opposite is a lot stronger, and moves to equalize the charges.

my question is thus- by what means is a force transmitted? is it the sum force of the electrons trying to move to obliterate (or perhaps equalize) the charge? does each (or most) electron try and move toward the positive charge, thereby pulling its respective atom with it?

to make my question clearer, please take this example. gluons are particles which are responsible for transmitting a certain force. i am very unclear on how mostforces are transmitted. i understand the basics (such as an apple falling from a tree- the apple is constantly being pulled toward the ground, but the stem can equalize that force. once the stem breaks, the apple is impelled toward the ground) but not the esoterics (perhaps only esoteric to me). instead of the general physics behind the study of magnetism, i would like to know the specifics of what EXACTLY is moving the magnets. i think chronos may have answered the question for me (assuming my above understanding is correct), but my knowledge is shaky enough that i don’t know if i am right in my assumptions.

6

Let me have a crack at what I think the OP asked (thousand pardons if I answer the wrong thing). Magnetism is simply a field produced by imbalances of electrical charge. It costs energy to maintain a system of two distinct states, so any closed system (no energy going in or out) will try to find a balance where there is only one low energy state. In magnetism, this means that the positive and negative ends try to cancel each other out. Electricity is based on this fact, as the movement of electrons is based on a turbine engine maintaining an imbalance of charge. Anyway, magnetism can well be visualized in terms of a rubber sheet (it slopes up or down depending on which charge you are) but it is more accurately described as concentric circles. These circles run from the negative end to the positive end, and out both ends. It’s depicted in a rather informative way here, a page that also gives a nice picture of Earth’s magnetic field. So if you were a magnet, and you were on a magnet, you’d feel the attractive force about the same as you feel gravity now. BTW, if you want esoteric, get into the Standard Model (currently the grand theory of particle physics) and all the unresolved problems it has, as well as some of the proposed solutions. An introductory site to this whole thing is at http://www2.slac.stanford.edu/vvc/theory/model.html which is one of Stanford’s pages. Have fun.

7

This’ll teach me to miss the boards for a day… yes, gluons vector a force, but that’s the strong nuclear force, and we’re not interested in that here. The particle which vectors the electromagnetic force is the good ol’ photon, the same as the particle of light. My favorite analogy for this is a ping-pong game: Two players are interacting by exchanging a particle. If you suddenly shove one player out of the way, the system emits a particle. Similarly, two particles can exert forces on each other by exchanging other particles. OK, so it’s not a perfect analogy, but then, what analogy is perfect?

As to the forces on the electrons and atoms, you’ve pretty much got it… The charged particles, which feel the forces, pretty much pull everything else along with them.

8

Chronos - congrats on surpassing 1000 posts!