Stephen A. Lawrence wrote: > > > Paul wrote: >> Stephen A. Lawrence wrote: >> [snip] >> >> You mean sci.physics.relativity.pub? I'd like to >> know >> >> where physicists such as Ed Witten hang out >> online. :-) >> > >> > The news group "sci.physics.relativity". It's >> crawling with total >> > loonytunes with just a few real physicists. Ed >> Witton doesn't sound >> > familiar; I don't think he hangs out there >> (probably has more sense). >> >> Well you should recognize the name Ed Witten. He's >> the guy who took all the nightmarish flavors of the superstring >> theories and created >> M-theory! :-) He's almost worshipped in the physics community. >> >> >> >> [snip] >> >> Yes, understandably, but I'm just trying to come >> up >> >> with ideas to meet the demands of conservation of >> energy. I'm sure >> >> there must be some >> >> genius QM physicists out there that have an >> answer. So far haven't >> >> met any with an >> >> answer, but I would expect some silly answer such >> as, "Oh yeah, the >> >> energy comes at the cost >> >> of information. The probability of knowing the >> electrons location >> >> decreases." ;-) >> > >> > Actually as I think about this it seems like the >> overall field strength >> > and, hence, field energy must decrease as two >> dipoles approach (due to >> > the fields of the two dipoles "mostly canceling"). I don't know if the >> > reduction in field energy matches the gain in >> mechanical energy but it >> > might. >> >> No, no, no. Two magnetically aligned dipoles increase >> the net magnetic field. > > That's true, but two aligned dipoles don't attract each other.
No, it's the process of two *unaligned* dipoles in the act of rotating to alignment. That generates kinetic energy in addition to an increase in net magnetic field. > You need to flip one so they're N-S, S-N for there to be attraction They attract until they are perfectly aligned NS NS. >, and in that case the fields cancel as they approach. That's not true. When aligned they are NS NS. That is full magnetic alignment and they do *not* cancel. The net field increases. > If they're identical > (but with one flipped), and if you could move them together until they > were co-located, you'd have zero net field. > > Here's a picture of two dipoles, oriented vertically, which will attract > each other (using coils produces the same result but is harder to draw > in flat Ascii than the "mythical" two-charge dipoles): > > > N S > | | > | | > | | > S N Again that is half magnet alignment. Also your drawings look more like rods, not dipoles. ;-) Here's fully unaligned (max cancellation) --> NS....SN Here's half alignment --> N....S S....N Here's full alignment (max net field) --> NS....NS > When they are allowed to go all the way together, so that they're > touching, the colocated N and S "charges" produce canceling fields: > > NS > || > || > || > || > SN A lot of people get this mixed up, but it becomes clear when one understands that the magnetic field in front of a dipole is twice the density as the sides. That is why full alignment is NS NS, when the poles are *facing*. That's why your above diagram is half alignment. [snip] >> > That, on the other hand, leads to problems in the >> case with two >> > electromagnets, where the same reduction in total >> field strength must >> > occur, _but_ where we've already paid the energy >> bill by overcoming the >> > back EMF in the coil as it moves through the >> field.... >> >> >> Again, you have it backwards. See above comment. > > I think I have this straight, but I may have said it wrong. > > If we place two relatively INVERTED electromagnets next to each other, > they attract each other, and if we allow them to come together, there's > a back EMF as they approach, and we need to add electrical energy to > maintain the current in the loops. If we have two ALIGNED > electromagnets, to bring them together, we need to _force_ them together > (they repel) Two aligned electromagnets do not repel. They *attract*. > and as we do so, there's an induced forward EMF -- we get > electrical energy out. That's backwards. :) As they attract and move closer there's back EMF, which consumes energy from the battery. Regards, Paul Lowrance ____________________________________________________________________________________ Finding fabulous fares is fun. Let Yahoo! FareChase search your favorite travel sites to find flight and hotel bargains. http://farechase.yahoo.com/promo-generic-14795097
