Magnet question

True. Such motors have been built and do work. And they are very inefficient. .

If there's a complete circuit around a loop that contains flux, and the flux changes, you'd expect a current to flow. If there's resistance in the circuit, then that will cause an energy loss.

It would depend on the orientation of the loop whether there's any flux through it, and thus whether there's any change in flux.

Sylvia.

Thanks for the link.

It occurred to me after posting that maybe the presence of the screw increases the effective curie point. If I understand the mechanism of the curie point, it's the point where the domains have sufficient energy to move away from their aligned positions, thus destroying the magnetic field. However, if the field is more intense, because of the presence of the screw, then the domains would presumably require more energy. That is, the the effective currie point temperature has increased.

At the point where the screw falls away because the field has disappeared, the magnet would then be above the temperature it would need to reach to destroy the field in the absence of the screw. It now need to cool down somewhat before it can pick up the screw again. The extra energy is irretrievably lost, thus defeating any attempt to make a free energy machine this way.

This wouldn't manifest as a change in specific heat except about the curie point temperature.

Sylvia.

Harry, this statement is either total ignorance of electromagnetics or a complete lie. You tell us which one it is! The truth is that were it not for non-conservative fields electrical engineering would be quite simple and boring (no, batteries, no transformers, etc. Just balloons rubbed on cats...)

I just don't understand how it is that the person publicly displaying the most blatant ignorance of subjects are the very ones who are always suggesting that someone "take a course". Harry, it is YOU who is in need of a course in electromagnetics. I'll even give you a FREE lesson.

The following from the classic FRESHMAN physics text Halliday and Resnick Page 757.

"Electric fields associated with stationary charges are conservative, but those associated with changing magnetic fields are nonconservative. See Section 8-1. Since electric potential can only be defined for a conservative force, it is clear that it has no meaning for electric fields produced by induction..."

Note that shoving iron (screws or other ferromagnetic materials) in the flux path of magnets produces changes in the field's distribution in space hence, "changing fields".

I hope you are pleased with yourself that you just demonstrated to the world in a public forum that you do not understand this subject even to the Freshman level. I urge you to consider a college education starting with a freshman course in basic physics. And I'm talking about a REAL physics course not the mathless "physics appreciation" courses that "science" teachers take today.

Benj

Just to be perfectly clear, we cannot shield one end of a magnet. The covered pole just gives a magnet with one end bigger than the other. In other words, more screws will be attracted to the growing blob of screws until it's large enough to enclose the other pole and all the flux in between.

-- Joe

However, the addition of each screw changes the shape of the field. It will not be always possible to add a new screw at an arbitrary place on the outside of the growing blob, even when there remain places where it is possible to add a screw.

Sylvia.

Interesting COE issue:

As the first screw is yanked up to the magnet, a certain amount of work is done. That work could be recovered by having the screw drive a tiny winch and generator on its way up. If that's not done, the screw will slam into the magnet and waste that energy as noise and heat and deformation and EM radiation and magnetization of the screw itself.

Any eddy currents will also heat the screw on its way up, again wasting the energy.

Since the magnet was magnetized using some finite amount of energy, no more than that amount is available to lift screws. So the number of screws that can be lifted is limited by some sneaky geometrical considerations. COE is often sneaky.

Nothing inherently limits the number of screws that will stick to the magnet, provided the magnet doesn't have to do work to add more screws.

John

Still, if a screw will stick to the magnet, or the growing blob of screws at some point, then there must be at least some force holding it there, and some work would be done on the screw as it approaches.

But I agree about COE being sneaky. It's often far from obvious how the Universe keeps track so as to balance its books.

Sylvia.

I wonder if the earth loses gravitational field when meteors fall into it?

:)

When the screw 'falls into' the magnet, it is giving up potential energy... you get energy when you move a screw from infinity to the magnet. The screw will exchange its potential energy for kinetic energy, first in the form of motion, and then in the form of heat in the magnet.

Note that the screw won't move unless the net energy of the system is less than before, meaning that the potential energy loss the screw wrt the magenet is greater than the potential energy gain of the screw wrt the earth's magnetic field. So, some energy is given off in this exchange, in the form of heat.

Regards, Bob Monsen