Yes but if it was a pole holding up the weight, removing the pole would allow weight to fall, so resisting gravity is not work? Helicopters work very hard to hover in the air?
So weight on a pole is potential energy, waiting to fall, like water in a dam... I guess I'm trying to explain it takes effort to resist gravity, the magnet does that, like a dam, but not like a helicopter hovering.
Grant.
Your fallacy is in thinking it takes power to generate force, even though Newton's law clearly states P = F*v. This fallacy arises by experience, because muscles require power to generate a force. Columns and beams and rocks clearly don't have to produce power to bear a load, proving Newton's observations.
The reason aircraft must use power to generate force is because they produce force against an unconfined fluid medium, something that can only be done statically in one way.* The medium squishes out from under it, so it has to constantly tread fluid to stay up.
*If the density is variable, you can float a blimp. Gravity produces a density gradient, pulling more air to the 'bottom', so you just need something lighter than air to take advantage of that difference. Fortunately, we need lift to counter gravity, so blimps and planes go with gravity quite naturally. If we didn't have gravity (but had atmosphere somehow), blimps would not be possible, and planes would be unnecessary.Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
They have this circular pipe that they painted the word "dream" on. Put a bunch of magnets all around it, in *just* the right places, and a ball bearing will travel round and round inside it forever. The sound made by the ball bearing generates an electric current in a transducer near the plane of the pipe "dream". The assembly works great, when there are no pertinent facts nearby.
Ed
I dunno, I think it would be cool to have a flywheel desktop toy which would turn for a few hours as it slowly demagnetized a permanent magnet. It might even be the key to a megabuck industry, like Dipping Bird or Chaotic Pendulum. Don't forget that entire vast alt-science community would all want to have one of their own. Set the price initially high!
Then build a non-gasoline car which lets you drive to work while it slowly ruins a few thousand pounds of rare earth magnets.
The field energy in your average permanent magnet isn't that high--it's more like a spring than a battery, even, let alone a tank of gas.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
The MRI machine at the local VA hospital is in a real tunnel. I got a migraine from the noise it made when they were looking for the cause of the sudden blindness in my right eye.
There's no work done, because even though there's force, there's no motion.
And I was surprised that there was a thing called a "keeper" that you could stick to your horseshoe magnet - as if shorting the "magnetic circuit" actually helped maintain the field!
Thanks, Rich
It does. Crappy magnets gradually decay with time, due to the motion of magnetic domain walls. The keeper reduces the magnetic field gradient at the surface of the magnet, resulting in less driving force for the domain wall motion.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Or from another point of view, it keeps the magnet biased with self-magnetization. Old magnets, like alnico, had a soft B-H curve, not nearly as square as later SmCo or NdFeB magnets. Alnico has a fairly impressive Bmax of 1.2T (typical of steel alloys and comparable to NdFeB's
1.5T), but it drops off to about 0.8T at 0 A/m. This is also why alnico magnets "burn in" with use (if anyone is old enough to have used new magnets..), and are easy to demagnetize when overdriven.Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
I wouldn't characterize AlNiCo magnets as crappy, and they demagnetize immediately without a keeper. They're great magnets, they've just got a limited amount of magnetomotive force available to maintain their flux density -- take away their keeper (or run too much current in the motor that they're the field magnets for) and they'll demagnetize.
Rare earth magnets are scary-strong, and have magnetomotive force that won't stop -- but the last time I checked an AlNiCo magnet would still beat any rare earth magnet, hands down, if the application temperature was high enough.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
I don't doubt that Alnico has its uses still, but for my money a magnet that dies when you look at it funny is a crappy magnet.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Fred, please remember to use the proper dot product notation. In early grade school, kids often learn the scalar product thing that is just plain non-physical; not even Newton used it. It leads to endless errors that are hard to un-teach.
For some unusual fun play with the physics of the gas torus and "smoke ring" of "Integral Trees" by Larry Niven.
Thanks, that made the connection for some of the odd structures i have seen with early magnetrons and such.
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