Magnetic Metal Repulsion Possible?

Have you had a look at the following links, they explain the overall subject in great detail.

http://en.wikipedia.org/wiki/Magnet

http://en.wikipedia.org/wiki/Magnetism

http://en.wikipedia.org/wiki/Magnetic_field

A good place to start. There is also enormous amounts of information available on the subject on the internet.

Hi MJ,

Magnets only attract some metals, called Ferrous Metals. Here's more info (I took the following from this website)

Magnets attract to ferrous metals such as iron, nickel, cobalt, certain steels and other alloys. Brass, aluminum, copper, and most stainless steels, however, are non ferrous.

The reason magnets attract ferrous metals is because these metals are almost magnets themselves. If you look inside them you see the following:

In an unmagnetized ferromagnetic material, domains point in random directions.

Bringing a magnet close to a ferrous metal aligns the magnetic domains in the metal (see diagram below). When the domains are aligned, there is a net magnetic field. You end up with two magnets, polarized in opposite directions, the original magnet and the magnetized ferrous metal. Since the metals are polarized in the opposite direction, they are attracted to each other.

In a magnet, most or all of the domains point in the same direction.

If you wanted a magnet to repulse a piece of metal, you'd need two magnets. The first you would use to align the magnetic domains of the ferrous metal. Remember, this will give the metal a polarization opposite of the magnet, which means the metal would be attracted to the magnet. Now if you apply a magnet of oppisite polarization to the metal, it will be repulsed (or experience a torque as it tries to align itself with the ferrous metal).

I rushed through this explanation and may have made some mistakes, anyone catching some mistakes feel free to correct me, I'd appreciate it. I think I'm in the ballpark here though.

Roger

Good explanation. two magnets... I need to make some experiments but It has been of great help.

What I want to do is to repel a diamagnetic metal with a superconductive magnet. I just need to build a superconductive magnet and make some tests. :)

I will also search about superconductive magnets and diamagnetic materials.

Hi Jedi,

Working with diamagnetic materials requires cryogenics, especially with metals, which have a superconducting temperature often between 2 and 30 Kelvin - i.e. you need liquid helium to cool it to that temperature. A better option is to use the new wave of 'high' temperature ceramic superconductors like YBaCuO and BSSCO, (which are commonly available) you can achieve superconductivity with liquid nitrogen cooling, up to about 135 K. There are two (apparently different, but ultimately unified) theories as to how superconductivity works. Basically, the molecular structure of the material below its superconducting temperature is such that an incident magnetic field causes the electrons to spin in a pattern which produces a reciprocal magnetic field, thus excluding the field from the material and producing a net repulsive force. In otherwords, moving any magnet in the vicinity of the superconductor will result in a repulsive force.

hope that helps

As far as I know, the only way for a Magnet to repulse metals is to magnetize the metals, and oppose the poles.

I believe the simple answer is best said with a quote: "Thats a Negative Raptor-man"

But: I have been dead wrong on numerous occasions, on numerous subjects.

HowStuffWorks "How Rail Guns Work"

sweet... The difference of a rail gun and a coil gun... beautiful....

Nice pictures but in the end of the article there is a mistake: the magnitude of Lorentz force in the case of a rail gun is proportional to the width of the projectile, not to the length of the rails. Longer rails give more momentum to the projectile because the duration of force application is longer and the mouth velocity is higher. However, temperature is a limiting factor in making long rails. The projectile can melt before reaching the gun mouth. Friction and rails' wear are real drawbacks of this design.

Friction.... soo.... how can you make it a non friction repulsion? Could this be possible? why is this not possible? Maybe you could use the superconductor also.. to levitate the proyectile....

by the way.... I haven't seen a coil gun in my life

By definition, the rail gun needs the friction contact to rails to close the circuit and generate propulsion.

If you think of a contactless design, forget about the rail gun.

I don't think coil guns have been made at full scale of a weapon.

Overall, you're on the right track (or rail? :) of thinking.

Only the electrical contact is needed. The friction is just icing on the cake.

TRUE - the only reason I said "friction contact" is because there is no such thing like a sliding electrical contact without friction. Brushes are doing this job in motors and generators at lowest reasonable friction. Even mercury contacts have friction.

Why is this happening? Apparently, electrons love friction for migrating from one body to another. Same is happening in the Van de Graaff electrostatic generators and the like.

Thanks for accuracy.

If you have a different opinion on this, I'm ready to learn.

So maybe the proyectile can have some kind of conductive non magnetic brush surrounding it? like an arrow with a tail.... I guess that would have lower friction, but at those speeds my guess is that it would melt like swiss cheese. And how would it hold to the projectile... there must be a way...

I hope you know making weapons in your backyard is illegal in most countries.

You're a good thinker and sooner or later you'll find a way to work around friction and other things. My suggestion is to keep them at concept level and then contact a registered military contractor in your country to build the real thing.

You know that saying: whatever scientists are working on, they always end up in making a weapon...

Wonderful consept...

This is the picture:

On the same same consept, will the following arrangement work as a Motor?

No,

The two ends of your armature are being forced in opposite directions.

You just need to complete the loops where they are broken at the back of the picture and add another + and -at the front (+ above the - , - above the + ).

Do you mean this arrangement?

No I didn't, I meant like this:-

but, now I think I understand it, your design is much better.

Check out these links concerning the Meissner Effect. The last one is a really cool YouTube vid. (pun intended):

ME1

ME2

ME3

I recall seeing a demonstration where an aluminum pendulum was prevented from traversing between two magnets by the lines of force from the magnet which the aluminum could not cut. IF you have the magnets you can try this, I'm on road till saturday and no magnets to set this up at the holiday in express.

Perhaps someone else has seen this effect?

milo

"Perhaps someone else has seen this effect?"

Yes. Aluminum's paramagnetic properties were exploited to good effect in 'tuning' the period of special, highly accurate pendulum clocks used in astronomical and other scientific work in the late 19th and early 20th Centuries. The most accurate of these was the Shortt-Synchronome pendulum clock. This clock was so accurate - better than 10 milliseconds per day - that it led to the discovery of variations in Earth's rotational rate.

In a different application, Motorola used moveable aluminum rods to tune early AM car radios. Unlike their ferrite-core-based cousins, the inductance of aluminum-core coils decreases as the core is inserted.

Welcome Back, Europium.

Thanks for the followup.

milo

On my desk I have the magnet assembly used to control the head position in a hard disk drive:-

together with an aluminium disk (which happened to come from the same drive: it held the disk itself in place on the spindle).

If you hold up the magnets, and, drop the disk through the gap, it falls in slow motion until it exits at the bottom.

It's a very compulsive "toy".

Effectively the whole thing is working simultaneously as a generator, and, a motor. The movement of the disk between the magnets creates eddy currents in the aluminium; the eddy current in the magnetic field generate a force, but, the whole thing can only oppose the movement i.e. slow things down.

You just need a few good torque screwdrivers to get most old hard disk drives apart.

Unfortunately: this does not quite fulfill Manufacturing Jedi's requirement.

Hi Milo,

I think I've seen this used as a dampener on a set of scales - can't remember just where or what brand. An Al plate was attached to the free arm and it passed between two stationary magnets. Every time the Al piece passed back and forth between the magnets, it slowed the arm down, greatly reducing the time needed to stop the oscillations.

Now I see Randall has posted something similar.

Hi Jedi. Imagine that a permanent magnet approaches a ferromagnetic rod as I show in the next figure:

As Roger already said, the ferromagnetic materials consist of many tiny areas which are magnetically polarised (sth like tiny magnets). All these tiny magnets are randomly dispersed at any direction (as long as there is no external, nearby magnetic field) and their tiny magnetic fields cancel each other. So, initially, the rod of this picture does not behave as a "magnet". But, when an external magnet approaches this rod all these tiny magnets of the rod are re-arranged under the influence of this external magnetic field. All these tiny magnets have, now, the same orientation and their tiny magnetic fields are "added" giving us (macroscopically) a total magnetic field. The result is that the rod behaves, now, as a "magnet".

Now, it's easy to understand why a magnet will -always- attract this ferromagnetic rod: In the picture, the S pole of all these tiny magnets "looks" to the left (as their are attracted by the N pole of the magnet which "looks" to the right). As a result, the S pole of the total magnetic field of the rod "looks", also, to the left. Hence, the N pole of the magnet and the S pole of the rod are facing each other and (because of this) the magnet and the rod are attracting each other.

I hope that I've helped you.

Some materials are weakly repelled by a magnetic field, for example, bismuth metal and pyrolytic graphite. Look up diamagnetism.

http://en.wikipedia.org/wiki/Diamagnetism

The answer to your first question is diamagnetic metals - they respond with an opposite magnetic field to any externally applied magnetic field. As a result, they are repelled by a magnet, regardless of its poles position. The most diamagnetic metal at room temperature is Bismuth. Mercury and Gold also have a weak diamagnetism.

Do not expect to get the same repulsion forces between a bar of bismuth and a permanent magnet as between two magnets facing same polarity. Diamagnetic forces are weaker by several orders of magnitude. However, they are measurable.

Ok, here goes: What would it take for a magnetic field to stop a bullet?

Finally, you're in the active armoring field...

I have a concept on this one. If you have a client, let me know and we can partner.

A LOT of magnetic force. They tried on a TV episode of 'Mythbusters'.

http://kwc.org/mythbusters/2008/01/episode_95_james_bond_special.html

Slight bullet deflection but rather impractical (like their pizza box shield).

Our local city recycling plant zings its aluminum bits out of a falling stream (after removing paper, ferrous metals, and so on) by magnetic replulsion/ attraction. Not with permanet magnets though... If you put the bits into a rapidly changing electromagnetic field, you get an induced current to flow in each, which is then used to force them where you want, rather like the armature of a motor.

Like all cool technology, it is magic at first, but quite logical once you undertand it.

Very interesting. Will check on that.. maybe we can recycle aluminum like that in our recycling facility.

This effect is called diamagnetism and there are certain materials exhibit this property,

Here you can find more details.

http://en.wikipedia.org/wiki/Diamagnetism

When it comes to repulsion using magnets I'd vote this machine as the winner:

http://en.wikipedia.org/wiki/Shanghai_Maglev_Train

Linear motor, induce a current with an opposing magnetic field, similar to sorting the aluminium from the recycling.