[Corvettaholic]

As you all know I'm not that technical, so I'm going to explain this situation in non-technical terms. Lets say I have two NIB (neobydium or something, iron, boron) magnets, aka rare earth magnets. Both are 1"x1"x1" blocks. One has a 'pull strength' of 1 pound, the other has a pull strength of 10 pounds. I'm also not very metric friendly, by the way. Lets say I have a 10 pound chunk of steel. How do I figure out how far away I should place the steel from the magnet before it starts dragging it across the table? Assume the table is frictionless for simplicity.

There is a point to this, and some of you might be wondering what crazy experiment I'm trying to dream up this time...

It involves that thingy with Newton's balls and transferring kinetic energy.

[arnyk]

This sounds like a physics question to me.  The way I see it, when you say that it has a "pull strengh" of 10 pounds, would that be the max or the min?  Each magnet has its own magnetic field which is strongest at the poles, but the actual 'pull strength/force' will vary depending on the distance.  So the pull force really depends on distance, it is not constant at 10N or something all the time.  There's a formula to calculate the forces acting between two masses...umm...  F = ke1e2/d^2...  Actually I'm drawing a blank here -- haven't done this stuff since high school  .  Lemme brush up on this, or wait for a real physicist.

Edit: Correction, that would be the formula for the forces between two charged masses.  Bleh, so rusty.

Random facts that won't help:
-magnetic field strengh measured in Teslas (T)
-pull strength would probably be in newtons.
-The kinetic energy acquired by say a paper clip accelerating towards a magnet is equal to loss of magnetic energy in the field.

Having said all that, is it possible to just keep inching a certain object closer and closer to the magnet until it goes on its own?  Then that would be your optimization point.  Pretty simple...unless you're doing something alot crazier which needs to be perfect on the first try or else we're all screwed.  

[Borek]

Attraction force (or pulling force - no idea how it will be in English) changes as 1/r^2 (just like gravitational or culomb force). So if your table is frictionless distance doesnt matter - magnet and the steel chunk will pull each other and they will be moving towards the mass center. The only thing that changes with the distance is the time needed for both things to crash.

[Corvettaholic]

I just now remembered something very important! So lets say the pull strength is 10 pounds, or however many newtons like its supposed to be written, and that strength is at the pole itself. Sounds correct. So lets say you go 1 distance unit away, and the field strength goes down by a factor of half. Go to 2 distance units away, and the field goes down by half AGAIN. So its exponential.

arnyk: You're idea about slowing inching the object closer until it pulls itself is a good idea. That kind of scares me though, because the magnets I plan on using will smash my hand into a pancake, or if an object slams into it then it will shatter.

Oh! About magnetic fields... so lets say (again) you have some random magnet. Next you stick a chunk of steel on it. The steel is now part of the magnet. Does the field strength remain the same, get weaker, what? Does the field extend farther out? I'm going to buffer the magnet with a steel chunk because its more elastic (haha, steel being elastic) than the magnet itself. This should help prevent shattering.

Basically what I'm trying to is this:
http://www.scitoys.com/scitoys/scitoys/magnets/gauss.html

But on some serious steroids. New pansy little magnets for me! I'm talking HUGE ones, but then I have to figure out spacing. I'd also like to use a solid frame, steel comes to mind, but I dunno about a metal frame and magnets... If all goes well the goal is to launch a ball bearing, or whatever, through an old 70's chevy truck. Those things are solid iron! Heehee... Its also part of my competition I'm in. Bunch of us guys have to design something to launch a steel ball bearing as far as we can without using explosives.

FYI: K&J Magnetics has some really good magnets for great prices! I found them yesterday, and I'm going to put in an order on Friday.

[Grumples]

I don't know if that gauss cannon really is what you're looking for.  I've tried it, and I can guarantee that I could easily *throw* the ball about twice as far, even though I used several very powerful rare-earth magnets.  If you want to propel it without using explosives, you could work around the limitation using something like dry ice, which can provide explosive caliber pressure, sans exlosives (just let the stuff warm up.  Where do you think all the CO₂ goes?).  After all, it's the high gas pressure created in a typical explosion that makes explosives so useful for this sort of thing.

[Corvettaholic]

I'm scared of dry ice bombs. I wasn't before, until my neighbor and I put some dry ice in... well... I skip the details. Suffice to say it made a really loud sound and tore some really big holes in a container that shouldn't have had holes in it. But I really want to get this magnet idea to work! I know the one they have on scitoys won't throw anything very far, but I think it can be modified to work a lot better. Better as in more firepower. I'm thinking all its gonna take it much stronger magnets, and more acceleration stages. The more stages and magnetic strength, the more potential energy I have to work with. Just gotta get it up to the level of a rifle bullet or something...

[arnyk]

Ok wow what you're talking about would require a very strong magnet.  I would say any standalone magnet wouldn't strong enough...you'd have to go with an electromagnet or something like a solenoid.  Coil it as many times as you can as tightly as you can, and run a huge ass A/C current through it.  Something like those japanese levitating trains, now those things can fly fast.

[Corvettaholic]

Oh I LOVE electromagnets, but I've played enough with those. I really want to get something to work with permanent magnets, and that way I don't have to lug around a power source. Since with permanent magnets I can't change the strength of them, I have to find another way for added kick. Hence I want to make different 'stages' of acceleration, much like a coil gun. But with this design, there are a series of ball bearings which slam into a magnet, releasing the next ball bearing which hits the next magnet, and so forth. Each step along the way will add some kinetic energy, because when one ball bearing is knocked loose, the next magnet will start drawing it which will accelerate it even more. If you check out the scitoys link I posted a bit ago, it will explain it much better than this.

Main thing I want to know is that when I upgrade to much larger magnets, how should I alter the spacing for optimal acceleration. I'll figure out something to handle the magnet smashing problem. When you look at the diagram at scitoys and the video they have, there is no buffer in the receiving end of the magnet. So I'll put something there. Can't be too elastic or squishy, because that will absorb too much kinetic energy, but it can't be brittle either or the shattering problem continues. The buffer needs to be ferrous so it will act as an extension of the permanent magnet. I suppose being dimagnetic would work too.

[constant thinker]

Corvettaholic you always have the coolest posts. That is a very cool idea with all the magnets. That is a cool website. You have so many projects though. You must have money.

[Corvettaholic]

Money? hahahahaha.... no. I am in the army after all. I haven't forgotten about all these projects, they're just all on 'hold'. What are they waiting for? Money. I'm having issues with my house refinance, but once I get that hammered out I can finally begin one of these projects. The last project I did was experimenting with the best way to atomize gasoline out in the desert...

[hafford]

how to reverse the pularity of an electromagnet???