# Very basic physics question

1. Feb 16, 2013

### cashflow

The most physics I ever took was Physics C in high school (physics with calculus). I have now forgotten almost all of it, with remnants of memory here and there (Biot-Savart law comes to mind). Anyway, this not a homework question. I am trying to trap some metal particles at a particular location in space (some arbitrary location). The particles are blowing all over the place in a cube, and I need to concentrate them at a particular location. Now, these particles have a net force in a magnetic field. Concept wise, I thought I could just stick two magnets (with the north poles facing each other) at opposite sides of the cube. In practice, the particles still whiz around and fail to collect in the middle. So, now I'm sending an SOS to the physicists-- how can I trap these metal particles in the middle (using an electromagnet if necessary)?

This is purely a conceptual question. There are no dimensions or whatever (the cube has an arbitrary side length). I can blow around as many particles as I want in the glass cube (using a small fan). I just want the stuff to collect in the middle. So, how can I position these external magnets? Oh, and the particles are iron.

Thanks :D

Last edited: Feb 16, 2013
2. Feb 16, 2013

Staff Emeritus
I don't think you can. The iron will be attracted to the pole face; you want the iron going to where the pole face isn't.

3. Feb 16, 2013

### cashflow

What if I do some kind of Penning trap? Would that work on iron (I read somewhere that iron can behave like ions, which didn't make sense)? Or perhaps some other molecule? Although I doubt I can recreate something complex looking like a penning trap with household electromagnets...

So it's not possible to get any molecule to collect at some location using electromagnets?

Please enlighten me, o smart ones

4. Feb 17, 2013

### CWatters

If they are iron what's wrong with using one very strong magnet directly under where you want them to collect? I imagine they may stick to the glass some short distance away (due to friction) but perhaps vibrating the glass would fix that. Perhaps make the bottom of the box funnel shape with the magnet at the bottom?

I suppose there might also be a way using sound...

Last edited by a moderator: Sep 25, 2014
5. Feb 17, 2013

### cashflow

I need to "trap" the particles at the center of the cube, and the cube cannot have any other object besides the iron particles (or other particles/molecules) Well, I'll try and think of something. So no one knows any other way? The acoustic tweezers were pretty cool though, but does not work for my situation :\

6. Feb 17, 2013

### my_wan

There's only way I can think that might work, and requires a lot fine tuning even if it would work. Mechanical interference is likely to make it too chaotic to be feasable. You might try placing an electromagnet on each side of the cube and switching them on and off at the right frequency to pull the iron back toward the center. If timed right one magnet pulls them past center, then before reaching the wall turn that magnet off and turn the magnet on the other side on.

It actually looks like a lost cause, but you can try.