Magnetic Experiments

[ecuabron]

Hi, I would like to make a "floating" thingy experiment, I'm new to this forum but I've always been curious to science, I have two ring shaped magnets (found em in the trash) one of them is pretty strong and the other not so much, So any advice? I'd like it for a "desktop ornament", not my PC desktop of course..

[YT2095]

get an eBay account and buy some Pyrolytic Carbon

[Mr Skeptic]

With two magnets, you could only build an unstable configuration. You would need something to prevent them from just rotating and sticking together, like a stick so you can stack them on top of each other. I don't think that is what you wanted, but it is about all you can do.

[Rocket Man]

where are the poles of the ring magnets? you can probably get something to float over it.

if it's a speaker magnet then its a definite yes. the poles go straight through the centres making something of a pocket in the field strength.

 

the biggest problem is getting the floating part balanced. as Mr Skeptic mentioned, magnets have a tendancy to flip.

some comercial ones use a magnetic gyro. and a motor of some sort.

(essentially a magnetic bearing)

[alan2here]

You can't get magnets to levitate above other magnets no matter what you do with only magnets unless you put some power in to spinning one or more of them.

 

Pyrolic (yes, I know iv'e spelt it wrongly) graphite will require neodymium iron boron (NIB for short) magnets in a cirtain configuration, it will also require the Pyrolic graphite to be set up correctly and it is expensive stuff, look in goggle video if you are really interested.

 

Also alternating current coils of wire can be set up to levitate stuff, this is also however far from simple to set up.

 

There are other ways like superconductors but this is getting really really hard now.

[Rocket Man]

a non ferro magnetic weight hung from one magnet will suffice as a static balance.

[John Cuthber]

No, it wont.

You can get things to float stationary in mid air but you need strong magnets and strongly diamagnetic materials like graphite, bismuth or superconductors.

You can also use the gyroscope effect to stabilise a system. As has been said, a lot of the commercial "toy" versions are based on this principle.

What you cannot do is have a stationary system without diamagnetism that floats.

http://en.wikipedia.org/wiki/Earnshaw's_theorem

[Rocket Man]

surprising. thanks for that.

a voliation of earnshaws theorem would be a string to the base of the magnet. but then why not use a dynamic system.

[John Cuthber]

Perhaps we have different versions of the idea of floating, but "tied up with a bit of string" doesn't feature in mine.

[Rocket Man]

then perhaps tied down is the term you're searching for?

needless to say, dynamic systems are always cooler.

[Mr Skeptic]

No, it wont.

You can get things to float stationary in mid air but you need strong magnets and strongly diamagnetic materials like graphite, bismuth or superconductors.

You can also use the gyroscope effect to stabilise a system. As has been said, a lot of the commercial "toy" versions are based on this principle.

What you cannot do is have a stationary system without diamagnetism that floats.

http://en.wikipedia.org/wiki/Earnshaw's_theorem

 

Earnshaw's theorem assumes that only electrostatic interaction is holding things in place (and that they are not moving). This is not going to be the case, because you also have the ground holding the bottom magnet in place, which is not an electrostatic force. Rocket Man's suggestion to use a non-ferromagnetic hanging thing to prevent the magnet from flipping just might work. It would need to supply enough torque without being too heavy, and there would have to be the dip of magnetic field strength in the middle.

[alan2here]

The dip is an interesting phenominem however you are not going to break any fundamental rules of physics with it. You can levitate a ball bearing in a tube with it, however here the usually plastic or glass tube is also holding the ball bearing in place.

[Rocket Man]

earnshaws theorem applies to any force with an inverse square taper to the field. so that's gravity, electrostatics and magnetism. there's more but these are the ones that apply.

earnshaws theorem only works because the "dip" in the feild strength i mentioned isn't perfect. it's what's called a saddle point. the levitating magnet will slip off to one side if it's rotationally stable.

 

earnshaws theorem also helps explain the "ice pale effect" if you have a charged sphere, any charge within in the sphere experiences zero net force.

[recursive]

United Nuclear (unitednuclear.com) sells a good kit for this. It's 30 bucks, and it gives you some fantastic bismuth slabs and all the necessary magnets and stuffs.

[alan2here]

The graphite\bistmuth expement runs for a long time only slowing down rotation by air resistance, It would be intresting to know how long it would take to (lets say half in speed of rotation) if it was done in a vacume (or a tube that had no air inside it), partucuarly intresting as you could keep speeding the roatation up from outside (lets say shining light onto it, also involves black and reflective surfaces) and almost nothing would be ever slowing it down (only eddy currents in neerby paro\fero magnetic objects).