# Levitation of objects by a magnetic field ?

1. Aug 7, 2007

### phy-79

levitation of objects by a magnetic field ????

how is it done?
does this happen when opposite (charged) field come in contact?
i'hve not understood it properly so pls xplain.

2. Aug 7, 2007

### CraigD

Opposites attract, likes repell.

That is each magnetic field has a North[N] and South pole, two magnets connect NS or SN. If you try to make a like connection, SS or NN they repel each other, that is if they are laying on a table and you push one magnet towards the other, the other will slide away, or spin to match NS or SN.

As far as levitation, it is a mater of stopping the magnets from flipping or sliding away. You can see toys that have a stick with dougnut shaped magnets that levitate abouve each other on the stick.

CraigD, AMInstP
www.cymek.com

3. Aug 7, 2007

4. Aug 8, 2007

### phy-79

i'm sorry.i was just stupid.(abt the opposite poles repel)
yeah now i get it. thanks.

5. Aug 8, 2007

### da_willem

Indeed you can have the poles of two magnets oppositely directed repel each other as in these toys. The stabalizing factor here is a large angular momentum, which you have to apply by making the toy spin very fast. I got one myself, but I'm not so skilled in using it however...:grumpy:

One can, however also magnetically levitate electrically conducting objects by using a very high frequency induction coil. By suppling the coil with a very high frequency current, a rapidly changing magnetic field, i.e. an electric field is induced which can induce currents in the electrically conducting object, e.g. a droplet of mercury or a plasma. These currents are opppositely directed to the currents in the coil and thus are repelled by the coil, which can be used to levitate the object.

Or alternatively the Lorentz force on the conducting object JxB can be written as the sum of 'Maxwell stresses' and a 'magnetic pressure' B^2/4mu, the latter of which pushes the object away.

As a possibly added benefit the currents developing in the conducting object can, by Ohmic dissipation, in certain circumstances melt the object. This levitation melting is used for quite some time now for highly reactive substances e.g.

6. Aug 8, 2007

### mgb_phys

Even frogs http://www.hfml.ru.nl/levitate.html [Broken]

Last edited by a moderator: May 3, 2017
7. Aug 8, 2007

### CraigD

A nother way to combat the stability problem is to spin the floating magnet.

CraigD, AMInstP
www.cymek.com

8. Aug 12, 2007

### GDogg

It's important to note, though, that while having angular momentum is a necessary condition, it's not sufficient. It can be shown that if the angular momentum vector is always vertically oriented, the configuration is unstable. The levitating magnet needs to precess as well.

PS: I've used that toy too. You're right, it's quite hard to spin it the right way! :tongue:

Last edited: Aug 12, 2007