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Levitating frog




I thought the levitating frog rumor was a hoax. Nope, just diamagnetism
and very strong fields.

http://www.hfml.sci.kun.nl/hfml/levitate.html

If you have a neodymium magnet, you can repel a falling stream of water,
or cause a "dimple" to form on the surface of a water pool. See
http://www.eskimo.com/~billb/neodemo.txt

I haven't tried it, but I bet you can use an NIB magnet to visibly move a
piece of Bismuth metal hanging by a thread. This might even work with an
ice cube. (or a frog!)

=2E....................uuuu / oo \ uuuu........,...........................=
=2E.
William Beaty voice:206-781-3320 bbs:206-789-0775 cserv:71241,3623
EE/Programmer/Science exhibit designer http://www.eskimo.com/~billb/
Seattle, WA 98117 billb@eskimo.com SCIENCE HOBBYIST web page


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Molecular Magnetism and Levitation.
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(The Frog Which Learned to Fly)
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Seeing is believing:
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A little frog (alive !) and a water ball levitate inside a =D840mm vertic=
al
bore of a Bitter solenoid in a magnetic field of about 16 Tesla at the
Nijmegen High Field Magnet Laboratory.
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[LINK]
[LINK]
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(Click on the images to get a larger one)
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The image of a high-temperature superconductor levitating above a
magnet in fog of liquid nitrogen can hardly surprise anyone these days
it has become common knowledge that superconductors are ideal
diamagnetics and magnetic field must expel them. On the other hand,
the enclosed photographs of water and a frog hovering inside a magnet
(not on board a spacecraft) are somewhat counterintuitive and will
probably take many people (even physicists) by surprise. This is the
first observation of magnetic levitation of living organisms as well
as the first images of diamagnetics levitated in a normal,
room-temperature environment (if we disregard the tale about Flying
Coffin of Mohammed as such evidence, of course). In fact, it is
possible to levitate magnetically every material and every living
creature on the earth due to the always present molecular magnetism.
The molecular magnetism is very weak (millions times weaker than
ferromagnetism) and usually remains unnoticed in everyday life,
thereby producing the wrong impression that materials around us are
mainly nonmagnetic. But they are all magnetic. It is just that
magnetic fields required to levitate all these nonmagnetic materials
have to be approximately 100 times larger than for the case of, say,
superconductors.
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Whether an object will or will not levitate in a magnetic field B is
defined by the balance between the magnetic force F =3D M nabla B and
gravity mg =3D rho V g where rho is the material density, V is the
volume and g =3D 9.8m/s2. The magnetic moment M =3D ( chi / =B50)VB so t=
hat
F =3D ( chi /=B50)BV nabla B =3D ( chi /2=B50)V nabla B2. Therefore, the
vertical field gradient nabla B2 required for levitation has to be
larger than 2=B50 rho g/ chi . Molecular susceptibilities chi are
typically 10-5 for diamagnetics and 10-3 for paramagnetic materials
and, since rho is most often a few g/cm3, their magnetic levitation
requires field gradients ~1000 and 10 T2/m, respectively. Taking l =3D
10cm as a typical size of high-field magnets and nabla B2 ~ B2/l as an
estimate, we find that fields of the order of 1 and 10T are sufficient
to cause levitation of para- and diamagnetics. This result should not
come as a surprise because, as we know, magnetic fields of less than
0.1T can levitate a superconductor ( chi =3D -1) and, from the formulas
above, the magnetic force increases as B2.
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The water and the frog are but two examples of magnetic levitation. We
have observed plenty of other materials floating in magnetic field -
from simple metals (Bi and Sb), liquids (propanol, acetone and liquid
nitrogen) and various polymers to everyday things such as various
plants and living creatures (frogs and fish). We hope that our
photographs will help many particularly, non-physicists to appreciate
the importance of magnetism in the world around us. For instance, it
is not always necessary to organize a space mission to study the
effects of microgravity some experiments, e.g. plants or crystal
growth, can be performed inside a magnet instead. Importantly, the
ability to levitate does not depend on the amount of material
involved, V, and high-field magnets can be made to accommodate large
objects, animals or even man. In the case of living organisms, no
adverse effects of strong static magnetic fields are known after all,
our frog levitated in fields comparable to those used in commercial
in-vivo imaging systems (currently up to 10T). The small frog looked
comfortable inside the magnet and, afterwards, happily joined its
fellow frogs in a biology department.
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A.K. Geim, H.A. Carmona, J.C. Maan=20
_________________________________________________________________
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* Go to the HFML Home Page.=20
_________________________________________________________________
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Last updated on 14-feb-97 ln