Magnets Under Water
Most recent answer: 10/22/2007
- taylor (age 13)
Watertown Middle School, MA, USA
Basically, the force between two magnets depends on how far apart they are and what angles they're turned at. Of course, if there is something else around exerting forces on the magnets, you might lose track of the direct force between them. That happens if there's, say, a piece of iron between them. They magnetize the iron, so there's now another magnet around. Whether it makes the net force on each magnet bigger or smaller depends on how they are arranged.
Since water is almost completely non-magnetic, it just doesn't make any significant extra magnetic force on the magnets. All you get is the same force there would have been if they were in air or in a vacuum.
(published on 10/22/2007)
Follow-Up #1: magnet in water
- david (age 13)
(published on 10/22/2007)
Follow-Up #2: magnets in hot water
- Andrew (age 12)
Boston, MA, United States
It wouldn't make much difference because water has very little magnetism whether hot or cold. If the water were hot enough, however, it could cause the "permanent" magnets themselves to weaken. That's because when heated the magnetic domains can rearrange, and they tend to cancel each other out. When very hot, the magnetism of the magnetic material collapses altogether, but for ordinary permanent magnets that takes heating far above the boiling point of water.
(published on 10/28/2007)
Follow-Up #3: water magnetism
- Aleasha (age 14)
There's a nice Wikipedia article on "diamagnetism" , which mentions the diamagnetic strength of water. It affects the strength of the magnetic field by about 0.001%, which is a very small effect.
(published on 04/09/2008)
Follow-Up #4: diamagnetism
- Augh (age 13)
(published on 04/17/2008)
Follow-Up #5: magnet in water
- Margarita (age 12)
(published on 04/20/2008)
Follow-Up #6: magnets in hot water
- Brynn (age 12)
If you were checking how quickly a paperclip or something like that moved toward the magnet, it might move more quickly in hot water because that is less viscous (frictiony) than cold water.
If you were checking how far away the magnet could get and still pick up the clip, then I don't understand the result.
(published on 05/02/2010)
Follow-Up #7: Magnets and paper clips in water
- Camilla (age 16)
If the density of the object is 1, then the effective weight is zero, and the object floats. You might try to see if your results with the paper clips are consistent with the 12.5% prediction. Let us know what you find.
(published on 06/01/2010)
Follow-Up #8: Do conducting solutions affect magnetism?
- Alex Avery (age 15)
Huntsville, Alabama, United States
There is one general effect of conductivity on magnetism. If the magnetism is changing over time then it stirs up eddy currents in the conductor. Those eddy currents create magnetic fields which tend to cancel the changes in the field in the region of the conductor. That's how ordinary metal boxes can shield their contents from high-frequency magnetic fields. However, with the exception of superconductors, this sort of shielding doesn't work for dc fields.
What would happen if you had magnetic ions (e.g. H+or Mn++) in the solution? Even then they wouldn't change the magnetism much, because each one aligns very little in big fields at room temperature. That's true even for Mn++, with an electronic moment, and even more true for H+ with just a nuclear moment. So the magnetic fields are changed very little by these solutes. Very little is not, of course, quite the same as zero. MRI machines work by sensing tiny magnetic changes, primarily in H+ nuclei.
(published on 02/19/2011)
Follow-Up #9: Magnetic surface tension in water? Or a layer of baloney?
- Mike W (age 61)
(published on 02/22/2011)
Follow-Up #10: small magnets feel the earth's field
You can see that the small magnets in compasses are affected by the Earth's field. That's what lines them up. How small could a magnet be and still line up pretty well? The magnetic alignment is disrupted by random thermal jiggling, as molecules bounce off the little magnet. In order to line up pretty well, the magnetic alignment energy has to be about as big as the thermal energy scale. At room temperature that's around 4*10-14 ergs. The magnetic alignment energy is the product of the field and the magnetic moment of the magnet. The Earth's field is around a half a Gauss. That means that you need a magnetic moment of around 10-13 emu. A single electron can contribute about 10-20 emu. So you need about 107 electrons involved, at about one electron per atom for a typical magnet. That's a really tiny magnet, only 10 million atoms.
Who would use such a tiny magnet in the ocean? Why, a magnetotactic bacterium, of course. These bacteria use tiny magnets to help orient themselves. The smallest magnetic crystals used are only modestly bigger than the minimum size we calculated.
(published on 03/13/2011)
Follow-Up #11: magnets in liquids
- noah (age 14)
louisville, KY, USA
(published on 05/08/2011)
Follow-Up #12: liquids and magnetism
- Ben Dolder (age 16)
Some liquids, like liquid oxygen, are rather more strongly paramagnetic. You can easily see it getting pulled into a magnetic field. The reason is that every molecule contributes to the paramagnetism. In those aqueous solutions only a small fraction of the material is contributing.
(published on 11/13/2011)
Follow-Up #13: magnetic elements
- Vernon vouga (age 26)
Anchorage ak us
All materials are at least slightly affected by magnetism. When you say "create magnetism" I think you mean ferromagnets, materials that form magnetized domains with appreciable fields at a distance. In addition to iron, there are 3 other elements that form ferromagnets at room temperature: nickel, cobalt, and (depending on how cool the room is) gadolinium. In addition, several others go ferromagnetic at lower temperatures, as described in this link: .
In addition to these elements, there are countless alloys and compounds that are ferromagnetic.
(published on 06/05/2012)
Follow-Up #14: magnets in cold or hot water
- Caleb (age 11)
If you put a magnet in some really cold fluid (say liquid helium) its magnetism will probably go up just a tiny bit. If you put it in some very hot fluid (maybe very hot steam) it will lose its magnetism altogether.
(published on 04/29/2013)
Follow-Up #15: Curie point of dysprosium
- Gareth (age old)
Carpentersville, Illinois, USA
Yipes, thanks for the correction!
(published on 08/09/2013)
Follow-Up #16: why answer questions?
- Ryan Beyer (age 100)
Why are those two answers exclusive of each other?
(published on 06/09/2015)