MadSci Network: Biochemistry

Re: How does the human body act like a magnet

Date: Wed Feb 9 13:41:21 2000
Posted By: Todd Holland, Grad student, Biophysics, University of Illinois at Urbana-Champaign
Area of science: Biochemistry
ID: 949954962.Bc

Well Casey,
I hate to disagree with your Mom, but since you did ask I will reply. The 
human body as a whole has practically no magnetic properties. And even if 
your hand was acting as a magnet, it wouldn't produce the type of motion 
that you are describing. 

Try this experiment. Take your threaded needle and hold it over a real 
magnet. If the magnet is strong enough for the needle to feel its pull, it 
should be pulled towards it uniformly and not sway. Any swaying or movement 
of the needle is due to the unsteadiness of the hand holding it, and 
currents in the air. If you hold your hand out flat in front of you, not 
resting it on anything, you'll notice that it is never truly still. It is 
always moving a little. A psychologist might also tell you that if you want 
the needle to sway one way or the other, you might subconsciously cause it 
to, but I'm not a psychologist. All I can tell you is that it is not due to 
any magnetic properties of the human body. 

Another experiment to try is to hang the needle from something steady. It 
still moves a little, because their are small currents in the air around 
it. Try blowing gently on it from a distance. Notice how easy it is to make 
it move. Also try putting your hand under it, while it is hanging from 
something. If you are very careful to be still and not breathe on it, 
you will notice that the swaying of the needle remains unchanged by the 
presence of your hand. It was swinging before, and it continues to sway 
more or less randomly due to air currents. 

Then hang the needle down inside of a jar or something that shields it from 
air currents. You will have to cover the mouth of the jar. I taped the 
thread to a ruler, then laid the ruler over the open mouth of a glass 
bottle, with the needle hanging down into it. If the jar was on a sturdy 
surface, the needle eventually stopped swaying to any amount that I could 

Having said all of this however, some of the individual atoms in the human 
body do have magnetic properties. Normally they are all randomly oriented 
so that there is no overall magnetic field associated with them, but their 
magnetic properties can be used by scientists and doctors to "see" inside 
the body using a technique called Magnetic Resonance Imaging, or MRI. In 
MRI, a very powerful external magnetic field is used to cause all of the 
magnetic atoms in a region of the body to rotate so as to align their 
magnetic fields with an applied external field. Then radio waves are beamed 
at the part of the body you want to look at. Some of these are absorbed by 
the magnetic atoms (mostly hydrogen atoms in water molecules) in that 
region, causing them to flip their magnetic field. Later, these atoms flip 
back to their original orientation, and give off more radio waves. These 
radio waves can be detected by sensitive instruments and used to "see" 
inside of the body. 

Here is a website describing MRI:

You can also find other websites on it by searching for MRI or Magnetic 
Resonance Imaging using Yahoo or some other search engine on the Internet. 

Using MRI, doctors can look inside of the body for tumors and other things, 
and scientists can conduct research on changes that go on in the brain 
during thinking, and in muscles when they are contracting. They could also 
probably look and tell what sex a baby in the mother's womb is, but usually 
use a technique called ultrasound is used to do this, which uses sound to 
see inside the body.

So you see, you can use magnetic properties to tell what's going on inside 
your body, it just takes a little more expensive equipment than a needle 
and thread. And although MRI can't tell you what sex your kids will be in 
10 or 20 years, it can tell you a lot. I hope you find it as exciting as 
needle and thread fortune telling. I know I do. Thanks for the question.


Todd Holland
Mad Scientist and Graduate Student in Biophysics
at the University of Illinois at Urbana-Champaign

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