Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Invisible Force Fields, Ionized Air, and Human Charge

Learn more physics!

Most recent answer: 10/22/2007
Q:
I read an article at this website: http://www.esdjournal.com/articles/final/final.htm It was EXTREMELY interesting. You have to read it to respond to my questions. a) Is it possible to repel humans with some type of invisible force (electric, magnetic, etc...)? b) What is "ionized air" and how (if possible) can it be created and/or contained? How long will it stay ionized? c) Do humans have a specific electric charge (pos. or neg.)? A magnetic charge (north or south)? Thanks a lot!
- Courtland (age 15)
GA, USA
A:
Hi Courtland,

Also another interesting article. Indeed, the polypropylene processing plant seems to have been generating very high voltages by transporting their plastic film from one spool to another and handling it on various rollers, and the web site in fact says that steps were taken at the plant to try to reduce the buildup of static voltages. Depending on the capacitance of the setup and the voltage, a person doing experiments like the one described can receive a very nasty shock! The shocks I get when rubbing my feet on the floor and touching something grounded (like a switchplate on the wall) are painful enough. With a big piece of machinery like that, someone can get seriously injured by a static electrical discharge.

The answers to your questions are:

a) I suppose so, but the details in the article do not sound plausible, and it would be easy enough to defeat such a force field. When people touch a high-voltage source, they become charged. Like charges repel and opposites attract, and so charging up a person will make him repel other objects with the same charge. It turns out that the individual hairs on a person will also be charged with the same sign, they will repel each other, and one's hair will stand on end when charged up. You can see this effect with a little girl charging herself up with a Van de Graaf generator

Girl with a Van de Graaf generator with hair standing upNow it turns out that the Coulomb force one feels is inversely proportional to the square of the distance between the two charged objects. Various factors make the distances even more complicated. People are made largely out of saltwater and we therefore conduct electricity rather well. If you are charged up and come near another charged object, the charges will repel, and many will simply flow to other parts of your body farther away from the repelling charge. One may feel a repelling force -- not a solid wall-like sensation, but rather a soft, cushiony sensation should be felt.

And yes, the force can be defeated simply by allowing the charge on the person to escape. If the person carries a wire that is connected to the ground, then charge may flow freely away and the force experienced may be much reduced (in this case it may even change sign, becoming attractive).

Electric and magnetic forces are used routinely to propel charged particles -- inside television tubes, particle accelerators, and magnets for scrap metal recovery. It's just that they work poorly on people because we aren't very magnetizable (being made mostly of water) and we can use our smarts to get rid of excess charge buildup.

b) Ionized air consists of air with some fraction of the molecules either missing electrons or having extra electrons. It can be created by passing a current through the air (lightning does this, and sparks in general will ionize the air). Air does not normally conduct electricity very well for electrons to come and balance out the ions' charges and so ions may persist for a few seconds and perhaps even longer. It is not easy to contain ionized air since the ions exchange electrons with the material of whatever bottle you put it in. I suppose non-conductive bottles will work the best --something like teflon should keep the ions from de-ionizing the most. It will be hard to put a lot of ions of the same charge into a bottle however because like charges repel and they will want to fly apart. Placing an equal number of positive and negative ions together restores electrical neutrality, but it is only a matter of time (and sometimes very short!) before the ions recombine and become neutral themselves.

c) Humans do not have any particular electrical charge. We can charge ourselves up to be positively charged or negatively charged by scuffing our feet on the floor, by petting a cat on a dry day, by rubbing some kinds of plastic (a comb, for instance) or a rubber balloon in our hair. But we can just as easily discharge ourselves (ouch!) by touching something that conducts and has a different charge (like the Earth or something electrically connected to it, like water pipes).

As far as we know, nothing has a magnetic charge. There does not seem to be any evidence for the magnetic equivalent of an electrical charge, although the theories of physics are as far as I know consistent both with and without magnetically charged objects (we might learn some important things if we ever did observe a particle with a magnetic charge). These hypothetical particles are called "magnetic monopoles" and may be either North or South. All magnets we know of are at least "dipoles" -- they have a North and a South pole, and sometimes more than one of each. No monopoles have been observed, in spite of intense efforts to look for them. People also have essentially no magnetic dipole (the sort of paired North-South poles that ordinary magnets have.)

Tom

(published on 10/22/2007)

Follow-up on this answer.