Message-Id: <v01540b06af3a6cfa91a0@[192.174.2.173]>
Date: Wed, 26 Feb 1997 14:55:15 -0800
To: pinhole@exploratorium.edu
From: pauld@exploratorium.edu (Paul Doherty)
Subject: Re: static forces
Hi Karen
Some thoughts on you static questions.
1.1) Why/how is it that plastic is such a good material for generating static
AND at the same time good for insulating electrical wires? Why does it
collect the forces so well, and why if I can feel and see the static, why
not the electricity through insultated wires as well?
Metals which are electrical conductors also acquire an electric charge
when rubbed (for example aluminum airplanes are charged when they are
rubbed with air during flight.) However when we hold the aluminum to rub
it, the charges run off the aluminum as fast as they are created because it
is a conductor.
Plastics that are insulators are charged by rubbing them and then the
charge stays put, because they are insulators.
A wire carrying electric charges inside an insulating wire cover is
uncharged. any given volume of the wire contains the same number of + and -
charges, it just happens that the - charges are in motion.
2) Can static electricity with a charge card, ie rubbing it to induce
static also destroy its magnetic charge?
No There is no way the static electric charge will alter the magnetic poles
recorded in the charge cards. Magnetic poles can olnly be reversed by
magnetic fields not by electric fields. The magnetic fields made by rubbing
a charge card are too small to change the magnetic poles.
3) When hair is standing up with a static charge, is it "on end" because it
is attracted to some positive charges in the air?
The hair stands up because it is all charged ( say it is all negatively
charged.) The negative charges on some hair repels the negative charges on
other hair. So hair stands on end not because it is attracted by positive
charges above, but because it is negative and is repelled by negative
charges below.
4) Does a balloon charged with static electricity forces attract only those
particles that are polar enough or small enough to react? So the static
actually attracts the more positively charged "side" of the salt crystal?
But pepper? Polar? Why not sugar?
A charged balloon ( say negative) takes an uncharged and non-polar pepper
grain and pushes the negative charges in that grain to the far side while
attracting the positive charges to the near side. The pepper becomes
polarized (although still made of non-polar molecules) The negative balloon
then attracts the nearer positive side of the pepper more than it repels
the more distant negative side. However the force is small compared to
gravity so only light grains can be lifted against gravity. Which is why
salt and pepper are lifter but larger sugar grains are not.
I hope these help,
If my answers add to your confusion keep asking perhaps I can do better a
second time.
Paul Doherty