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'[OT] Static electricity question'
2010\01\05@152958 by

I'm a bit confused about this.  If I walk across a carpet with the right kind of shoes and mostly in winter time, when I touch a metallic doorknob there is a spark between me and the metal, and also a bit of a shock for me if I'm not expecting it.

That's understandable.

But I noticed that when I pet one of my cats then touch its ear, the cat gets a bit of a shock.  That seems ok to me.

But if I pet one cat enough to build up a charge and then touch the ear of another cat, nothing happens.  I most certainly wrongly connected with petting a cat to sliding my shoes across the carpet. What then explains this?

Thanks,
Lindy

And happy 2010.

When you pet the cat the charge transfers from you to the cat (or the
cat to you - I forget which).

This results in a high potential between you and the cat.  If you are
touching something else, that something else also gets your charge,
relative to the cat.  Cats don't transfer charge to other cats easily,
so your potential with respect to the other cat isn't as high
(although it should be higher than normal, it's not enough to zap
them).

When you shuffle your feet on the carpet, the flooring, and thus the
whole house, is charged with respect to you.  The doorknob acts as a
grounding point for the house.

Note that the carpet is an insulator, and so is the cat fur.  The
charges don't equalize until you touch a conducting member of the
house or cat, or get near enough that the air breaks down and
transfers the charge for you.

If you get everything at the same potential, though (touch the cat's
noses and the door knob at the same time, or repeatedly until
everythign averages out) and then place yourself at a high potential
(shuffling, petting a cat, etc) then you will be at a higher (or
lower) potential than everything.  It's just that the difference will
be 2x higher/lower for the thing you stole the charge from than it is
with the things you didn't steal the charge from.

So you can still zap the other cat, but only at about half the zap you
would get with the original cat.  This would probably be best detected
at the end of the cat's nose, and with your more sensitive pinky or
ring fingers than your index finger.

If you rub both cats together then all bets are off.

On Tue, Jan 5, 2010 at 3:29 PM, Lindy Mayfield
<lindy.mayfieldssf.sas.com> wrote:
{Quote hidden}

>

:: f you rub both cats together then all bets are off.

I thought that was boy scouts?  :)
--
cdb, colinbtech-online.co.uk on 1/6/2010

Web presence: http://www.btech-online.co.uk

Hosted by:  http://www.1and1.co.uk/?k_id=7988359

On Tue, Jan 5, 2010 at 8:29 PM, Lindy Mayfield
<lindy.mayfieldssf.sas.com> wrote:
> But if I pet one cat enough to build up a charge and then touch the ear of another cat, nothing happens.  I most certainly wrongly connected with petting a cat to sliding my shoes across the carpet. What then explains this?

There is an open circuit on the other cat :-)

Tamas

>
> Thanks,
> Lindy
>
> And happy 2010.
>
>
>
Tamas Rudnai wrote:
> But if I pet one cat enough to build up a charge and then touch the ear of
> another cat, nothing happens. I most certainly wrongly connected with
> petting a cat to sliding my shoes across the carpet. What then explains
> this?

There is an open circuit on the other cat :-)
===

Or maybe, when you pet the cat, you charge the cat but yourself remain at a
"neutral" (ground) potential? Try petting cat #1, then touching its ear with
cat #2's paw to confirm this theory. Or, use an electroscope.

Vitaliy

PS Try not to get too carried away with your animal experiments.

I don't know what kind of cat you guys have, but if I tried these
kinds of experiments with mine he would give me the "look of death"
and promptly scratch me :)

Actually, the cat I had as a kid was considerably more tolerant and
would probably have let me grab her paw and touch it to another cat.

Sean

On Wed, Jan 6, 2010 at 4:36 AM, Vitaliy <piclistmaksimov.org> wrote:
{Quote hidden}

> -
> But if I pet one cat enough to build up a charge and then touch the ear of
> another cat, nothing happens.  I most
> certainly wrongly connected with petting a cat to sliding my shoes across the
> carpet. What then explains this?

The electrostatic charging process is a relative energy exchange between two
objects (which can be rubbed against each other for example). If the two objects
are isolated then the two objects will each build up a charge against each other
(*and* against ground), with voltages proportional to their capacitances and
*equal* charges of opposed sign. The relative signs of the charges depend on the
nature of the rubbed materials.

If the initially insulated charged objects are later touched to each other, then
they discharge such that they have equal potential again. If any one of the
objects separately touches ground or is touched by a grounded object or by a
non-charged object which can accept charge, they will each be capable of being
zapped or to zap, separately.

If one of the objects was grounded while the charging took place then only the
*other* object will be charged wrt. ground. The first object (cat owner) will
carry no charge wrt ground and will not draw a spark from a doorknob etc.
His/her charge will have been grounded slowly during the petting, to ground. The
cat, however, will carry the charge and may be zapped later.

If the cat was on the floor when it was stroked and the owner on an insulated
sofa, then the cat will carry no charge, but the owner might get zapped when
touching the doorknob *or* the cat's ear/nose, as the owner will be charged vs.
ground.

It is also possible for the owner and the cat to get separate zaps after leaving
the insulated petting ground, both against ground, or against each other.

I have never built up a charge against a cat, but anyone with such problems
should look hard at humidifiers, either natural (potted plant, aqarium) or
machine ;)

Peter

Peter wrote:
> I have never built up a charge against a cat

Cats in your neck of the woods normally are short-haired. To
experiment you need to find some long-haired cat. Folks who move from
North often bring that kind of "Siberian" cats.
http://en.wikipedia.org/wiki/Siberian_(cat)
On Thu, Jan 7, 2010 at 10:24 AM, Marechiare <marechiaregmail.com> wrote:
> Cats in your neck of the woods normally are short-haired. To
> experiment you need to find some long-haired cat. Folks who move from
> North often bring that kind of "Siberian" cats.
> http://en.wikipedia.org/wiki/Siberian_(cat)

To avoid ESD during peting the cat, you need to get a special one,

http://en.wikipedia.org/wiki/Sphynx_%28cat%29

Tamas

> -
Canadian ? - looks more Brazillian to me !!

RP

2010/1/8 Tamas Rudnai <tamas.rudnaigmail.com>:
{Quote hidden}

>> --
>> North often bring that kind of "Siberian" cats.
>> http://en.wikipedia.org/wiki/Siberian_(cat)
>
> To avoid ESD during peting the cat, you need
> to get a special one, like the Canadian :-)
>
> http://en.wikipedia.org/wiki/Sphynx_%28cat%29

Great, but how do they manage to survive Canadian winter?

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