Static electricity question
Conase
to which I did NOT have an answer and about which I had often wondered .
If you are in a LIGHTNING storm or near a DOWNED POWERLINE while in your car,
it is always said to STAY IN the car and avoid touching anything metal. The car
is supposed to "insulate/protect" you from the electricity.
We had a backhoe operator at my school who was saved by the RUBBER WHEELS when
the blade hit 2-3 inch feeder cables NOT on the plans from 1903. The
electricity MELTED the substantial steel finger off the blade.
Recently in the news people have been advised to TOUCH the top or any metal
part of the car when exiting to AVOID generating a STATIC electricity spark
based on touching the seats with their winter clothing. Diane Sawyer on GMA ran
the tape of a man setting himself on fire due to static electricity when
refueling. They then provided LIVE demos to show how this could happen.
WITHOUT GETTING HUNG UP ON DETAILS ABOVE - THE QUESTION I COULD NOT ANSWER WAS
:
How can "touching any metal part" of the car DISCHARGE static electricity if
the TIRES are INSULATING it from the ground ?
++++++++++++++++
Years ago at toll booths there used to be some flimsy wires that would touch
the BOTTOM of the cars to discharge static electricity ?
For those of us from the Arthur Fonzarelli days, there used to be rubber straps
that would hang down and touch the ground for static electricity and then flap
in the wind to prevent wear when moving.
In high school physics, I remember the teacher with the piece of fur and the
RUBBER rod generating STATIC electricity to separate the pieces of tin foil in
the jar.
+++++++++++++++++
So I am back to SQUARE ONE :apparently RUBBER is both an INSULATOR and a
CONDUCTOR of electricity, and I STILL have NO ANSWER to my original
presentation question.
TIA
JazzMan
The key thing that you might not be aware of is that modern
car tires have carbon in them which in addition to other things
serves to help prevent a buildup of static electricity on the car.
However, when you slide in and out of a car you don't have an
electrical connection between yourself and the car body, so it is
possible to build up a voltage differential between yourself and
your car. The rubber (or leather) of your shoe soles will prevent
the dissipation of this charge to ground when you get out of the
car, so it will jump to the car when you touch the metal body.
JazzMan
--
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Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
***************************************
Supertimer
>I was giving a presentation on cars the other night when I was asked a
question
>to which I did NOT have an answer and about which I had often wondered .
>
>If you are in a LIGHTNING storm or near a DOWNED POWERLINE while in your car,
>it is always said to STAY IN the car and avoid touching anything metal. The
car
>is supposed to "insulate/protect" you from the electricity.
>
>We had a backhoe operator at my school who was saved by the RUBBER WHEELS when
>the blade hit 2-3 inch feeder cables NOT on the plans from 1903. The
>electricity MELTED the substantial steel finger off the blade.
Insulate is not the right word. Conduct is. Electricity always finds
the easiest path to ground. When lightning hits your car, the
electricity is conducted around the metal body of the car to the
ground because it is an easier path than through air or through
you. The rubber in the tires do little to stop the electricity of that
high a voltage. Even if it did, the electricity will have no problem
jumping from the lowest metal point in the car through the air to
the ground.
Now what happens if there you get out of the car and have contact
with the metal body of the car while your foot is on the ground?
Your body now becomes a better conductor than the tires or the
air and the lightning will go through you. That's why you should
stay in your car.
>Recently in the news people have been advised to TOUCH the top or any metal
>part of the car when exiting to AVOID generating a STATIC electricity spark
>based on touching the seats with their winter clothing. Diane Sawyer on GMA
ran
>the tape of a man setting himself on fire due to static electricity when
>refueling. They then provided LIVE demos to show how this could happen.
>
>How can "touching any metal part" of the car DISCHARGE static electricity if
>the TIRES are INSULATING it from the ground?
Static electricity is also very high voltage so it is able to jump
air gaps for example. It is also very brief. What happens is
that when you exit the car, your clothing rubs against the
seat of the car transferring electrons to you. When you then
touch the metal body of the car, those electrons are returned
to the car. This is a fixed amount of electricity and in this
case the car body is the ground, not the earth.
When you discharge static electricity your car, the car is
ground. When lightning discharges to the earth, the earth
is ground. Lightning is static electricity on a large scale
caused by the atmosphere moving against the surface of
the earth just like your clothing would rub against the seat
of your car.
""pyats\"@tex_as.net"
What saves people in cars is the Faraday Cage effect - NOT the
rubber tires.
The backhoe current went through the blade - fortunately, because
the operator is not in a Faraday Cage.
Static elec. is not the same as current in a wire.
90% of the people that blow up at gas stations are women.
Why? Because women put the nozzle in the tank, get back in the car,
slide their butts around on the seat, accumulate a static
charge, get back out, reach for the nozzle and Ka-Boom!
Men usually just stand there by the nozzle.
Mike Romain
>
> I was giving a presentation on cars the other night when I was asked a question
> to which I did NOT have an answer and about which I had often wondered .
>
> If you are in a LIGHTNING storm or near a DOWNED POWERLINE while in your car,
> it is always said to STAY IN the car and avoid touching anything metal. The car
> is supposed to "insulate/protect" you from the electricity.
Those are two different situations as far as I understand it.
In lightening, the vehicle acts as a 'faraday' cage and the electricity
passes over the top of it to the ground. The tires have enough
conducting materials in them to either allow this high voltage to pass
or the voltage just plain jumps the few inches across them.
Check out the guys that work from helicopters on high voltage power
lines, they wear 'faraday cage' suits of metal mesh.
When a power line hits your vehicle, it acts different, it energizes the
vehicle and the tires have enough insulation to not allow that amount of
power to jump to the ground. So if you get out of the vehicle and touch
both the vehicle and ground at once, blam, you are the conductor for the
power line.
>
<snip>
>
> WITHOUT GETTING HUNG UP ON DETAILS ABOVE - THE QUESTION I COULD NOT ANSWER WAS
> :
>
> How can "touching any metal part" of the car DISCHARGE static electricity if
> the TIRES are INSULATING it from the ground ?
>
> ++++++++++++++++
A static charge is a charge built up on an insulated object basically.
It has a potential to go to a neutral state if grounded.
Same as above for a power line goes for getting out when you have static
issues. If you get out or have one foot on the ground and then turn and
touch the car, you get a static spark because you are grounding the
vehicle with one point of your body.
If you have a positive connection with the vehicle by touching metal
before you get out, the static will dissipate through you shoe over an
area, not an air arc like the first case.
>
> Years ago at toll booths there used to be some flimsy wires that would touch
> the BOTTOM of the cars to discharge static electricity ?
>
> For those of us from the Arthur Fonzarelli days, there used to be rubber straps
> that would hang down and touch the ground for static electricity and then flap
> in the wind to prevent wear when moving.
With the new long life tires they are making these days, I am seeing
more and more of those static straps on cars.
I was told it was because the harder or whatever chemical compound it is
in tires builds up more static than the last generation of them.
>
> In high school physics, I remember the teacher with the piece of fur and the
> RUBBER rod generating STATIC electricity to separate the pieces of tin foil in
> the jar.
>
> +++++++++++++++++
> So I am back to SQUARE ONE :apparently RUBBER is both an INSULATOR and a
> CONDUCTOR of electricity, and I STILL have NO ANSWER to my original
> presentation question.
>
> TIA
Rubber is strange stuff. It is not a perfect insulator and can generate
a static charge as you saw. It also gets mixed with tons of other
things in tires.
Maybe try a google search on it to find out more about it.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
DanS
>How can "touching any metal part" of the car DISCHARGE static electricity if
>the TIRES are INSULATING it from the ground ?
From an un-scientific (un-proven?) standpoint, I thought it was
because the car, being much larger than a person, could absorb and
distribute the static electricity back to ground much easier than a
person can. Driving and being exposed to the ground much more often
than a person allows the car, even with thick rubber-and-air tire
insulation, to slowly distribute the electrical potential back to the
ground. Electricity follows the path of least resistance.
>So I am back to SQUARE ONE :apparently RUBBER is both an INSULATOR and a
>CONDUCTOR of electricity, and I STILL have NO ANSWER to my original
>presentation question.
Insulation doesnt stop the transfer of electricity, it merely hinders
it in a certain direction. If a less-resistant avenue presents itself
(ie grooves in a printed circuit board), then the electricity will
follow that path.
Dan
Robert Hancock
basically, any sufficiently large metal object, even if not connected to
ground, can discharge static electricity from a person because it's a large
"electron sink", so to speak, and the amount of actual charge on your body
is very low. With a power line, however, the amount of charge is much
larger, once the car becomes charged to the voltage potential of the power
line, it has nowhere to go.
As far as the rubber static discharge straps, natural rubber is a very good
insulator, but with carbon put into it, it can become conductive (or at
least conductive enough to remove the small charge from static electricity).
The rubber in the tires has carbon in it too, but I don't think they're
generally conductive enough to have much effect on the charge from a power
line (unless maybe it's a line from one of those really high-voltage
transmission lines, which might be able to spark right over).
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamshaw.ca
Home Page: http://www.roberthancock.com/
"Conase" <con...@aol.commado> wrote in message
news:20030201102542...@mb-fb.aol.com...
John Merrifield
testing certain distributor-less ignition systems, I install a short section
of vacumn line between the coil tower and the plug wire. It conducts
beautifully and I can then go down the line pulling the spark to ground to
run a cyl balance. I would assume as previously mentioned this may be due to
carbon in the make-up of the rubber compound.
"Robert Hancock" <hanc...@nospamshaw.ca> wrote in message
news:n43%9.173163$sV3.6...@news3.calgary.shaw.ca...
Steve
>
> How can "touching any metal part" of the car DISCHARGE static electricity if
> the TIRES are INSULATING it from the ground ?
>
You need to do that precisely BECAUSE the tires are insulating. YOU
become the conductive path, discharging the static differential voltage
between your body on the car. If you don't, the risk is that the
discharging spark will occur between the gasoline filler neck and the
filler nozzle when you are inserting it into the tank. Note that
"ground" need not even be involved- your feet are also insulated from
ground. The spark occurs just because your body and the car body acquire
a charge differential when you scoot across the seat and get out of the
car, so a spark between the filler nozzle (in your hand) and the car
body (insulated from ground) can still happen.
Steve
> 90% of the people that blow up at gas stations are women.
> Why? Because women put the nozzle in the tank, get back in the car,
> slide their butts around on the seat, accumulate a static
> charge, get back out, reach for the nozzle and Ka-Boom!
> Men usually just stand there by the nozzle.
Oh, the jokes just waiting to be cracked here.... :-)
Actually, I suspect the fact that women's clothing is about 10x more
likely to be made of either synthetics or more static-prone natural
fibers than men's clothing has more to do with it than how they hold the
nozzle (mpppffft!). Men's clothing is typically cotton or wool, which
don't build up quite as much static as rayon, nylon, silk, etc.
Steve
>I would assume as previously mentioned this may be due to
> carbon in the make-up of the rubber compound.
Any rubber made with carbon black (tires are a prime example, plus
radiator hoses, vacuum hoses- pretty much anything made to be UV and
ozone resistant) will conduct static electricity slowly. It still has
such a high bulk resistivity that it is for all intents and purposes an
insulator, but it is a "leaky" insulator rather than a near-perfect
insulator like natural rubber, glass, nylon, etc.
Bob Hetzel
just to equalize the charge. You don't get a shock if you're at the
same electric potential (i.e. voltage relative to ground) as the car.
You yourself do not have to be grounded, nor does the car, for this to
work.
Electricity only flows when there's a difference in charge. If you
ground 2 objects then you don't get any charge between them because
they now have the same charge. That's just a special case which happens
to be easy to duplicate (and therefore handy). You could equally charge
two objects at any voltage and have the same effect. Both might then
want to spark if the charge can flow to a grounding point, but they
wouldn't spark if brought close together.
""pyats\"@texa_s.net"
about the problem. According to PEI, the ratio really is 90% women
to 10% men. Men normally don't get back into the car, women do.
Watch sometime and see. Just two weeks ago here in Texas, 2 women
and one man burned up at the gas pump.
engit
Steve <n...@spam.thanks> wrote in message news:3E3E97DC...@spam.thanks...
>
> > 90% of the people that blow up at gas stations are ...
> > Why? Because ...
> > ..., accumulate a static
> > charge, get back out, reach for the nozzle and Ka-Boom!
>
> Actually, I suspect the fact that women's clothing is about 10x more
> likely to be made of either synthetics or more static-prone natural
> fibers than men's clothing has more to do with it than how they hold the
> nozzle (mpppffft!). Men's clothing is typically cotton or wool, which
> don't build up quite as much static as rayon, nylon, silk, etc.
My 1992 Mazda has a little round plastic "button" next to the door lock
which the owner's manual says should be touched to discharge static. But it
does not say why I would want to discharge my static. Did the author of the
manual have in mind the possibility of blowing myself up when refilling the
fuel? Or are there other reasons?
engit
Steve <n...@spam.thanks> wrote in message news:3E3E9354...@spam.thanks...
Is the nozzle and pump grounded?
engit
Supertimer <super...@aol.com> wrote in message
news:20030201132309...@mb-cf.aol.com...
> con...@aol.commado (Conase) wrote:
>
> >I was giving a presentation on cars the other night when I was asked a
> question
> >to which I did NOT have an answer and about which I had often wondered .
> >
> >If you are in a LIGHTNING storm or near a DOWNED POWERLINE while in your
car,
> >it is always said to STAY IN the car and avoid touching anything metal.
The
> car
> >is supposed to "insulate/protect" you from the electricity.
> >
> >We had a backhoe operator at my school who was saved by the RUBBER WHEELS
when
> >the blade hit 2-3 inch feeder cables NOT on the plans from 1903. The
> >electricity MELTED the substantial steel finger off the blade.
>
> Insulate is not the right word. Conduct is. Electricity always finds
> the easiest path to ground. When lightning hits your car, the
> electricity is conducted around the metal body of the car to the
> ground because it is an easier path than through air or through
> you. The rubber in the tires do little to stop the electricity of that
> high a voltage. Even if it did, the electricity will have no problem
> jumping from the lowest metal point in the car through the air to
> the ground.
What if there car is moving. Can lightening heat up the tire and rupture it
(causing you to lose control)? If so how likely is it?
Ad absurdum per aspera
> it is always said to STAY IN the car and avoid touching anything metal. The car
> is supposed to "insulate/protect" you from the electricity.
Lightning and downed power lines are somewhat different situations.
When you're under a downed power line (or, more likely, suspect that
you might be but have no safe way of making sure), the insulating
effect of the tires is significant. (At least for powerlines of the
ordinary sort, not the main lines that take huge voltages cross
country.) And the metal in the body and chassis gives any electricity
that might be flowing someplace better to go than through you -- you
don't want to subvert that benefit by touching something electrified
and either giving it a significant secondary path to ground (it
divides in proportion to conductivity rather than being all or
nothing).
With lightning or the aforementioned really big power lines, with
colossal voltages, I can't imagine that the inches of insulation
between the car and ground, or between metal and your body matter much
-- the safety cage effect is what you've still got going for you, and
indeed you seldom if ever hear of a driver being killed as a direct
effect of lightning.
Another key difference of course is that when lighting is over, it's
over, whereas a downed power line could, unbeknownst to you, remain
energized.
> We had a backhoe operator at my school who was saved by the RUBBER WHEELS when
> the blade hit 2-3 inch feeder cables NOT on the plans from 1903. The
> electricity MELTED the substantial steel finger off the blade.
I'd guess that he was saved by the metal structure of the blade and
equipment. Plainly the electricity *did* go to ground -- it just had
a much better route than through him. (He's still lucky -- and even
luckier that he didn't hit a gas main. Dangerous things that aren't
on the plats are the curse of the heavy equipment operator.)
> How can "touching any metal part" of the car DISCHARGE static electricity if
> the TIRES are INSULATING it from the ground?
Here's yet still another different situation! In this case the
passenger generates the static -- it's like little lightning, and
you're the cloud! the current is small enough that the car body
constitutes a ground. The tires and thence the actual dirt type
ground aren't in the circuit. A tip: if you use your car keys rather
than your finger you won't get a shock.
Many if not most tires are made to be a bit conductive in order to
reduce nuisance static. However, this is supposed to be regarded as a
convenience feature and not as a means of hazard prevention. It's
also irrelevant if you and the surface your clothes are rubbing
against are off ground (until you grab the door frame and ka-zap!).
Consider also the case of someone filling up gas cans inside a
pickup's bed or a car's trunk. Now, there the grounding comes from
the pump nozzle, not exactly the place where you want to draw a spark
to say the least. Thus the warning signs imploring you to take the
cans out of the vehicle and set them on the pavement.
I think static has gotten to be a worse problem in recent years.
They're making car interiors out of different stuff, and dealers or
owners apply fabric protectants liberally. Also, may pickups now have
plastic bedliners, though even with the regular metal kind you're
supposed to remove gas cans before filling. I don't recall getting
many static shocks from cars made before the early 80s when these
changes started coming about on a large scale. Now I get zapped all
the time.
Cheers,
--Joe
Steve
Not always. Some nozzles are grounded either by a small external wire on
the fuel hose, or by an internal coil in the fuel hose. But many of them
are not grounded.
""pyats\"@texa_s.net"
the problem. The problem is that the nozzle when stuck in a gas
tank is grounded to the vehicle. The vehicle is grounded to the ground
via the tires. Tires may be good for insulating a few volts but
not for insulating against tens of thousands of volts.
""pyats\"@texa_s.net"
due to thunderstorms and tornados. What saves people inside of vehicles
is the Faraday Cage effect. Charges reside on the outside of objects.
If you were sitting on the outside of your car and power lines or
lightning hit it, you would die. That is why construction workers
on tractors and backhoes die.
engit wrote:
>
> What if there car is moving. Can lightening heat up the tire and rupture it
> (causing you to lose control)? If so how likely is it?
Don't worry, lightning rarely hits moving cars.
Michael Knight
> Tires are not very good insulators... especially when they are wet
> due to thunderstorms and tornados. What saves people inside of vehicles
> is the Faraday Cage effect. Charges reside on the outside of objects.
> If you were sitting on the outside of your car and power lines or
> lightning hit it, you would die. That is why construction workers
> on tractors and backhoes die.
>
I was thinking the car body acted as a Gaussian shell....or is that
the same thing as a Faraday Cage? Been a while since I had E-mag back
in college.
But I've read about tractors and combines hitting high voltage power
lines before and the people are fine....as long as they stay in the
cab. Seems a couple of the stories I read, the drivers got panicky
and jumped, only to die when they hit the ground. In fact, the more
gruesome tale I remember was some wheat combine that hit above ground
lines. The woman driver jumped despite her neighbor running and
yelling for her to stay put.
The neighbor said she landed a good 10 feet from the tractor, but the
electricity actually arced and pulled her back against the frame and
held her there. I think the neighbor tried several attempts to pull
her off, and himself absorbed so much voltage that it actually welded
several of his fingers together .
Nasty!
""pyats\"@t_exas.net"
it sure sounds similar.
Interesting discussion.
ray
> ""pyats\"@texa s.net" wrote in message news:<rN6cnQ5fwaX...@texas.net>...
>
>>Tires are not very good insulators... especially when they are wet
>>due to thunderstorms and tornados. What saves people inside of vehicles
>>is the Faraday Cage effect. Charges reside on the outside of objects.
>>If you were sitting on the outside of your car and power lines or
>>lightning hit it, you would die. That is why construction workers
>>on tractors and backhoes die.
I'm still not convinced that it has anything to do with the car
being a Faraday Cage. I believe it's simpler than that - if the
car body is energized with a high voltage line, as long as you
don't complete the circuit to ground, you'll be fine. In fact,
if you had a voltmeter and connected it across the sheetmetal,
it would still read 0 Volts. There's no potential difference
across the sheetmetal, so as long as you keep the door shut
you're ok. It's when you are touching the car AND the ground
that you're toast - you become a conductor.
That and a car makes a lousy Faraday cage with all the holes
in it for windows ...
Ed Price
"Michael Knight" <rep...@phantom.homelinux.net> wrote in message
news:90e332cb.03020...@posting.google.com...
> ""pyats\"@texa s.net" wrote in message
news:<rN6cnQ5fwaX...@texas.net>...
> > Tires are not very good insulators... especially when they are wet
> > due to thunderstorms and tornados. What saves people inside of vehicles
> > is the Faraday Cage effect. Charges reside on the outside of objects.
> > If you were sitting on the outside of your car and power lines or
> > lightning hit it, you would die. That is why construction workers
> > on tractors and backhoes die.
> >
>
> I was thinking the car body acted as a Gaussian shell....or is that
> the same thing as a Faraday Cage? Been a while since I had E-mag back
> in college.
That's OK; don't let lack of knowledge hinder from giving advice.
Ed
richard schumacher
Conase wrote:
> How can "touching any metal part" of the car DISCHARGE static electricity if
> the TIRES are INSULATING it from the ground ?
It wouldn't if the tires were insulators, but they're not: auto tires have some
graphite in them to make them a little conductive. This is so the car won't
accumulate a static charge.