Bryan,
One of the things about static electricity is you do encounter
exceptions to the rule, but here goes at least a generality: they put
carbon in rubber to make it black, and tires become static dissipative.
If you went and put the leads of an ohmmeter against a tire you'd say
it's an insulator, non-conductive and should charge up just like Keith's
seat cushion. But, when we talk about static, what we're talking about
is voltage, big, crazy electrical pressure. When KT grounds out, he's
discharging on the order of 4KV to just feel it, and when you really go
bang turning on the TV after shuffling across the carpet in your
slippers, probably 10 or 15KV. So when we measure somethings ability to
pass static charge, we need a different range of values and test
methodology, typically using a high voltage ohmmeter, a "megger". If you
so tested a tire, I think you'd find it'd be around 10 to the 6th or 8th
power in ohms, and that would pass static, discharging a big capacitor
like Keith comparatively slowly but well under a second, without any
sensation. Surfaces in electronic handling areas these days have static
dissapative characteristics which is good; they get rid of static but
don't provide a hard grounding path that could hurt somebody. So, tires
don't charge up, rather dissipate any static there might be through the
vehicle.
Anecdotely, one of my static buddies used his knowledge gainfully
when buying a boat. Boat surveyors use meggers to ascertain whether or
not the balsa or foam core of a fiberglass boat has absorbed water. The
fix is pricey, routing out the exterior 'glass and core as far as
necessary, then replacing same. My pal looked at a big boat that had a
bad review as to the status of the core. He checked out the hull with
his megger and found poor but variable readings throughout Suspicious,
he bummed a sander and sanded through the bottom paint to find a coat of
black bottom paint. Sanding through that, he found the hull quite
insular! What to do? Who has any idea what the hell he'd be talking
about? Would the owner sue the surveyor for incompetence? A lawyer
party? My buddy bought the thing....
In closing, years ago, I got a bunch of phone calls from the
Massachusetts Turnpike folks, where a newly resurfaced and upgraded toll
plaza was staffed by collecters that were getting absolutely hammered
with static shocks from drivers handing them money (where are you, Allen
Funt). They were using gloves and plastic cups to collect the tolls,
anything to avoid the torture. All I could propose was some sort of
grounding method (an antenna sticking up to contact the cars from
below?) just before the booth. This of course flies in the face of what
I started out by saying, that tires are dissipative..... I guess we
should all just THANK GOD that we don't get all charged up speed
racing! BJ in Beantown
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