Car getting struck by lightning

[davenn]

Hmmmm a fine line of definition maybe ;)
I was working on the principle that no current flows without a completed circuit
which doesn't happen till the leader/streamer from the ground meets the stepped leader from the cloud

I see where you are coming from and by definition it could be called a current
as a current is the flow of charge
( I'm sitting here and ummming and harring ;) )

I see it as an area of charge propagating out ...
how about an expanding electric field :)

I'm open to a clearer definition if one can be found :)

have a look at this classic pic, and this is for DTM as well

note the 2 streamers/leaders from the ground, one from the power pole yellow arrow)
and the one from the tree. Amazingly there must have been another leader from the tree that reached further and initiated the discharge

Dave

 

[DTM]

That's all fine and dandy, but you need to be able to support your opinion with references.

So if Einstein had wanted to discuss his theory of relativity on this forum, he shouldn't be able to because he'd have had no references ;) I know your response will be DTM is no Einstein...
I think all of this discussion is still relevant to the original topic which is basically, does an insulator effect an object being struck by lightning... I'm learning a lot from this discussion anyway.

Dave, The car getting struck by lightning does not disprove my point about relative resistance. You'd have to have 2 cars next to each other, one on rubber tires and one on steel rims and show they both get struck equally often...

So if a streamer does have some current, an insulator should affect that current and may affect which object 1st initiates that streamer.
I'm still uncertain. If it's true that an insulator has no effect on where lightning will strike, do you really expect a lightning rod to work as well if you attach it to a rubber boot sitting on the ground vs a metal rod driven into the ground?
However, I like Dave's example of static discharge from a carpet, which does seem to work just fine with rubber shoes... Too late to think about this anymore tonight.

 

[Drakkith]

So if Einstein had wanted to discuss his theory of relativity on this forum, he shouldn't be able to because he'd have had no references ;) I know your response will be DTM is no Einstein...

If this forum existed prior to Einstein's publications on relativity, no, he wouldn't be able to discuss them. Afterwards, yes, and he could simply "link" the peer reviewed papers as references.

So if a streamer does have some current, an insulator should affect that current and may affect which object 1st initiates that streamer.

Not necessarily. This isn't a wire and a resistor. An large insulator may have a much lower amount resistance than you'd think when it comes to high voltages just because of its size, similar to how increasing the cross sectional radius of a conductor decreases its resistance.

I'm still uncertain. If it's true that an insulator has no effect on where lightning will strike, do you really expect a lightning rod to work as well if you attach it to a rubber boot sitting on the ground vs a metal rod driven into the ground?

No, but lightning rods aren't built to simply attract the lightning, but to discharge it to ground without itself or the structure it's mounted on being destroyed in the process. This could be the main reason that lightning rods are connected to low impedance systems designed to transfer very high current to ground and may have little to nothing to do with the buildup of charge and the initiation of an upward streamer. And for the record I am not saying that the resistance of an object doesn't matter, I'm questioning your claim that it matters enough to greatly affect where a lightning strike will occur, especially in the context of two objects several dozen feet from each other.

 

[zoki85]

Few comments:

• In the case of an indirect strike it is certainly better to wear footwear with good insulating soles than standing barefoot. However, if step voltages are sufficiently high, footwear is useless: arcover will occur at voltages in order of few kV and the footwear insulation/resistance will be bypassed this way.
• I don't know of any studies/research conducted in HV labs showing difference in probability of direct strikes between set-ups with good grounding, bad grounding and thin piece of insulation put between base of the object and ground. IMHO, the difference should exist but is likely to be too small in megavolt experiments and objects of decent size.
• Streamers, or better long streamer-leader plasma structures, do carry significant impulse currents, have high peak dissipation power, and do change E-field configuration in space significantly (see my avat)
• Many things about lightning are still wrapped in mystery for modern science. Certain features of natural lightning discharge can be reproduced by UHV impulse generators in multimeter gaps; some others can not. Best what can be done is to study a rocket-initiated lightning during thunderstorm weather (there are few facilities in world than can do that). In such experiments an upward positive leader is generated. However, natural cloud to ground lightning is created by downward negative leader in aproximately 90% of the cases

 

[FactChecker]

I will say it one more time
With a static charge and its buildup, materials electrically resistant to DC are IRRELEVENT to the flow of a current resulting from a static charge buildup

The streamers are NOT carrying current ... there is NO current flow till the discharge occurrs

The question is not what happens after a static charge buildup. The question is whether you share the static charge buildup in the Earth that attracts lightning or causes streamers. Shoes can keep a static charge buildup in the Earth from traveling to you.

 

[zoki85]

Shoes can keep a static charge buildup in the Earth from traveling to you.

When downward leader at potential of aproximately -50 MV fast approaches to you, the charge buildup can be hardly called static.

 

[davenn]

Shoes can keep a static charge buildup in the Earth from traveling to you.

not likely ... for the reasons I have already stated ... reread the shoes on carpet then discharging on the door knob

 

[NascentOxygen]

Whenever there's a report of someone being struck by lightning, if there's one further detail I seem to learn it's that the person's shoes were blown off by the strike! It appears that shoes are no impediment to a lightning bolt---it deftly removes them!

What is amazing is that people survive a strike as often as they do, going on to gradually recover almost all affected faculties.

http://thumbnails109.imagebam.com/37332/0363e9373319108.jpg

 

[zoki85]

Person's shoes get frequently blown off in other HV incidents above 20 kV too. Unfortunatelly, people who survive, rarely recover completely.