how fast does lightning travel

how fast does the end of the lightning bolt travel?

I don't know, but is there anyone who can confirm that lightning begins from the ground and why?

It's really, really fast.

OK, our old friend EB says that a cloud-to-ground bolt is made up of two strokes: a leader stroke and a return stroke. A leader stroke, which carries a negatively charged from the cloud to ground (except if the structure about to be hit is rather high). The leader stroke begins inducing a positive charge on the ground. The return stroke, carrying the positive charge, moves its way up to meet the leader. They meet at about 50m above ground, short-circuiting the cloud to the ground causing "a highly luminous return stroke of high current (to pass) through the channel to the cloud. "

Now, as for speed:

The entire process is very rapid; the leader stroke reaches the juncture point or the ground in about 20 milliseconds, and the return stroke reaches the cloud in about 70 microseconds.

So speed = height of cloud / 90 ms. Your mileage may vary.

What's this? Are you adding microseconds to milliseconds without a 3-decimal shift? Show your work. Almost no lightening where I live, and I don't think any ever conducts to the ground here, but I wanna know how fast I gotta move if it does. ;-)

Ray (electrical engineer ignorant of the subject)

Oops. I'm mixing my units. And anyway the actual bolt apparently occurs in the 70 microseconds.

Now for my patented Wild Ass Math... The height of a cumulonimbus cloud does not exceed 2km. So 2km in 70us = 30 million m/s. Or about 0.1c. That sound right?

Damn, I was hoping I'd be the first to notice. Plus I get busted by a guy with a metric prefix. How a propo. "Show your work" sends chills up my spine...

Alpha is that for greased or plain ol' unlubricated?

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Signitorily yours, Mr John
" Pardon me while I have a strange interlude."-Marx
ARROW? Officer, I didn't even see any Indians

Nanobyte,

Suffice it to say - you can't run that fast. However, take it from me - a guy who was nearly struck by lightning in a parking lot once - there is an advanced warning signal.

Here's my story. I was camping once when I was about 16 years old and had decided to take a walk around the lake where we were staying. Near the end of the walk, it started to rain heavily. I decided to take a short-cut across a parking lot to get back to my camp site. About halfway across the parking lot I noticed that, in spite of the fact that I was soaking wet, all the hairs on my arm started to stand on end... Instinctively, I fell flat to the ground and lightning struck a small tree about 20 yards away in a landscape island. The first thing I noticed was being covered in toothpicks... the tree almost vaporized... The next thing I noticed was the ringing in my ears and the realization that I could no longer hear the rain or the thunderclap of that last flash of lightning. My hearing finally returned about an hour later, but the ringing persisted for a few days.

I've heard from other near misses that they too noticed a strong electrostatic field just before the strike. I figure I had about 2 seconds of reaction time, but of course time seems to move at a different rate in those situations, so who knows...

How fast? C

(i.e., the speed of light)

I don't know how much I believe it, but I was told in school that electricity moves at almost the speed of light which would be 186,000 mps. I was also told that when enough current has built up to overcome the resistance of the air seperating the Earth and the clouds, that it would still move at near the speed of light.

Do I need to go kick my old science teacher's ass or is this right?

(I know I owe my spelling techer an ass woopin' so don't comment if I misspell anything.)

[JoeyBlades]

dkgreath,

You wrote:


I don't know how much I believe it, but I was told in school that electricity moves at almost the speed of light which would be 186,000 mps.


No. Actually the 'flow' electric current is quite slow - on the order of inches per minute in a wire, but probably not too radically different in air.

The things that do move fast in a lightning strike are (1) LIGHT, which travels at basically... the speed of light [though remember we're not dealing with a vacuum, here] and (2) ENERGY. To understand how the energy is transferred at incredible speeds, consider this analogy.

Imagine I have a one mile long, very hard, very rigid rod. I place one end of this rod about 1/8th inch from a bell and stand at the other end of the rod. Now I strike this end of the rod with a hammer - ignoring friction and compression effects on the rod, the energy is transfered almost instantaneously to the other end of the rod and rings the bell.

This is very similar to the way electricity works, except the rod is replaced by electrons in whatever conductive medium you're dealing with - in this case, charged air.

You're best to not conceptualize electricity as moving, but rather pushing.

[Nickrz]

This from NASA's lightning research web site:
(Well worth the visit just for the lightning primer).

http://thunder.msfc.nasa.gov/

With the initial breakdown of the air in a region of strong electric fields, a streamer may begin to propagate downward toward the Earth. It moves in discrete steps of about 50 meters each and is called a stepped leader. As it grows, it creates an ionized path depositing charge along the channel, and as the stepped leader nears the Earth, a large potential difference is generated between the end of the leader and the Earth. Typically, a streamer is launched from the Earth and intercepts the descending stepped leader just before it reaches the ground. Once a connecting path is achieved, a return stroke flies up the already ionized path at close to the speed of light. This return stroke releases tremendous energy, bright light and thunder. Occasionally, where a thunderstorm grows over a tall Earth grounded object, such as a radio antenna, an upward leader may propagate from the object toward the cloud. This "ground-to-cloud" flash generally transfers a net positive charge to Earth and is characterized by upward pointing branches.

[NanoByte]

Greath:

I'll overlook the spelling, but. . .uh. . .in an electrostatic situation, it is not "current" that "build[s] up", but rather electric potential (voltage).

Blades:

The things that do move fast in a lightning strike are (1) LIGHT, which travels
at basically... the speed of light [though remember we're not dealing with a
vacuum, here] and (2) ENERGY.

You don't consider light to be energy? And some of the energy is in the form of sound (thunder), which travels at only 738 mph at sea level.

Imagine I have a one mile long, very hard, very rigid rod. I place one end of this
rod about 1/8th inch from a bell and stand at the other end of the rod. Now I
strike this end of the rod with a hammer - ignoring friction and compression
effects on the rod, the energy is transfered almost instantaneously to the other
end of the rod and rings the bell.

What can I do with this, unless you calibrate "almost instantaneously"?

You're best to not conceptualize electricity as moving, but rather pushing.

Well, when push comes to shove. . .

"Electricity" (I didn't think we used that term anymore, actually.) pushing is 'potential'/'voltage'.

"Electricity" moving is 'current'/'amperage'.

Now, about electricity pulling. . .

Which leg would you like it on?

Ray (If that charged you too much, just coulomb down a little.)

[JoeyBlades]

Nano,

You wrote:


You don't consider light to be energy?


Yeah, you caught me oversimplifying again... I should know better, with you around. I was trying to differentiate between the fairly benign light energy and the fairly destructive EMF (Electro Motive Force)...


What can I do with this, unless you calibrate "almost instantaneously"?


Damn. I though I could slip that one quietly through the net, too... The energy moves at different rates through different media and is dependent on a number of different factors like friction, compression, etc..If the material were perfectly elastic and rigid, and there were no other mitigating factors such as friction, then the energy would be transmitted exactly simultaneously (i.e. faster than the speed of light). In the real world, I'm sure it's significantly slower...

Trying to bring this back around to the topic... Nickrz wrote:


Once a connecting path is achieved, a return stroke flies up the already ionized path at close to the speed of light.


Again, this "return stroke" is referring to the EMF, not the voltage or current. I'm not sure how they arrive at that "close to the speed of light" business, but I think it's a bit deceptive. It makes people think that the velocity of this energy is somehow related to the speed of light and constrained by the same limits, but this is not the case. I think they probably use "the speed of light" because most people can conceptualize this as something that seems instantaneous, but intellectually they know it's not...

[falcon2]

then the energy would be transmitted exactly simultaneously...It makes people think that the velocity of this energy is somehow related to the speed of light and constrained by the same limits, but this is not the case.

I have never heard of a single energy vector that propagates faster than light, and every "exactly instantaneous" phenomina I have every heard of is a misapplication of classical mechanics on the quantum level. Maybe you could enligten us with a few examples?


this "return stroke" is referring to the EMF, not the voltage or current.


EMF stands for electro magnetic frequency which is a very broad description of "light" from power waves through cosmic rays. And the EMF from the lighinging is a side effect of the moving charge, and the recombination of electrons and ions, and is not a seperate phenomenon. The channel ionization happens in the initial stroke with the stepped leaders and streamers. Most of the current discharge and heat generatrion happens in the return strokes.


I think they probably use "the speed of light"

I have heard discovery channel say 4,700m/s is "nearly the speed of light." The speed of light in a vaccuum is 299,792,458m/s. Its not possible for the E field change to propagate faster than this, or FTL communication would have been commonplace years ago.

[falcon2]

EMF stands for electro magnetic frequency

Doh.
EMF stands for electro magnetic field.
So, I'm an idiot.

[JoeyBlades]

Falcon wrote:


EMF stands for electro magnetic field.


I think Electro Magnetic Field must be the more modern use of this TLA, however I have several text books from my Electrical Engineering studies that refer to EMF as Electro Motive Force.



I have never heard of a single energy vector that propagates faster than light, and every "exactly instantaneous" phenomina I have every heard of is a misapplication of classical mechanics on the quantum level. Maybe you could enligten us with a few examples?


You were not listening. I said that a perfectly elastic, perfectly rigid material in an environment without friction could transmit energy faster than the speed of light. No such material or medium exists... You don't even have to go to the quantum level before the analogy breaks down in the real world.

[falcon2]

I think Electro Magnetic Field must be the more modern use of this TLA, however I have several text books from my Electrical Engineering studies that refer to EMF as Electro Motive Force

Actually electro-magnetic field is OSHA mumbo jumbo, I was obviously thinking you meant EMR when I wrote my response.


this "return stroke" is referring to the EMF, not the voltage or current.

The common units on EMF are umm...VOLTS

I said that a perfectly elastic, perfectly rigid material in an environment without friction could transmit energy faster than the speed of light. No such material or medium exists...

How bout an example? If you have some idea on moving energy FTL, we all want to hear it.

[gary horaczek]

How fast does lightning travel? It depends if there is a cop around with radar.

[Pete]

JoeyBlades, how can, in theory, something be elastic AND rigid?

[Nickrz]

The head of a hammer is one example.
Not theory, fact.

[mr john]

My head is a theory,and thats a hard fact.
Nick is right though.
I was struck by lightening in my right big toe when I was 10 or 11.True

[JoeyBlades]

Pete,

Elastic (in physics) means "no loss of kinetic energy between particles during a collision" - or something close to that, I don't have my physics dictionary handy for an exact quote.

It has virtually nothing to do with that rubber-bandy material that makes up the wasteband of your boxers...

[bbeaty]

Check out this mental exploration of lightning:
WHAT IF LIGHTNING TRAVELLED SLOWLY? http://www.amasci.com/tesla/spark.html

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BILL BEATY billb@eskimo.com
http://www.amasci.com SCIENCE HOBBYIST
Seattle, WA USA

[bbeaty]

Here's a subtle aspect of the speed of lightning "leaders". A leader does not travel at the speed of light, nor does it travel at the speed of the moving charges. What then creates its speed? Something weird! A lightning leader is a conductor. It is a HIGHLY CHARGED conductor.
What happens when a long, thin conductor has an immense charge on it? It grows "St. Elmo's Fire" at any sharp spots, therefor the tip of an advancing lightning leader will "shatter" the air into plasma (into separated electrons and positively-ionized nitrogen molecules).
But the leader itself is made of plasma. Right. In other words, the charge on the plasma-filament makes the plasma-filament grow longer.

What controls its speed? All kinds of things. The speed of leader growth is obviously limited to the speed of light, but the LOWER limit on the speed of a leader is millions of times slower.
I've seen lightning leaders crawl slowly across the base of a thunderstorm, maybe going a couple of miles per second. I've seen videotapes (http://www.tornadoproject.com) where the same sort of horizontal lightning appeared to crawl at a fraction of a mile per second.

The speed of a lightning-leader is mostly controlled by the gradient of voltage at its tip. If a leader is highly charged, it will go faster. If a leader invades a cloud which contains opposite charge, then the leader will become highly charged by "induction", and therefor will go faster.
If a leader wanders out away from the charged clouds, it can slow down and stop entirely (we've all seen branched lightning, no? Where many branches just hang out in space with nothing at their tips?)

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BILL BEATY billb@eskimo.com
http://www.amasci.com SCIENCE HOBBYIST
Seattle, WA USA

[JimFox]

We don't have many lightning storms in SF and hwne they we do they are strange. Sometime thunder will rumble for almost a mniute. I've lived here 25 years and have been in maybe 5 at most, all very mil. During one I was watching, shooting out from the street in front of my house, at about a 45 degree angle were what appeared to be bottle rockets. They traveled at about the speed of a bottle rocket and must have been some sort of lightning.

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www.cyberthings.com (http://www.cyberthings.com)

[pluto]

IIRC, the speed of the electric current in a good conductor, like copper wire, is about .3c, so the earlier estimate of .1c for lightning's return stroke seems about right.



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"non sunt multiplicanda entia praeter necessitatem"

[mr john]

St Elmos fire is really weird I have only seen it a few times.Once along a barbed wire fence,the wires had an 'aura' along them that slowly concentrated around the barbs then to the tops of the metal fence stakes. Jim, the stuff you saw has a name but i forget what it is, I have seen that out on the plains too.That was a great discription of it. It seems to be intermediary between St.Elmo's and 'real' lightening. ( ball lightening may or may not exist I have never seen it but..).Those long low rumbles are from horizontal lightening aWWWAY up there.It can travel dozens of miles,instead of the thousands of feet vertical stuff does. When it is lower you can hear it coming, it's real nice when it's directly over head, that low rumble getting louder , beginning of a boom,then the a great loud sharp KeeeeeeRACK! that makes windows rattle,old ladies pee their pants and cattle stampede, then it rumbles away . Actually you don't hear it coming, by the time you hear it, it's done left here and gone.Cause lightening is real fast. i don't know how fast, I think I will start a topic on that when i leave here.

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"Pardon me while I have a strange interlude."-Marx