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boris_73

The Official "Quick Question" Thread

273 posts in this topic

I know there's a ''š'' over the word. We speak the same language.

 

Hmm, it's really strange. I googled the term ''vertex'' and it really isn't the same as ''hvatište''. There is only one website that attempts to translate the word, and it is into: ''point of application of a force''. That doesn't sound right. Doesn't sound like a term.

 

 

Whenever a language is translated any shortage of relative experience will lead to a lack of understanding to one degree or another the more it's translated, down the line, the less understanding there is.

 

In view of this, I can see how that term is an approximation of a meaning full sentence.

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What actually do we know about lightning? As far as I've read, the process whole process of cloud-to-ground lightning is not well understood and therefore, not proven.

What parts of knowledge about lightning do we know for certain and which are unclear?

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What actually do we know about lightning? As far as I've read, the process whole process of cloud-to-ground lightning is not well understood and therefore, not proven.

What parts of knowledge about lightning do we know for certain and which are unclear?

 

Clouds charge, the charge separates and you get a discharge when the potential difference is big enough.

 

We can measure the discharge locations, current flows etc... What do you want to know? I'm not an expert but I know a bit.

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I want to know about the process of lightning getting from the cloud to the ground. I want to know how and why exactly and if there is proof of the explanation. As far as I know, the ''main'' explanation is not considered as fact, neither is any other (obviously).

 

Here's a quote from Wikipedia:

 

 

In a process not well understood, a channel of ionized air, called a "leader", is initiated from a charged region in the thundercloud. Leaders are electrically conductive channels of partially ionized gas that travel away from a region of dense charge. Negative leaders propagate away from densely charged regions of negative charge, and positive leaders propagate from positively charged regions.

The positively and negatively charged leaders proceed in opposite directions, positive upwards within the cloud and negative towards the earth. Both ionic channels proceed, in their respective directions, in a number of successive spurts. Each leader "pools" ions at the leading tips, shooting out one or more new leaders, momentarily pooling again to concentrate charged ions, then shooting out another leader.

 

I have heard of this explanation and similar ones. Generally speaking, everyone knows that cloud particles get brushed together and thus, charged, and there is discharge from the cloud to the oppositely charged ground. Typically, the lightning flows from the negatively charged base of the cloud to the positively charged ground. But how the charge actually travels from the cloud to the ground is unclear to me.

 

I want to know if this explanation is considered to be proven science and why so. As far as I know, it isn't.

Edited by Lord Antares
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If I knew the answer, I'd have given a better reply. See Wikipedia: https://en.wikipedia.org/wiki/Lightning

Sorry, I'm on my phone and it could be quite a big subject depending on what he wants to know. The NOAA document referenced in the wp article is a good place to start.

I want to know about the process of lightning getting from the cloud to the ground. I want to know how and why exactly and if there is proof of the explanation.

This is quite easy and distinct from what you go on to ask. The lightning getting from the cloud to the ground is just a flow of charged particles when the breakdown voltage is exceeded. That causes a broadband em discharge and heating around the channel. Normally you get an upspike from the ground first then a down spike. This is well observed.

 

How the charge builds up is a different question. The NOAA explanation is the one commonly accepted in the literature. But it's not really my area.

Lightning mapping arrays are pretty cool e.g. http://ibis.nmt.edu/nmt_lms/

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.Normally you get an upspike from the ground first then a down spike. This is well observed.

 

No, it's the opposite

 

8qV7l.gif

 

 

This is quite easy and distinct from what you go on to ask. The lightning getting from the cloud to the ground is just a flow of charged particles when the breakdown voltage is exceeded. That causes a broadband em discharge and heating around the channel.

 

Well, no. Here's another quote from Wikipedia:

 

 

 

Initiation of the outward leaders is not well understood. The electric field strength within the thundercloud is not typically large enough to initiate this process by itself.[22] Many hypotheses have been proposed. One theory postulates that showers of relativistic electrons are created by cosmic rays and are then accelerated to higher velocities via a process called runaway breakdown. As these relativistic electrons collide and ionize neutral air molecules, they initiate leader formation. Another theory invokes locally enhanced electric fields being formed near elongated water droplets or ice crystals.[23] Percolation theory, especially for the case of biased percolation,[24] [clarification needed] describes random connectivity phenomena, which produce an evolution of connected structures similar to that of lightning strikes.

 

Do you see what I mean now? There is no wire that connects the cloud and ground. It isn't know how exactly this travels towards the ground and in what way. I hope that clarifies what I mean to ask.

Edited by Lord Antares
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Ah I see what you're asking. How the charge flows the way it flows? Other than in a straight line just as a flow of charge which you might expect from a breakdown? And why the breakdown occurs when it occurs?

 

Then we don't really know. The atmosphere is a complicated system that is pretty difficult to do subtle experiments on. There are loads of quite small scale effects that just go completely unmeasured at the moment. With much cheaper easier to deploy in situe measurements that will hopefully become available in the next 5 years this will change.

 

I'm sure the talk I was at last week showed upspike first in about 80% of cases. Sleep time now. I'll try and find a reference tomorrow. But it's not my area so I may have misremembered.

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Yes, that's exactly what I'm asking. Yeah, that's what I thought.

 

Hm, the Wikipea article states that the downward one comes first. All the other GIFs show it that way too. It would make more sense as well, as the cloud is the supercharged body, so it would make more sense that the discharge is initiated by it, right?

 

You either misheard, misremembered, they mis-explained or I stumbled onto an unlucky string of coincidentally wrong explanations.

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In a thunderstorm, is the sky between the clouds and the ground negatively charged or NET negatively charged?

 

What is the maximum distance of attraction between a proton and an electron?

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The proposed SpaceX Earth-Mars Luxury Liner has a top stage of 17m diameter with a booster stage of 12m diameter. What is the benefit of having a 12m dia booster? I believe material and weight could be saved by having the booster 17m dia.

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Yes, that's exactly what I'm asking. Yeah, that's what I thought.

 

Hm, the Wikipea article states that the downward one comes first. All the other GIFs show it that way too. It would make more sense as well, as the cloud is the supercharged body, so it would make more sense that the discharge is initiated by it, right?

 

You either misheard, misremembered, they mis-explained or I stumbled onto an unlucky string of coincidentally wrong explanations.

A couple of months ago I saw an inverted stroke of lightning ie. forked upwards rather than down. I assume that in this case the leader propagated from the ground upwards & the actual strike was downwards.

(Apparently this is caused by metal masts and towers which concentrate the Earth's charge at a single point.)

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I THINK (not 100% sure) that we almost always see the upward stroke, even though both the downward one and the upward one happen.

So it might have been a normal lightning and you saw the upward one pronounced. I would have to go back to research that as I'm speaking from memory.

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I THINK (not 100% sure) that we almost always see the upward stroke, even though both the downward one and the upward one happen.

So it might have been a normal lightning and you saw the upward one pronounced. I would have to go back to research that as I'm speaking from memory.

 

A quick search for "ground to cloud lightning" shows that the phenomenon is more common than I would have thought. And that, yes, this gives lightning that forks upward.

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I know, but we have cloud-to-ground and ground-to-cloud in both types of lightning. I think both need to be there.

So you may have witnessed ground-to-cloud lightning or the return stroke of the regular cloud-to-ground lightning.

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I think you will find that the stepped leader causes the forked shape of the lightning. Therefore, in an inverted forked bolt, the leader must be propagating upwards rather than downwards as in a normal strike. Presumably the main discharge is also in the opposite direction to that of a cloud to ground discharge.

 

(When I took my (French) pilot exam, there was only one question related to thunderstorms. The question was 'What is this?' with a picture of a Cumulo-Nimbus. The correct answer was 'Dangerous'.)

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There are now estimates of how many Earth like planets exist in the Milky Way. Do we know enough about the history of our galaxy to estimate how many of those worlds have been sterilized by stellar explosions, whether such worlds may recover enough to support life after sterilization, and how such events affect our expectation of finding aliens.

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I have a quick question. One that I really should know the answer to. And am almost embarrassed to ask. But I was watching a documentary on the history of our space program the other night, and this question came to me. I could look it up but this is more fun.

 

So....here goes.....Gravity. as in....The Earth's. Does our planet's gravitational field lessen as one rises in altitude toward the boundary of space? Or is it uniform all the way up? Until we escape it totally and enter the weightlessness of Space. Which, if memory serves, is agreed upon you be about 60 Miles up?

 

So....Yeah, do you weigh less up at, say, thirty miles than you do at one mile? Or is it all uniform and equally spread? Like going through a jar of honey till you break the surface?

 

Thanks.

Edited by Velocity_Boy
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No, it is always dependent on the distance from the object, hence the inverse square law. So, the higher you are, the lesser the effect of gravitation on you. There's even a greater effect at sea level than, say, on a mountain.

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No, it is always dependent on the distance from the object, hence the inverse square law. So, the higher you are, the lesser the effect of gravitation on you. There's even a greater effect at sea level than, say, on a mountain.

Really? I never heard about the lesser gravity at altitude? For instance, I used to live in a town that was 7200 ft. Elevation. And while we all knew about the thinner air and it's effects....I'm a runner!...I never heard about less gravity. I'm sure it's negligible though, eh? Like I maybe weigh half of an oz. Less in Flagstaff than in Austin?

 

So, Denver. The Rockies baseball team. Their stadium Coors Field. Renowned for balls going farther, more home runs, a pitcher's nightmare. I always attributed all that to thinner air. Do you mean to say lesser gravitational pull is also part of the equation? How can I never have heard this? LOL

Edited by Velocity_Boy
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No, the effects are much too negligible. I really don't know how you've never heard of it, it has been well known for a few hundred years that gravity falls off with distance.

See Newton's inverse-square law: https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation

 

How else would gravity work if it didn't fall off with distance? Everything would be one body in the universe.

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