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Thread: Lightning @ NUS

  1. #61

    Default Re: Lightning @ NUS

    read your posts...you are basically saying standing on one leg will keep you alive because of potential differences...draw your picture with a bolt hittng your stick man, and your stickman standing on one foot on the ground.


    and if you are not talking direct strikes, and this is your arguement, then standing on one foot or two makes no difference if the bolt has already hit ground. electricity has already found it's path to ground with least resistence.

  2. #62

    Default Re: Lightning @ NUS

    But... A person's foot is not a point... From the toes to the heel, that's xcm of distance... xcm on the ground meant great potential difference ya? So will I still get kill?

    Best solution... When lighting strikes, jump! (just joking of course!)
    I am NOT a PROfessional photographer and photography is NOT my hobby

  3. #63

    Default Re: Lightning @ NUS

    Quote Originally Posted by Youhong View Post
    But... A person's foot is not a point... From the toes to the heel, that's xcm of distance... xcm on the ground meant great potential difference ya? So will I still get kill?

    Best solution... When lighting strikes, jump! (just joking of course!)
    OMG!!!! THANKS FOR GETTING THE RIGHT IDEA!!!!

    phew....but regarding about the same foot hacing a potential gradient, the thing is that directly underneath the foot itself, the potential is also dropping with the increase in x with the foot. then again, having a current through a foot is definatly less deadly as compared to the whole lower body.

  4. #64

    Default Re: Lightning @ NUS

    Quote Originally Posted by Hawaiisg View Post
    and if you are not talking direct strikes, and this is your arguement, then standing on one foot or two makes no difference if the bolt has already hit ground. electricity has already found it's path to ground with least resistence.
    wrong. go read up on how ground strikes kills many cows with just one strike.

  5. #65

    Default Re: Lightning @ NUS

    Quote Originally Posted by Hawaiisg View Post
    read your posts...you are basically saying standing on one leg will keep you alive because of potential differences...draw your picture with a bolt hittng your stick man, and your stickman standing on one foot on the ground.
    yes...... of course that will kill despite one or two legs. but that's direct hit.

    you see, this argument started because our dear CSer experienced a ground strike. if he experienced a direct hit, he wun even be here now.

  6. #66

    Default Re: Lightning @ NUS

    Quote Originally Posted by satay16 View Post
    okokok...calm down.............calm............calm............ let me explain my case dear 20 years experience high voltage cable guy.

    this is my case for a ground strike, repeat, ground strike

    ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike ground strike

    ok. that should be enough.



    when your feet are equidistant away from the point of strike, they are standing on the same equipotential line. eg, position A. since there isn't any voltage gradient, no current flows through the legs, meaning, no harm.

    but if the feet and point of strike are collinear, it means that the feet are standning in different equipotential lines, creating a voltage gradient. therefore, ZAP!!! current flows through them.

    for the case of a cow, their legs are even further, therefore creating an even larger voltage gradient, a even more deadly one. i did some simple calculations. around a one foot interval, the change in potential can amount to few thousands volts(so the numbers i put in my diagram are kind of off, but the idea is there).

    get it?
    nope...you're still forgetting that electricity does not flow nicely in concentric circles...it follws the path of least resistence! man, where are you learning this...electricity does not behave the same way like when you drop a pebble in a bucket. it's free electricity and does not follow a text book drawing. electricity dissipitates through resistence and resistence causes heat. dissipitation was and never will be a cirlce or effected by standing on one leg. i know your drawing is a resemblence, but it's the resistence that matters and there are so many things that account for resistence. why is resistence important, because resistence will have a role in the amount of current, and it's the current that kills....which should tell you that if you now want to argue this point, then again it's not potential difference, but it now hinges on resistence.



    the best thnig to do...stay away from lightning

    no worries, i'm not mad. i know you understand the concept, but i've spent a long time understanding how to work safely around electricity and i don't think it's wise that you offer theories or other things that can get someone hurt.

  7. #67

    Default Re: Lightning @ NUS

    Quote Originally Posted by Hawaiisg View Post
    but it now hinges on resistence.
    Quote Originally Posted by satay16 View Post
    *but if the feet and point of lightning strike are collinear, it means that both feet are stepping on different equipotential lines. this causes a potential difference across the feet. how large is the potential you might ask. very very large. reason being the ground is of relatively high resistance, and the rate of decrease of potential is proportionate to the ground's resistance. so, it means that a small change in distance can cause a large potential difference. so, now, it becomes like having a few thousand volts of electricity across both feet, the further the separation of the feet, the more lethal the shock.

    please read my posts.

    and would you want me to draw? imperfect circles? just add uncertainty to my circles lah!
    Last edited by satay16; 29th March 2007 at 08:47 PM.

  8. #68

    Default Re: Lightning @ NUS

    okokok. so explain to me how ground strike kills people.

  9. #69

    Default Re: Lightning @ NUS

    Quote Originally Posted by satay16 View Post
    wrong. go read up on how ground strikes kills many cows with just one strike.
    yeah, you know why....because cows are most likely in pastures (wet or damp) and full of water and are most likely in the rain adding in to the factors...in other words the amount of resistence, humidity, ions, charges in the air, all added to their demise...these are the things that matter, not how many feet the cow was on which is my point. it's about air, location, resistence, and many others which are the real keys.

    anyways, no point here, i'm trying to help protect Csers....but in fairness to you and to hopefully to end this, if i see someone with a 70-200mm 2.8 lens taking photos in a lightning storm, i'll make sure to tell him go out and stand on one leg. after the flash and the smoke settles, hopefully his gear will still be working.

    i'll perform cpr.....camera permanently removed
    nice talking with you...

  10. #70

    Default Re: Lightning @ NUS

    Quote Originally Posted by Hawaiisg View Post
    yeah, you know why....because cows are most likely in pastures (wet or damp) and full of water and are most likely in the rain adding in to the factors...in other words the amount of resistence, humidity, ions, charges in the air, all added to their demise...these are the things that matter, not how many feet the cow was on which is my point. it's about air, location, resistence, and many others which are the real keys.

    anyways, no point here, i'm trying to help protect Csers....but in fairness to you and to hopefully to end this, if i see someone with a 70-200mm 2.8 lens taking photos in a lightning storm, i'll make sure to tell him go out and stand on one leg. after the flash and the smoke settles, hopefully his gear will still be working.

    i'll perform cpr.....camera permanently removed
    nice talking with you...
    actually, my argument is that in the case of a ground strike, someone standning on one leg will not be as injured as one who is standning on a voltage gradient.

    but for direct hits, if get hit, that's it. 99% will be pretty serious injury.

    i am not giving ideas about how to prevent getting hit. i am explaining why some people did not get injured by a ground strike while some other people does. about hopping on one leg, it is only true it one gets hit by a ground strike. in get hit by direct strike, then bye bye liao. it is meant as a joke, cos you cant choose to have a direct strike or ground strike to hit you. if can choose,..................woah.

    so i am ignoring other factors, because i am not typing a 20 page essay on how lightning works!! there are so many other factors other than those you stated. you expect me to type them out? no! it doesn't help in explaining why ground strike dun injure some people.
    Last edited by satay16; 29th March 2007 at 09:08 PM.

  11. #71
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    Default Re: Lightning @ NUS

    Quote Originally Posted by satay16 View Post
    actually, my argument is that in the case of a ground strike, someone standning on one leg will not be as injured as one who is standning on a voltage gradient.

    but for direct hits, if get hit, that's it. 99% will be pretty serious injury.

    i am not giving ideas about how to prevent getting hit. i am explaining why some people did not get injured by a ground strike while some other people does. about hopping on one leg, it is only true it one gets hit by a ground strike. in get hit by direct strike, then bye bye liao. it is meant as a joke, cos you cant choose to have a direct strike or ground strike to hit you. if can choose,..................woah.

    so i am ignoring other factors, because i am not typing a 20 page essay on how lightning works!! there are so many other factors other than those you stated. you expect me to type them out? no! it doesn't help in explaining why ground strike dun injure some people.
    makes me wonder... if ground strike, will the electricity travel from the big toe to the small toe then make your feet numb, then u fall on the floor, then the whole body surge from head to toe...
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  12. #72

    Default Re: Lightning @ NUS

    Quote Originally Posted by Del_CtrlnoAlt View Post
    makes me wonder... if ground strike, will the electricity travel from the big toe to the small toe then make your feet numb, then u fall on the floor, then the whole body surge from head to toe...
    actually, i had been thinking about this too just now. after some thoughts, i think my previous statement about lying on the ground is wrong. the person will feel something.

    let's try this simplification: imagine you are a length of high resistance wire(). so right now, we assume that the lightning strike and electricity travels along the ground. we extract radially part of this ground, and picture it as another high resistance wire with a current flowing through it.

    so, imagine you, the wire, hug the ground wire, effectively speaking, it is like adding another resistor in parallel, therefore causing a current to flow through you too.

    however, it is quite impossible to actually fall down and still get electricuted, cos lightning is really very fast. the time it takes to fall down is much slower than the time it takes for electricity to travel. well, unless the lightning strikes twice at the short interval.

  13. #73

    Default Re: Lightning @ NUS

    Yes, Satay is talking about ground strike. So Hawaiisg please don't be mistaken with direct hit. That's why you don't take cover under a tree or near a tall pole. Although u can ensure the lightning won't hit you, but when the lightning hit the tall object near you, the drift current on the ground will kill you.

    One thing I disagree with Satay is this sentence "the thing is you dunno where the lightning can hit, so the best deal is to actually lie on the ground, cos you will then become part of the ground. though the distance separation is large, every point on your body is at the same potential as the ground, therefore, no harm done."

    Every point same potential as ground does not mean no current will flow through the body. Imagine two resistors in parallel. No matter how much one resistor is than the other, some current will still flow through the higher resistance resistor. And it just takes a small current to kill you. The reason why lie on the ground is to reduce the height to reduce chance of direct hit (what Hawaiisg is talking about). And this method is only to be used if you are out in a big field with no shelter.

  14. #74

    Default Re: Lightning @ NUS

    Quote Originally Posted by theonlyone View Post
    Yes, Satay is talking about ground strike. So Hawaiisg please don't be mistaken with direct hit. That's why you don't take cover under a tree or near a tall pole. Although u can ensure the lightning won't hit you, but when the lightning hit the tall object near you, the drift current on the ground will kill you.

    One thing I disagree with Satay is this sentence "the thing is you dunno where the lightning can hit, so the best deal is to actually lie on the ground, cos you will then become part of the ground. though the distance separation is large, every point on your body is at the same potential as the ground, therefore, no harm done."

    Every point same potential as ground does not mean no current will flow through the body. Imagine two resistors in parallel. No matter how much one resistor is than the other, some current will still flow through the higher resistance resistor. And it just takes a small current to kill you. The reason why lie on the ground is to reduce the height to reduce chance of direct hit (what Hawaiisg is talking about). And this method is only to be used if you are out in a big field with no shelter.
    yes. i admitted my mistake it the post above yours.

    *woah, you come CS only posting kopitiam only ah? *

  15. #75
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    Default Re: Lightning @ NUS

    you peeps....
    relax lah...
    we not physicists leh...
    no need to explain so much about lightning theories.
    I wasn't struck by lightning & and so wasn't ac240v.
    just sharing what happened on wednesday since it was the closest encounter i've got with lightning.

    let's progress and Huat Ah!!!!
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  16. #76
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    Default Re: Lightning @ NUS

    Quote Originally Posted by mojopy View Post
    you peeps....
    relax lah...
    we not physicists leh...
    no need to explain so much about lightning theories.
    I wasn't struck by lightning & and so wasn't ac240v.
    just sharing what happened on wednesday since it was the closest encounter i've got with lightning.

    let's progress and Huat Ah!!!!
    no lah, they are discussing about new way to cook satay...

    probably going to electrocute satay next time... haven't decide on the voltage and ampere yet..
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  17. #77
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    Default Re: Lightning @ NUS

    hahaha.
    like this the satay man out of job le.
    we just buy the frozen satay then got lightning everyone rush out and point their satay upwards.
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  18. #78
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    Default Re: Lightning @ NUS

    Quote Originally Posted by mojopy View Post
    hahaha.
    like this the satay man out of job le.
    we just buy the frozen satay then got lightning everyone rush out and point their satay upwards.
    then mortuary will be very busy liao...
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  19. #79
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    Default Re: Lightning @ NUS

    Quote Originally Posted by Del_CtrlnoAlt View Post
    no lah, they are discussing about new way to cook satay...

    probably going to electrocute satay next time... haven't decide on the voltage and ampere yet..
    too many flame grill satay already, so lightning grilled satay

  20. #80
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    Default Re: Lightning @ NUS

    Quote Originally Posted by zcf View Post
    too many flame grill satay already, so lightning grilled satay
    actually we currently use low voltage high ampere to anneal our metal...

    and i think in US the electrocution sentence also do the same thing.... so i guess its in reality possible...

    but wonder which satay wanna volunteer....
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