|
crazyml -> RE: Potentially dangerous activities (5/11/2010 1:56:30 AM)
|
quote:
ORIGINAL: pompeii
quote:
ORIGINAL: crazyml
quote:
ORIGINAL: pompeii
Just to be clear, if you punctured each of your thumbs with a needle and pressed a normal 1.5VDC D cell battery into it, your heart would stop instantly
Just to be clear, this is utter, utter nonsense.
Hi crazyml,
Do me a favor. Think before you post.
Better yet, take your 9v alkaline-battery ohm meter, puncture each of your thumbs with it, and tell us what happens.
Lem'me guess. You'll win a Darwin award. Just like this guy in the US Navy did.
http://www.darwinawards.com/darwin/darwin1999-50.html
Pompeii
PS: You sound like the guy who wrote to me in my CM email saying that no way could a rechargeable battery be more dangerous than an alkaline battery because, he said, the voltage is even lower in a rechargeable battery. Of course, I reminded him of the "internal resistance" of a battery, which is what limits the current sourcing ability of the battery - which I'm sure he never even heard of. Point is, if you're gonna be stupid, don't try it with me please.
AH! Now it's a nine volt battery? So you felt it necessary to up the voltage by a factor of six? And it's still nonsense.
You were good enough to let me know that you have a degree in Bio-med and that you know for a fact that the resistance from thumb to thumb through the heart is 50ohms. You also took the time to observe that I'm an idiot.
If I may, I'll deal with the physics, and then address my idiocy.
First, let's look at the question of resistance. I think you should write up the research you did that allows you to make his claim:
quote:
Assume the resistance of your blood from thumb to thumb through the heart is about 50 ohms (I know the Darwin award says it's higher but I have a degree in biomedical engineering and I know it to be around 50 ohms)
This is a startling new revelation for science, and it may well earn you some kind of prize. You see it is generally believed that the internal resistance (ie discounting the resistance of the skin) of the body is somewhere between 300 and 1000 ohms. Take this research paper from the journal nature - (http://www.nature.com/nature/journal/v60/n1550/pdf/060245a0.pdf) I'm assuming, given your evident erudition and your professional qualifications that you've probably got a subscription, but even if you haven't, you'll see that the resistance of blood, measured at a temperature of 60f, was found to be 550 ohms. I'm sure, since you're familiar with research techniques, that you'll also immediately note that in this experiment it seems that the electrodes were 75mm apart.
Your discovery that the resistance between thumb and thumb is in fact ten times lower than the science suggests is, well let's say "startling".
I'm just as certain that you're familiar with the fact that resistance is also a factor of length and cross-sectional area. This is wonderfully explained here (http://en.wikipedia.org/wiki/Resistivity).
The formula (and I only repeat this for the information of others, since I've no doubt you could do all this with your eyes closed) is;
R = p * l/a
(Where R is resistance, p is the static resistivity, l is the length and a is the cross sectional area.)
So very roughly speaking you can assume that given the same coss-sectional area if the resistance of blod over 75mm is 550 ohms the resistance of blood over a distance of 150mm will be 1100ohms. Now I have short stubby arms (and this is a bit rough, as I've had to use an old tape measure that's in inches and then clumsily convert to mm) and the distance I get is around 1600mm. Oh my... that's like 10 times farther than the 150mm that gave us 1050ohms. So now we're looking at something close to 11000ohms.
So, you can understand my excitement at your discovery - Your blood is 2000 times less resistant than regular blood!
Of course, you'll immediately want to point out that the cross-sectional area isn't constant - and you'll be absolutely right, the current will flow through the whole of the body, some will find its way to the skin, some will flow through bone, some through muscular tissue, and indeed a good proportion of the current will completely bypass the heart itself. I'm afraid I couldn't even take a stab at this one but let's see if we can agree that blood is the least resistive (I'm pretty sure that bone and muscle don't conduct electricity as well as good old blood). So I'm really looking at the worst case here - I'm assuming that you've jammed those probes into a proper full on artery/vein (my brain would explode if I had to figure out the average cross-sectional area of those teensy capillaries!)...
So now let's do V = IR.
We know V, it's 1.5. And we know R, it's (and I'm rounding it down for simplicity) 10000, so we're talking about 0.15 milliamps.
Holy crap! That would be nothing. Let's back off... let's say the total internal resistivity is just the 550 measured using a pot of blood with the probes 75mm apart - sheesh, that only cranks it up to 2.72milliamps.
But wait a second, you took the time to email me to tell me that I'm just an idiot,... and yet it seems your sums were out by like 2000 times! Or a little over 10 times if we assume that you're really really little and the distance between your thumbs is 75mm.
So now I'm pretty sure I've properly nailed that canard - and please, correct me if I'm wrong! Onto the "idiocy" thing.
I am often idiotic, and when I am it's either deliberate (I'm being a jackass on purpose), or because I've made a stupid stupid mistake. In the latter case, I'm really happy to be corrected - it helps me grow. So if someone challenges me in a forum, I'll either ignore it (you can't please everyone!) or I'll get into google and take the trouble to learn. I would never, ever, stoop to sending someone a whining email, because that's just pathetic.
[Edited to add the following disclaimer]
As usual, on re-reading my post I noticed a couple of typos. Why I can't proof my posts before I submit them I don't know - but on this occasion, I'm not going to go back and sub it, on account of my not giving a shit.
[Edited to add the following]
Oh and, rest assured, I wasn't the person who emailed you about the difference between a rechargeable battery and an alkaline battery (I certainly don't give enough of a shit to make that kind of distinction!)
|
|
|
|
