Wikipedia:Reference desk/Archives/Science/2015 September 9

= September 9 =

Pressure
What is the maximum bladder pressure that can be created by the human male and how does pressure correspond to urine trajexctory?--86.176.20.158 (talk) 19:22, 9 September 2015 (UTC)


 * These kinds of question will eventually get people sufficiently annoyed that it'll all end very badly. Since answering this is possible (but would require some research and some math) - it would be unfair to put people here to that much effort unless there is good reason.  So perhaps you'd be kind enough to tell us why you need to know.  Thanks! SteveBaker (talk) 19:43, 9 September 2015 (UTC)
 * My friends and I go out every saturday night drinking. Sometiems we have a contest against a wall. I would like to win one time.--86.176.20.158 (talk) 19:56, 9 September 2015 (UTC)


 * That's kind of troll-like questioning. I vote for closing this question. Where is that strange user with Greek name to do that? --Scicurious (talk) 20:15, 9 September 2015 (UTC)


 * Yes, close and hat. The greatest pressure is where the kidneys finally fail. Vesicoureteral reflux. Medical!--Aspro (talk) 20:59, 9 September 2015 (UTC)
 * You all are free to ignore this question. If you don't think the question is worth spending time on, then don't. I personally don't care for a lot of questions we get here, but that doesn't mean I have the right to prevent other people from answering if they wish. WP:NOTCENSORED. Additionally, we have no requirement that a question must be "serious" or "good enough". We answer all kinds of physics, language, math and entertainment questions that are asked for no other reason than idle fancy - and that is fine. So no, you don't have to like the question. But please do not disrupt our desks and prevent others from sharing references if they wish. And if anyone wants to close this question on grounds of content, they can expect a firm WP:TROUT. SemanticMantis (talk) 22:49, 9 September 2015 (UTC)


 * A pissing contest is a real thing, though today the phrase is more often heard metaphorically. I was not able to find many sources sharing strategy or techniques for maximum distance or height, but here is one youtube video I found that gives some tips and an illustration on "how to pee very far" . SemanticMantis (talk) 22:49, 9 September 2015 (UTC)
 * Supplementary Q: What is the best angle to aim for max distance and height?--86.176.20.158 (talk) 00:20, 10 September 2015 (UTC)
 * See ballistics. Height and distance are different goals, each with presumably a different optimal play and tactics for optimization. 45 degrees will give best distance for a given muzzle velocity if you ignore drag. One can easily spend hours researching this and making different approximations from different mathematical models. For this kind of question, first principles solutions are often time-consuming and imprecise; sometimes nothing beats old fashioned trial and error and empirical methods. While I can easily spend a few minutes defending your right to ask this question here and giving some general refs, that's about all the time I have to volunteer for now with my current WP:AGF :) SemanticMantis (talk) 02:41, 10 September 2015 (UTC)
 * Achieving maximum height can have unpleasant consequences.   D b f i r s   08:40, 10 September 2015 (UTC)
 * "Voluntary contraction of the abdominal muscles aids the expulsion of urine by increasing the pressure applied to the urinary bladder wall" (Urination)
 * This suggests that strong abdominal muscles are an advantage.
 * You won't reach maximum pressure at full bladder (because at equal force a bigger radius will result in lower pressure), so there's no advantage in overstretching your bladder (would probably have the opposite effect).
 * High heels will add distance and height. ;-)
 * Tightening your belt right before you start might help. Ssscienccce  (talk) 14:03, 10 September 2015 (UTC)

Electric shocks
In all those TV shows where the villain is administering electric torture and tells the technician "increase the power!" — what is he increasing? This very simple definition of volts, amps, and watts, would suggest that it's either voltage or amperage, probably amperage. 3-way lamps would support this theory, considering a typical lightbulb says something like "30/70/100W, 120V", or in amps "250/583/833mA, 120V" (I think). So, is that right? Eman 235 / talk 21:54, 9 September 2015 (UTC)


 * In all those TV shows, the villain is not increasing anything, it's just the actor acting more distressed. For real uses of electricity not as a source of power see Electric_shock, and Electric_shock. --Scicurious (talk) 22:24, 9 September 2015 (UTC)


 * Of course. I meant, in theory, what would they be increasing? From the article: "...the received voltage and current can be controlled with precision and used to cause pain and fear without always visibly harming the victim's body." Is "current" referring to amperage? Which would be more likely to be increased? Eman 235 / talk  22:38, 9 September 2015 (UTC)


 * With a variable power supply, what is normally controlled is the mean voltage. (It may be reduced from the maximum by using a potentiometer (a variable resistor), or by switching resistors into the circuit, or by using a chopper that rapidly turns the circuit on and off for varying amounts of time.)  This all happens within the power supply.  In the case of torture (or more benignly, when operating something like a model railway or a variable-speed drill), the resistance of the load (the victim) is essentially constant; therefore, raising the voltage also raises the current (amps) and the power (watts).


 * This is different from a 3-way light bulb, where there are two separate loads (two filaments) that are switched into and out of the circuit. They operate on a fixed voltage, but the current and the power will very according to which setting is chosen.


 * By the way, in Stanley Milgram's famous (or notorious) experiment in obedience to authority, when people thought they were administering electric shocks, the apparatus was calibrated in terms of voltage. So this was one thing about the experiment that was realistic.  --65.95.178.150 (talk) 23:03, 9 September 2015 (UTC)


 * On the other hand, if the current is very low people can withstand voltages in the 10s of kV range with no ill effects or even discomfort. Demonstrations with Van de Graaff generators are a familiar example. Short Brigade Harvester Boris (talk) 00:28, 10 September 2015 (UTC)


 * True. So if you were the bad guy in this scenario, that's not the sort of power supply you'd use. Well, unless you were an incompetent bad guy. --65.95.178.150 (talk) 03:09, 10 September 2015 (UTC)


 * Voltage, current and power are not independant variables. --DHeyward (talk) 01:13, 10 September 2015 (UTC)


 * Yeah, exactly. V=IR (ohms law) which is to say that voltage = current x resistance, or volts = amps x ohms.  Since the resistance of the victim (in ohms) will probably be pretty much constant, it is meaningless to say whether you're increasing the volts or the amps because one depends on the other in direct proportion.  The actual knob may be calibrated in volts or amps depending on what kind of power supply you're using - but the net effect is the precisely the same.  If you double the voltage, then the current also doubles.  Power (in Watts) is volts times amps - so again if the resistance is constant (which it pretty much is) - then doubling the voltage doubles the amperage which together quadruple the wattage - but you can't increase the power (wattage) without increasing both the voltage and the amperage (current).
 * So just about the only thing you can say here is that if the villain is increasing the power by 10%, he's probably not causing as much pain/damage as if he increased the voltage or the current by 10% because the latter would increase the power by 21%
 * SteveBaker (talk) 01:59, 10 September 2015 (UTC)


 * Except that he's probably using "power" as an ordinary English word meaning electricity, not in the technical sense in physics as you are, and he probably is measuring the amount of "power" by the voltage. --65.95.178.150 (talk) 03:09, 10 September 2015 (UTC)


 * In that sense, power is V^2/R. --DHeyward (talk) 06:00, 10 September 2015 (UTC)
 * That's the same thing, not some 'different sense' of the word! If (as you say) power=V.V/R and then (because ohms law says V=I.R) I can substitute one of the V's for I.R and get V.I.R/R, the R's cancel and we end up with power=V.I - which is exactly what I said it was.  There isn't some 'different' meaning. SteveBaker (talk) 02:43, 11 September 2015 (UTC)
 * Sigh. In ordinary English usage, as I said, "power" does have other meanings.  I was talking about sense 6a here; you're talking about sense 6c as if it was the only one. --65.95.178.150 (talk) 03:57, 11 September 2015 (UTC)
 * I agree with you - I was pointing out to DHeyward that his/her interpretation of what you said is in no way different from what I said. V2/R is the same as V.I which is just the physics meaning of 'power'...not the alternative sense that you are suggesting. SteveBaker (talk) 05:52, 12 September 2015 (UTC)


 * Thanks for all these replies! So basically they are supposed to be increasing the voltage? Eman 235 / talk  03:36, 10 September 2015 (UTC)
 * No, it can be voltage or current or power but they aren't independent. You can call for increasing current or increasing voltage.  Either is fine and there are both current sources (will hold a specific current regardless of voltage) and voltage sources (will hold a specific voltage regardless of current).  And if you go up in frequency where S parameters dominate, power is what's constant and voltage and current vary spatially.  (Radar, for example is specified in power, not voltage or current - so will the crowd control millimeter wave devices).  Tasers work by limiting charge delivery and voltage and current are part of a total energy delivery from a capacitor (qV).  --DHeyward (talk) 05:58, 10 September 2015 (UTC)


 * Frequency is certainly another parameter (if this is alternating current) - and that will certainly make a difference to the pain/damage involved. But when you talk about the voltage (and hence the current) of AC electricity, you have to be careful about whether you're talking about the average voltage (which is zero) or the peak voltage - or the 'RMS' voltage.


 * You can also consider very brief pulses of electricity - the human body isn't going to do well with (say) 240 volts applied to it for multiple seconds - but you can touch something with a static-electrical charge up at tens of thousands of volts and get a brief, painful (but mostly harmless) "zap".


 * Another parameter is the way the electricity is conducted into the body - a shock between thumb and forefinger of one hand is unlikely to do much more than produce burns - but a shock between one hand and the other crosses the heart and that's much more likely to be fatal.


 * Yet another consideration is whether the skin is intact. Our skin has a reasonably high resistance - and because V=IR, you don't get much current flowing for some particular voltage.  However, there is one case on record of a man who died from the shock from a nine volt battery!  He'd been holding a pair of sharp probes that had penetrated the skin and there was a direct path through the blood across his heart.  Blood being mostly salty water, has a very low resistance.  So in that case, the resistance term in V=IR was a very small number and even though the voltage was relatively small (9 volts), the current was high and that was enough to do him in.  http://www.darwinawards.com/darwin/darwin1999-50.html - it's important to understand this relationship because it's all too easy to assume that anything under a couple of dozen volts is "safe" - and that's certainly not the case.


 * SteveBaker (talk) 02:43, 11 September 2015 (UTC)


 * I've always doubted the accuracy of that particular story of the fatal multimeter shock, since the multimeter has series resistance, and it would not be that easy to stick multimeter test leads through one's skin. But I am delighted if some torturer thinks that a 9 or 12 volt battery is a good torture tool and does not result to higher voltage. As for static shocks, I have found the discharge of a large Van de Graff generator to be very painful, just like the discharge of a large capacitor. I caution against experimenting with painful electric shocks. As for the painfulness of a DC or AC shock there are tables showing the minimum current to be detectable, then the current to be painful. A constant current device can be used, which is basically a high voltage with a series high resistance to limit current, or an actively regulated current source. Then the resistance of the dry or moist skin, or of the underlying tissue is less of a factor in determining the current. If the resistance of the preparation were too high, of course, and the voltage were raised enough to maintain current, then in the limit there would be high temperature arcing and burning, like a malfunctioning electric chair, which would be a different sort of pain. That said, I recall that before cryosurgery and lasers doctors once had  a little electric device in their offices to burn off warts with an electric arc. and people were able to bear it. Edison (talk) 16:48, 11 September 2015 (UTC)
 * Yeah, I know it seems unlikely - and we've debated the authenticity of the story many times before - but there is a claim of evidence in the form of a 1999 US Navy Safety publication that confirms it - and if you read the reference fully, there are people with good explanations for why the series resistance of the meter didn't save him. It would be nice to find that publication and put this to bed once and for all. SteveBaker (talk) 18:43, 11 September 2015 (UTC)


 * People have been able to bear many forms of "professional" zapping over the years. If it weren't for experimenting with electric shocks, your namesake (or Frankenstein's) wouldn't be a namesake. No pain, no gain. But yes, I'd advise potentially powerful people shouldn't shock themselves. That'd hurt! InedibleHulk (talk) 17:52, 11 September 2015 (UTC)


 * Overly detailed! Haha. But it's all very interesting, in a morbid sort of way. Eman 235 / talk  00:42, 12 September 2015 (UTC)