I was reading this about those 3 electrical lines in Ohio that are suspect in the big blackout.
PLEASE... someone please tell me this is reporting gone insane.. electricity has weight??
........... A spokesman for First Energy confirmed that company facilities in northern Ohio had suffered several mishaps during the afternoon of the 14th. These included a tree falling on one of the company�s heavy-duty 345-kilovolt high-tension lines and �tripping off� a generator at a company plant in Eastlake, Ohio. Industry sources said another 345kv line may have been so overloaded with electricity that it sagged into a lower-voltage cable below it on the pylon, shorting out the circuit. (A company spokesman acknowledged that one of its lines could have sagged.) ...........
PLEASE... someone please tell me this is reporting gone insane.. electricity has weight?? Well, sort of. The number of electrons in the line is essentially constant. In any given segment of wire, as many electrons flow in as flow out. So mass (hint - reast mass) remains constant. However, the more current you have, the stronger the magnetic fields surrounding the wire. And if it's AC power (which it usually is) there are also electric fields, as the changing current produces changing magnetic fields which produce changing electric fields which produce changing magnetic fields... etc. So anyway, there's a certain amount of energy desnity in the fields surrounding these wires. And thanks to E=mc<sup>2</sup> this energy is equivalent to a certain very small amount of relativistic mass. Which is a long way of say ing that yes, the wires probably have some added weight to them when there's a large current going through them. Ummm, I think. Not sure how gravitation on EM fields gets translated back into force on the wires carrying the current. But it sounds at least plausible to me. However, this effect should be incredibly, extremely small. No way it would account for enough added weight to justify sagging. Rather, I suspect the explanation is far more mundane. My guess is: high current leads to increased temperature in the wires, which causes thermal expansion, which causes the wires to grow slack. Which is not quite as sexy as relativistic mass, but has the added benefit of being plausible. [ August 17, 2003: Message edited by: Jim Yingst ]
Whew Jim ! I'm glad you explained that! As I've been filling up my laptop's hard drive over the last several months I've been noticing that my laptop seems to be getting HEAVIER! I'm thinking it's all those 1 bits, which have to be just a LITTLE bit heavier than the 0 bits! It may not seem like much, but we're talking gigs and gigs of bits, so they might really add up! I will rest easier tonight!
Spot false dilemmas now, ask me how!
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Moving current generates a magnetic field. Two moving currents (ie two lines) generate twice the attraction. Greater current means more attraction. I'm only aware of the effect in parallel power lines, which is why the spacing between the lines and the slack in overhead lines is designed so they should never be able to touch. I would have thought it was more likely the high voltage line 'lifted' the low valtage line than the low votage line causing the high voltage line to sag. This is a very real effect and more probable
posted 16 years ago
Moving current generates a magnetic field. Two moving currents (ie two lines) generate twice the attraction. Twice as much as... zero? If there were only one current there'd be no attraction at all, given that there's nothing to attract to (or from, depending on your perspective). But yeah, parallel currents do attract each other. Unless they're in opposite directions, in which case they repel. I guess they must arrange the lines to try to distribute the forces between different lines in the least troublesome manner possible, but doubtless there's no perfect solution to this. Good catch. I would have thought it was more likely the high voltage line 'lifted' the low valtage line than the low votage line causing the high voltage line to sag. Why's that? Whatever the force is between the two, it's equal and opposite between the two of them, right? In any event I'd think that if the problem was caused by attraction between the two wires, they probably both moved toward each other. This is a very real effect and more probable Than the relativistic mass effect I mentioned? Absolutely, that was just me being silly. (Well it's real, but insignificant.) More probable than thermal expansion? Maybe, dunno, either one seems plausible offhand; wouldn't surprise me if both were factors. Probably the magnetic attraction is the primary effect and thermal expansion helps loosen things up. Thanks for pointing it out. [ August 18, 2003: Message edited by: Jim Yingst ]
Jim: And thanks to E=mc2 this energy is equivalent to a certain very small amount of relativistic mass. ... However, this effect should be incredibly, extremely small. No way it would account for enough added weight to justify sagging. Suppose that the energy of the field around the wire has increased by some multiplier as a result of the power surge. Wouldn't it follow from E=mc2 that the relativistic mass of the wire has also increased by that multiplier?
posted 16 years ago
Sure. But multiplying an incredibly small number by two or ten or whatever the power surge provided will most likely still give an incredibly small number.
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