3 ms·

> Even before the steady state is achieved, there is an energy-transferring chain of physical cause-and-effect that is moving (at limited speed, ~c) along the w

> Even before the steady state is achieved, there is an energy-transferring chain of physical cause-and-effect that is moving (at limited speed, ~c) along the wire (but not all around the wire loop yet)... [my emphasis.] Well, yes, that's one of the points being made in the original video! > At the same, time, there is a different, smaller electric field "leaking" through the air/void in a straight line from the battery to everywhere else, which will reach the lightbulb much sooner in the original configuration, and of course this is also carrying some energy. Well, yes, that is one of the other points being made in the original video! And those effects are not so small as to be trivial - check out the numbers in the example I have provided. Sound is rather different than EM, so one should be careful in arguing from analogies, even if it seems to give the correct answer. Why not just go with the very well-established EM formulae for this situation? in your other reply (https://news.ycombinator.com/item?id=29935760 https://news.ycombinator.com/item?id=29935760) you are essentially saying of course this is all correct! - but the mere fact that this video prompted half a dozen or more videos in response (of wildly varying quality - some of them are laden with non-sequiturs about what would happen in different experiments) indicates that a nontrivial point is being made here, that seems counterintuitive for many people. Given that you are confirming the main points of the video, it is not clear to me why you would call it "extremely misleading, if not technically wrong." In your other reply, you claim that Veritasium is deliberately obscure, but it is not clear to me that one can even make much of a case for him being accidentally less straightforward than he could have been, from this evidence.

tsimionescu 5y ago
I say that he is misleading because of a few points: - he claims the chain analogy is a lie, even though it gives the exact right intuition about the effects. He also obscures the intuition by asking why the energy doesn't go back and forth if the engine pulls the chain back and forth, which is nonsense. - he phrases everything in a way that, to me, suggests that the energy is flowing directly from producer to consumer, when in fact energy is flowing on two separate pathways - radially away from the producer, and along the wires. Energy flow doesn't change if the consumer isn't there, though he seems to me to imply that it does. - he claims that energy flows "outside the wires" and shows diagrams of the Poynting vectors all-around the circuit, but doesn't show that energy flow quickly decreases with distance from the wires, at least for the DC case - he claims that what's happening inside the wires (the movement of the electrons) is not that important, when in fact it is the very movement of those electrons that generates the magnetic field, and the initial moving electric field Overall, the video very explicitly tells you that the movement of the electrons and the chain analogy are wrong and mostly irrelevant to how power is actually transmitted in an electric circuit, which is simply wrong and misleading - even though the fields are an important part, they are intrinsically connected to the movement of electrons, and the chain analogy is pretty good at showing that (a compressive wave analogy would be even closer in some ways). It's also important to note that you are the one talking about transmission line theory - the Veritassium video doesn't, and exclusively talks about Poynting vectors as an explanation, which would make it very hard to come up with a quantitative explanation of the phenomenon.
- mannykannot 5y ago
  I take your point that Veritasium himself did not analyze the scenario as a transmission line, and he would probably have been clearer if he had done so. Also, in several places here, you say that you took him as saying this or that, and if that is how you (and probably others) saw it, then he could have been clearer by anticipating and explicitly addressing those concerns. In addition, it was probably a mistake to present it as an issue of whether a bulb of the sort he showed would light up, given how many people got distracted by that detail. Therefore, I accept that the video could have been clearer, but I still see no reason at all to accuse Veritasium of being deliberately misleading. On the other hand, the thing about the chain analogy is that it is not "nonsense", as you put it, to point out that it is not the complete picture in general, it is not an "exact" intuition, and, most relevantly here, that it completely fails to explain what happens in this case in the period of interest, prior to the arrival of the reflected wave back to the origin and the establishment of a steady state. Furthermore, one can not get the correct answers - or the correct intuitions, for that matter - from any model that assumes the energy flows only where the charges are moving (this was a roadblock in understanding electromagnetism which was broken by Maxwell introducing the displacement current.) Therefore, Veritasium had good pedagogical reasons for saying that the chain model is not accurate and for introducing the Poynting vector. As I pointed out in my previous post, your previous post consisted of a series of points in which you were saying, in effect, that Veritasium was correct, and if you want to reverse course on that now, I think you owe us an explanation of how the chain model explains what happens in the first second after the switch is turned on.
  - tsimionescu 5y ago
    > As I pointed out in my previous post, your previous post consisted of a series of points in which you were saying, in effect, that Veritasium was correct, and if you want to reverse course on that now, I think you owe us an explanation of how the chain model explains what happens in the first second after the switch is turned on. It depends what level of detail you want to explain. The chain model explains pretty well what happens in the steady state of the circuit, as long as we take the chain links to represent EM waves and not actual electrons. It also suggests that the motor starting to move the chain will cause some amount of motion to happen at the middle point by radiating mechanical waves through the air/ground. This explanation is actually equivalent to the amount of detail that can be gleaned from Veritassium's video - since his explanation also doesn't give (a) any quantitative description nor (b) any idea of what kind of motion/energy is being transmitted. Of course, the chain analogy is nowhere near good enough compared to the transmission line explanation. Apart from the quantitive issue, the biggest weakness is that it predicts some kind of random motion, whereas the actual transmission line model predicts a current in the same direction as the final wore current. A closer mechanical analogy which might actually have the necessary features (though definitely highly dampened) would be using a loud speaker and a water pipe. The loudspeaker will send a mechanical wave through the water pipe which will travel at the speed of sound through water, whereas water molecules will move in the same direction but much slower, similar to the real electron movement. Secondly, the sound waves will also travel through air and quickly reach the mid point of the pipe, and here they should actually cause a smaller sound wave to start traveling through the pipe from that point as well, in the same direction that the final wave will travel. The magnitude of the effect will be much smaller than in the EM case, but the other characteristics should be similar. In fact, this sound-wave-in-water-pipe model would also predict the right phenomenon if you had two close parallel unconnected pipes, and were sending a sound wave through one of them - the sound wave would be transmitted across the gap and through the second pipe as well, even if the source were far away. The chain model might predict something similar here, but at a rate that is below our normal ability to notice, and thus outside our regular intuition.

tsimionescu 5y ago

I say that he is misleading because of a few points: - he claims the chain analogy is a lie, even though it gives the exact right intuition about the effects. He also obscures the intuition by asking why the energy doesn't go back and forth if the engine pulls the chain back and forth, which is nonsense. - he phrases everything in a way that, to me, suggests that the energy is flowing directly from producer to consumer, when in fact energy is flowing on two separate pathways - radially away from the producer, and along the wires. Energy flow doesn't change if the consumer isn't there, though he seems to me to imply that it does. - he claims that energy flows "outside the wires" and shows diagrams of the Poynting vectors all-around the circuit, but doesn't show that energy flow quickly decreases with distance from the wires, at least for the DC case - he claims that what's happening inside the wires (the movement of the electrons) is not that important, when in fact it is the very movement of those electrons that generates the magnetic field, and the initial moving electric field Overall, the video very explicitly tells you that the movement of the electrons and the chain analogy are wrong and mostly irrelevant to how power is actually transmitted in an electric circuit, which is simply wrong and misleading - even though the fields are an important part, they are intrinsically connected to the movement of electrons, and the chain analogy is pretty good at showing that (a compressive wave analogy would be even closer in some ways). It's also important to note that you are the one talking about transmission line theory - the Veritassium video doesn't, and exclusively talks about Poynting vectors as an explanation, which would make it very hard to come up with a quantitative explanation of the phenomenon.

mannykannot 5y ago
I take your point that Veritasium himself did not analyze the scenario as a transmission line, and he would probably have been clearer if he had done so. Also, in several places here, you say that you took him as saying this or that, and if that is how you (and probably others) saw it, then he could have been clearer by anticipating and explicitly addressing those concerns. In addition, it was probably a mistake to present it as an issue of whether a bulb of the sort he showed would light up, given how many people got distracted by that detail. Therefore, I accept that the video could have been clearer, but I still see no reason at all to accuse Veritasium of being deliberately misleading. On the other hand, the thing about the chain analogy is that it is not "nonsense", as you put it, to point out that it is not the complete picture in general, it is not an "exact" intuition, and, most relevantly here, that it completely fails to explain what happens in this case in the period of interest, prior to the arrival of the reflected wave back to the origin and the establishment of a steady state. Furthermore, one can not get the correct answers - or the correct intuitions, for that matter - from any model that assumes the energy flows only where the charges are moving (this was a roadblock in understanding electromagnetism which was broken by Maxwell introducing the displacement current.) Therefore, Veritasium had good pedagogical reasons for saying that the chain model is not accurate and for introducing the Poynting vector. As I pointed out in my previous post, your previous post consisted of a series of points in which you were saying, in effect, that Veritasium was correct, and if you want to reverse course on that now, I think you owe us an explanation of how the chain model explains what happens in the first second after the switch is turned on.
- tsimionescu 5y ago
  > As I pointed out in my previous post, your previous post consisted of a series of points in which you were saying, in effect, that Veritasium was correct, and if you want to reverse course on that now, I think you owe us an explanation of how the chain model explains what happens in the first second after the switch is turned on. It depends what level of detail you want to explain. The chain model explains pretty well what happens in the steady state of the circuit, as long as we take the chain links to represent EM waves and not actual electrons. It also suggests that the motor starting to move the chain will cause some amount of motion to happen at the middle point by radiating mechanical waves through the air/ground. This explanation is actually equivalent to the amount of detail that can be gleaned from Veritassium's video - since his explanation also doesn't give (a) any quantitative description nor (b) any idea of what kind of motion/energy is being transmitted. Of course, the chain analogy is nowhere near good enough compared to the transmission line explanation. Apart from the quantitive issue, the biggest weakness is that it predicts some kind of random motion, whereas the actual transmission line model predicts a current in the same direction as the final wore current. A closer mechanical analogy which might actually have the necessary features (though definitely highly dampened) would be using a loud speaker and a water pipe. The loudspeaker will send a mechanical wave through the water pipe which will travel at the speed of sound through water, whereas water molecules will move in the same direction but much slower, similar to the real electron movement. Secondly, the sound waves will also travel through air and quickly reach the mid point of the pipe, and here they should actually cause a smaller sound wave to start traveling through the pipe from that point as well, in the same direction that the final wave will travel. The magnitude of the effect will be much smaller than in the EM case, but the other characteristics should be similar. In fact, this sound-wave-in-water-pipe model would also predict the right phenomenon if you had two close parallel unconnected pipes, and were sending a sound wave through one of them - the sound wave would be transmitted across the gap and through the second pipe as well, even if the source were far away. The chain model might predict something similar here, but at a rate that is below our normal ability to notice, and thus outside our regular intuition.