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| Tags: problem, rigid, rod |
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#21
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On Tue, 23 Aug 2005 16:48:35 GMT, "Dirk Van de moortel"
wrote: wrote in message ... On Mon, 22 Aug 2005 16:19:22 GMT, "Dirk Van de moortel" wrote: wrote in message ... On Fri, 19 Aug 2005 16:27:39 GMT, "Dirk Van de moortel" wrote: wrote in message ... This problem is a combination of several problems I've posted in this group. When I combine the problems, the answers given to me in previous posts don't work. Here's the problem. Another everyday experience problem with 300000 km long rigid rods, I presume? http://users.pandora.be/vdmoortel/di.../Everyday.html Dirk, the link you posted has pandora.be in it, from which I infer refers to a country different than the United States of America. So I'm guessing English is not your native language. If you carefully read my sentence that you refer to in the above link, you will see that I stated that the 300000 km length IS NOT part of my everyday experience. Sure. I *had* carefully read your sentence and I understood it just the way you had intended it. It was one of the funniest things you ever wrote on this group. Well, with the velocity being only 3 meters / second, and the acceleration being only 1 g, I can experience how objects change (on a local level) when they move from one reference frame to another. For example, some posters in this group believe if the rod is made long enough, a person holding one end of the rod will be accelerated to a velocity approaching the speed of light. But with parameters like 3 meters / second and a 1 g acceleration it is easy for me to see that that notion is incorrect. You may think of that as being "an immortal fumble of David Seppala" but actually it helps me understand things easier. You're not one of those people who think one end of the rod travels at a speed close to the speed of light when it is placed on a conveyer belt moving at 3 meters / second, are you? Or is that why you label my approach as an immortal fumble? Just compare your | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." with "Your Honour, other than that bitchy wife of mine, I would never kill anyone, so surely you're not going to put me behind bars?" Dirk Vdm If you are going to add clauses in your analogy, why not something like: "Other than the rod being light-years in length, the parameters are values that occur in our daily experience, so surely I can learn something using parameters in the problem which are seen in my daily experience." Did you ever notice many posters twist the statements of others? David David In order for you not to think that I had misunderstood you line, I now have put emphasis on the entire sentence: | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." You can check it at: http://users.pandora.be/vdmoortel/di.../Everyday.html Hope this helps! Dirk Vdm |
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On 23 Aug 2005 11:07:01 -0700, "Spoonfed"
wrote: wrote: We recognize that sight and sound can be missleading and that no wrapping actually occurs. Wrapping actually does occur. In the rest frame of the rod and of the rotating cylinder, we are attaching one end of the rod to the cylinder a second before we attach the other end. The cylinder rotates 10 times before the other end is attached. Since the speeds are everyday values can actually do this experiment over a much shorter length. The short rod will attach to the short segment of the rotating disk, and if we attach one end at a different time then we attach the other end (the stationary frame view), the attached rod will spiral about the cylinder. In the problem I posted because of the lengths involved the spiral and wrapping occur over large distances, but it still occurs. David Right. If either of the two observers can be said to be measuring an illusion, it is the non-local observer, who measures the rod to be straight on a moving, length contracted, rotating cylinder. The geometry and forces which are actually holding the rod to the cylinder are local effects, and the rigidity of the coiled rod in the stationary frame. Aside: The nonlocal observer will only "see" the rod on the cylinder as straight if and when the rod passes directly in front of him, on a path perpendicular to his line of sight. Otherwise, differences in light propagation times between the front and back of the rotating cylinder will result in an image that does not perfectly represent the "present" in his frame of reference. When removing the rod/coil from the cylinder, you want to have a clamp that comes down on all portions of the rod at once in the nonlocal frame, and pulls it away from the cylinder with an instantaneous YOINK! What the clamp will look like from the rest frame is more like a zipper. In the stationary frame, the two edges of the clamp will not come down toward each other parallel, but at an angle, meeting at a point on the rod, gripping it, pulling it loose. The point would roll up the clamp edges as it passed by, pulling the rod loose as it goes. Since we have stiffened the rod, it will take considerably more force to remove the coiled rod than it took to put it on there. Quite possibly the clamp would simply fail to remove the the rod from the rotating cylinder, slipping off the rod instead of grabbing hold of it. I think your conundrum is that the rod appears to be straight in the nonlocal frame, and it has not been glued to the cylinder; it has not been increased in mass--it has only been stiffened. Why would stiffening a straight rod cause it to be harder to remove from a cylinder? Yes, so what is the explanation for observers in the moving frame, when all the contact points holding the rod to the cylinder are removed simultaneously? They do not measure any force on the rod, and therefore it should be a straight rod simply traveling off in the direction of the velocity it had when the contact points were eliminated. But that's not what happens in the stationary frame of the rotating cylinder and rod. David wrote: We recognize that sight and sound can be missleading and that no wrapping actually occurs. Wrapping actually does occur. In the rest frame of the rod and of the rotating cylinder, we are attaching one end of the rod to the cylinder a second before we attach the other end. The cylinder rotates 10 times before the other end is attached. Since the speeds are everyday values can actually do this experiment over a much shorter length. The short rod will attach to the short segment of the rotating disk, and if we attach one end at a different time then we attach the other end (the stationary frame view), the attached rod will spiral about the cylinder. In the problem I posted because of the lengths involved the spiral and wrapping occur over large distances, but it still occurs. David Right. If either of the two observers can be said to be measuring an illusion, it is the non-local observer, who measures the rod to be straight on a moving, length contracted, rotating cylinder. The geometry and forces which are actually holding the rod to the cylinder are local effects, and the rigidity of the coiled rod in the stationary frame. Aside: The nonlocal observer will only "see" the rod on the cylinder as straight if and when the rod passes directly in front of him, on a path perpendicular to his line of sight. Otherwise, differences in light propagation times between the front and back of the rotating cylinder will result in an image that does not perfectly represent the "present" in his frame of reference. When removing the rod/coil from the cylinder, you want to have a clamp that comes down on all portions of the rod at once in the nonlocal frame, and pulls it away from the cylinder with an instantaneous YOINK! What the clamp will look like from the rest frame is more like a zipper. In the stationary frame, the two edges of the clamp will not come down toward each other parallel, but at an angle, meeting at a point on the rod, gripping it, pulling it loose. The point would roll up the clamp edges as it passed by, pulling the rod loose as it goes. Since we have stiffened the rod, it will take considerably more force to remove the coiled rod than it took to put it on there. Quite possibly the clamp would simply fail to remove the the rod from the rotating cylinder, slipping off the rod instead of grabbing hold of it. I think your conundrum is that the rod appears to be straight in the nonlocal frame, and it has not been glued to the cylinder; it has not been increased in mass--it has only been stiffened. Why would stiffening a straight rod cause it to be harder to remove from a cylinder? Am I obligated to insult you now since I don't know the exact answer? Just kidding. I think the answer lies in the nature of the collisions--where the rubber meets the road, so to speak. If you look closely at the interactions and forces between the particles in the rod/coil, and in the clamp/zipper (in either frame), you'll find that they are more tightly bound to the cylinder after the rod has been stiffened. The analysis of exactly how the apparently straight rope attaches itself in the moving frame is still probably a fairly intricate problem. |
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wrote: On Tue, 23 Aug 2005 16:48:35 GMT, "Dirk Van de moortel" wrote: wrote in message ... On Mon, 22 Aug 2005 16:19:22 GMT, "Dirk Van de moortel" wrote: wrote in message ... On Fri, 19 Aug 2005 16:27:39 GMT, "Dirk Van de moortel" wrote: wrote in message ... This problem is a combination of several problems I've posted in this group. When I combine the problems, the answers given to me in previous posts don't work. Here's the problem. Another everyday experience problem with 300000 km long rigid rods, I presume? http://users.pandora.be/vdmoortel/di.../Everyday.html Dirk, the link you posted has pandora.be in it, from which I infer refers to a country different than the United States of America. So I'm guessing English is not your native language. If you carefully read my sentence that you refer to in the above link, you will see that I stated that the 300000 km length IS NOT part of my everyday experience. Sure. I *had* carefully read your sentence and I understood it just the way you had intended it. It was one of the funniest things you ever wrote on this group. Well, with the velocity being only 3 meters / second, and the acceleration being only 1 g, I can experience how objects change (on a local level) when they move from one reference frame to another. For example, some posters in this group believe if the rod is made long enough, a person holding one end of the rod will be accelerated to a velocity approaching the speed of light. But with parameters like 3 meters / second and a 1 g acceleration it is easy for me to see that that notion is incorrect. You may think of that as being "an immortal fumble of David Seppala" but actually it helps me understand things easier. You're not one of those people who think one end of the rod travels at a speed close to the speed of light when it is placed on a conveyer belt moving at 3 meters / second, are you? Or is that why you label my approach as an immortal fumble? Just compare your | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." with "Your Honour, other than that bitchy wife of mine, I would never kill anyone, so surely you're not going to put me behind bars?" Dirk Vdm If you are going to add clauses in your analogy, why not something like: "Other than the rod being light-years in length, the parameters are values that occur in our daily experience, so surely I can learn something using parameters in the problem which are seen in my daily experience." Did you ever notice many posters twist the statements of others? David David In order for you not to think that I had misunderstood you line, I now have put emphasis on the entire sentence: | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." You can check it at: http://users.pandora.be/vdmoortel/di.../Everyday.html Hope this helps! Dirk Vdm Hmmm, I've been watching your argument, and it seems to me that in this instance David is winning, but Dirk is getting a lot more laughs. In order to get the gist of relativity, I find it much more helpful to consider increasing the spatial scale, rather than trying to imagine time in terms of nanoseconds, and keeping a macro-scale or femtoseconds to introduce microscopic scale. My demonstration: http://www.spoonfedrelativity.com/files/relativity.swf is in real-time, with 1 second=1 second, using fanciful GSV's (Gargantuan Space Vehicles) which are hundreds of thousands of kilmoeters across. I included a note on the scale, stating: "On this page, the speed of light is 10 pixels per second. This means that each pixel must be 30,000 kilometers across. At this scale, the earth is just 1/3 of a pixel across and the sun is 46 pixels across. The actual distance between the sun and earth is 150 million kilometers, which would be about 10 times the width of the screen." Dirk, If I am not mistaken, you believe that beyond a certain length, distance loses its meaning due to wavering of the scale factor of the universe, or some effect of the cosmological constant, or ambiguities in simulteneity, right? If I understand right, this ambiguity is the main feature of the standard cosmological model, so you are in good company. Is this why you don't find it reasonable to consider the idea of a rotating cylinder 300,000 km long? |
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#27
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"Spoonfed" wrote in message ups.com... wrote: On Tue, 23 Aug 2005 16:48:35 GMT, "Dirk Van de moortel" wrote: wrote in message ... On Mon, 22 Aug 2005 16:19:22 GMT, "Dirk Van de moortel" wrote: wrote in message ... On Fri, 19 Aug 2005 16:27:39 GMT, "Dirk Van de moortel" wrote: wrote in message ... This problem is a combination of several problems I've posted in this group. When I combine the problems, the answers given to me in previous posts don't work. Here's the problem. Another everyday experience problem with 300000 km long rigid rods, I presume? http://users.pandora.be/vdmoortel/di.../Everyday.html Dirk, the link you posted has pandora.be in it, from which I infer refers to a country different than the United States of America. So I'm guessing English is not your native language. If you carefully read my sentence that you refer to in the above link, you will see that I stated that the 300000 km length IS NOT part of my everyday experience. Sure. I *had* carefully read your sentence and I understood it just the way you had intended it. It was one of the funniest things you ever wrote on this group. Well, with the velocity being only 3 meters / second, and the acceleration being only 1 g, I can experience how objects change (on a local level) when they move from one reference frame to another. For example, some posters in this group believe if the rod is made long enough, a person holding one end of the rod will be accelerated to a velocity approaching the speed of light. But with parameters like 3 meters / second and a 1 g acceleration it is easy for me to see that that notion is incorrect. You may think of that as being "an immortal fumble of David Seppala" but actually it helps me understand things easier. You're not one of those people who think one end of the rod travels at a speed close to the speed of light when it is placed on a conveyer belt moving at 3 meters / second, are you? Or is that why you label my approach as an immortal fumble? Just compare your | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." with "Your Honour, other than that bitchy wife of mine, I would never kill anyone, so surely you're not going to put me behind bars?" Dirk Vdm If you are going to add clauses in your analogy, why not something like: "Other than the rod being light-years in length, the parameters are values that occur in our daily experience, so surely I can learn something using parameters in the problem which are seen in my daily experience." Did you ever notice many posters twist the statements of others? David David In order for you not to think that I had misunderstood you line, I now have put emphasis on the entire sentence: | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." You can check it at: http://users.pandora.be/vdmoortel/di.../Everyday.html Hope this helps! Dirk Vdm Hmmm, I've been watching your argument, and it seems to me that in this instance David is winning, but Dirk is getting a lot more laughs. [snip] Dirk, If I am not mistaken, you believe that beyond a certain length, distance loses its meaning No, I don't. You are mistaken :-) And the idea is not to get laughs. I am *having* an incredible laugh over a statement like: | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." I think that David has another kind of sense of humour. Dirk Vdm |
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#28
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Dirk Van de moortel wrote: "Spoonfed" wrote in message Dirk, If I am not mistaken, you believe that beyond a certain length, distance loses its meaning No, I don't. You are mistaken :-) My error. You had a pretty explicit definition for length--only it was different than mine, because we disagreed about which version of "simultaneity" needed scare quotes. http://groups.google.com/group/sci.p...e=source&hl=en To understand your interpretation, I guessed that you calculated the "current" distance to faraway galaxies by first, switching to their reference frame and then calculating the distance to earth in their reference frame at the time when earth reaches its current proper time in their reference frame. Another method to do the same thing is by plotting out locations at times by using rapidity (v/sqrt(1-(v/c)^2) instead of velocity; multiplying the rapidity of the galaxy by the time on earth to find the distance. I'm not actually sure this is how you calculated the distances, but it seemed like whatever you were doing was getting this result. This makes some sense, because if we were to send them a message, they would regard it to have been sent from the earth in their reference frame, not in our reference frame, and it does create a nice infinite but expanding model. The only problem with it is that it's not what we see from here. And the idea is not to get laughs. I am *having* an incredible laugh over a statement like: | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." I think that David has another kind of sense of humour. Dirk Vdm Eh, 20 to 30 trillion kilometers? With length contraction, we can bring that down to only a few hundred billion. No biggie. I grant that it is humorous, but not necessarily a blunder. |
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#29
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"Spoonfed" wrote in message ups.com... Dirk Van de moortel wrote: "Spoonfed" wrote in message Dirk, If I am not mistaken, you believe that beyond a certain length, distance loses its meaning No, I don't. You are mistaken :-) My error. You had a pretty explicit definition for length--only it was different than mine, because we disagreed about which version of "simultaneity" needed scare quotes. http://groups.google.com/group/sci.p...e=source&hl=en To understand your interpretation, I guessed that you calculated the "current" distance to faraway galaxies by first, switching to their reference frame and then calculating the distance to earth in their reference frame at the time when earth reaches its current proper time in their reference frame. I remember the subthread. It was not about distances to galaxies. It was about whether it makes sense to wonder what time it is now somewhere else (concerning Mike's program iirc). Mike finds it an interesting question. Ben was saying that it never makes sense. I said something about it being totally useless when you are accelerating and useful when you are at rest w.r.t the remote location. I recall that you brought into the thread a bunch of unrelated technical issues in which I really wasn't interested, and so we ended up talking past each other. So I haven't really looked at what you write below about "current" distances... [skipping to the end] Another method to do the same thing is by plotting out locations at times by using rapidity (v/sqrt(1-(v/c)^2) instead of velocity; multiplying the rapidity of the galaxy by the time on earth to find the distance. I'm not actually sure this is how you calculated the distances, but it seemed like whatever you were doing was getting this result. This makes some sense, because if we were to send them a message, they would regard it to have been sent from the earth in their reference frame, not in our reference frame, and it does create a nice infinite but expanding model. The only problem with it is that it's not what we see from here. And the idea is not to get laughs. I am *having* an incredible laugh over a statement like: | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." I think that David has another kind of sense of humour. Dirk Vdm Eh, 20 to 30 trillion kilometers? With length contraction, we can bring that down to only a few hundred billion. No biggie. I grant that it is humorous, but not necessarily a blunder. This is not about lenght contraction of distances. This is about someone who has lost his mind decades ago over light-years long physical rods and manages to say without blinking: | "Other than the rod being light-years in length, the parameters are | values that occur in our daily experience." In my book it is exactly the same kind of blunder as: "Your Honour, other than that bitchy wife of mine, I would never kill anyone, so surely you're not going to put me behind bars?" But YBMV :-) Dirk Vdm |
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On 26 Aug 2005 07:33:58 -0700, "Spoonfed"
wrote: wrote: On 23 Aug 2005 11:07:01 -0700, "Spoonfed" wrote: wrote: We recognize that sight and sound can be missleading and that no wrapping actually occurs. Wrapping actually does occur. In the rest frame of the rod and of the rotating cylinder, we are attaching one end of the rod to the cylinder a second before we attach the other end. The cylinder rotates 10 times before the other end is attached. Since the speeds are everyday values can actually do this experiment over a much shorter length. The short rod will attach to the short segment of the rotating disk, and if we attach one end at a different time then we attach the other end (the stationary frame view), the attached rod will spiral about the cylinder. In the problem I posted because of the lengths involved the spiral and wrapping occur over large distances, but it still occurs. David Right. If either of the two observers can be said to be measuring an illusion, it is the non-local observer, who measures the rod to be straight on a moving, length contracted, rotating cylinder. The geometry and forces which are actually holding the rod to the cylinder are local effects, and the rigidity of the coiled rod in the stationary frame. Aside: The nonlocal observer will only "see" the rod on the cylinder as straight if and when the rod passes directly in front of him, on a path perpendicular to his line of sight. Otherwise, differences in light propagation times between the front and back of the rotating cylinder will result in an image that does not perfectly represent the "present" in his frame of reference. When removing the rod/coil from the cylinder, you want to have a clamp that comes down on all portions of the rod at once in the nonlocal frame, and pulls it away from the cylinder with an instantaneous YOINK! What the clamp will look like from the rest frame is more like a zipper. In the stationary frame, the two edges of the clamp will not come down toward each other parallel, but at an angle, meeting at a point on the rod, gripping it, pulling it loose. The point would roll up the clamp edges as it passed by, pulling the rod loose as it goes. Since we have stiffened the rod, it will take considerably more force to remove the coiled rod than it took to put it on there. Quite possibly the clamp would simply fail to remove the the rod from the rotating cylinder, slipping off the rod instead of grabbing hold of it. I think your conundrum is that the rod appears to be straight in the nonlocal frame, and it has not been glued to the cylinder; it has not been increased in mass--it has only been stiffened. Why would stiffening a straight rod cause it to be harder to remove from a cylinder? Yes, so what is the explanation for observers in the moving frame, when all the contact points holding the rod to the cylinder are removed simultaneously? They do not measure any force on the rod, and therefore it should be a straight rod simply traveling off in the direction of the velocity it had when the contact points were eliminated. But that's not what happens in the stationary frame of the rotating cylinder and rod. David You say the moving observers do NOT measure any force on the rod, but, I am saying there WILL be a measurable force holding the straight rod against the cylinder in the moving frame. After thinking some more, do you agree with me, now? I agree there is a measurable force holding the straight rod against the cylinder in the moving frame, but when each point of contact is eliminated at time t1 as measured in the moving frame, there is no longer any force acting on the rod. Each point of the rod continues in the direction it was traveling at the instance the point of contact was eliminated. The rod should remain a straight line as measured in the moving frame after each point of contact is eliminated. David My bad copy/paste work, and bad joke may have caused you to miss my last two paragraphs above: [Jesting deleted] I think the answer lies in the nature of the collisions--where the rubber meets the road, so to speak. If you look closely at the interactions and forces between the particles in the rod/coil, and in the clamp/zipper (in either frame), you'll find that they are more tightly bound to the cylinder after the rod has been stiffened. The analysis of exactly how the apparently straight rope attaches itself in the moving frame is still probably a fairly intricate problem. |
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