Bug and rivet paradox
in [Relativity]
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From: Edward Green on 12 Jun 2010 19:14 I'm puzzled by some aspects of the bug and rivet paradox http://hyperphysics.phy-astr.gsu.edu/Hbase/Relativ/bugrivet.html Evidently the rivet definitely hits the bottom of the hole, because this is seen in the rivet's frame, and hence must be an event observable in any frame. Also, evidently, the head of the rivet hits the plate, since this is observable in the plate's frame, and hence must be an event observable in any frame. What I'm puzzled about is the intermediate descriptions: in the rivet frame, a compressional wave travels up the shaft of the rivet until the plate hits the head. In the plate frame, a _dilational_ wave seems to travel down the rivet from the opposite direction until the foot of the rivet hits the backstop. How to reconcile these descriptions?
From: blackhead on 12 Jun 2010 23:45 On 13 June, 00:14, Edward Green <spamspamsp...(a)netzero.com> wrote: > I'm puzzled by some aspects of the bug and rivet paradox > > http://hyperphysics.phy-astr.gsu.edu/Hbase/Relativ/bugrivet.html > > Evidently the rivet definitely hits the bottom of the hole, because > this is seen in the rivet's frame, and hence must be an event > observable in any frame. > > Also, evidently, the head of the rivet hits the plate, since this is > observable in the plate's frame, and hence must be an event observable > in any frame. > > What I'm puzzled about is the intermediate descriptions: in the rivet > frame, a compressional wave travels up the shaft of the rivet until > the plate hits the head. In the plate frame, a _dilational_ wave seems > to travel down the rivet from the opposite direction until the foot of > the rivet hits the backstop. How to reconcile these descriptions? The velocity of a particle is also frame dependent. I don't see why there is a need to reconcile events measured differently in different frames.
From: Inertial on 13 Jun 2010 00:19 "blackhead" <larryharson(a)softhome.net> wrote in message news:5033df94-68e4-49c9-91b1-0e1f0197172a(a)w31g2000yqb.googlegroups.com... > On 13 June, 00:14, Edward Green <spamspamsp...(a)netzero.com> wrote: >> I'm puzzled by some aspects of the bug and rivet paradox >> >> http://hyperphysics.phy-astr.gsu.edu/Hbase/Relativ/bugrivet.html >> >> Evidently the rivet definitely hits the bottom of the hole, because >> this is seen in the rivet's frame, and hence must be an event >> observable in any frame. Yeup >> Also, evidently, the head of the rivet hits the plate, since this is >> observable in the plate's frame, and hence must be an event observable >> in any frame. Yeup >> What I'm puzzled about is the intermediate descriptions: in the rivet >> frame, a compressional wave travels up the shaft of the rivet until >> the plate hits the head. In the plate frame, a _dilational_ wave seems >> to travel down the rivet from the opposite direction until the foot of >> the rivet hits the backstop. How to reconcile these descriptions? You (Edward) are the one making them up. Perhaps you can explain what you mean by a dilation wave? > The velocity of a particle is also frame dependent. I don't see why > there is a need to reconcile events measured differently in different > frames.
From: Edward Green on 13 Jun 2010 10:53 On Jun 13, 12:19 am, "Inertial" <relativ...(a)rest.com> wrote: > "blackhead" <larryhar...(a)softhome.net> wrote in message > > news:5033df94-68e4-49c9-91b1-0e1f0197172a(a)w31g2000yqb.googlegroups.com... > > > On 13 June, 00:14, Edward Green <spamspamsp...(a)netzero.com> wrote: > >> I'm puzzled by some aspects of the bug and rivet paradox > > >>http://hyperphysics.phy-astr.gsu.edu/Hbase/Relativ/bugrivet.html > >> What I'm puzzled about is the intermediate descriptions: in the rivet > >> frame, a compressional wave travels up the shaft of the rivet until > >> the plate hits the head. In the plate frame, a _dilational_ wave seems > >> to travel down the rivet from the opposite direction until the foot of > >> the rivet hits the backstop. How to reconcile these descriptions? > > You (Edward) are the one making them up. Perhaps you can explain what you > mean by a dilation wave? In the frame of the plate, the impacting rivet is too short to hit the bottom initially. Hence we must see a region of dilating rivet traveling from the impact of the head until the impact of the foot. Part of this is the rivet coming to a stop in the plate's frame, hence assuming its normal length. However, the dilation must go beyond that, since by assumption the rivet at rest wrt the plate was too short to reach the bottom of the hole. What we have is a version of "no rigid bodies" in SR -- the rivet _must_ stretch.
From: Inertial on 13 Jun 2010 11:06 "Edward Green" <spamspamspam3(a)netzero.com> wrote in message news:9e346800-3ebf-4908-b4dd-85a888541ebe(a)h13g2000yqm.googlegroups.com... > On Jun 13, 12:19 am, "Inertial" <relativ...(a)rest.com> wrote: >> "blackhead" <larryhar...(a)softhome.net> wrote in message >> >> news:5033df94-68e4-49c9-91b1-0e1f0197172a(a)w31g2000yqb.googlegroups.com... >> >> > On 13 June, 00:14, Edward Green <spamspamsp...(a)netzero.com> wrote: >> >> I'm puzzled by some aspects of the bug and rivet paradox >> >> >>http://hyperphysics.phy-astr.gsu.edu/Hbase/Relativ/bugrivet.html > >> >> What I'm puzzled about is the intermediate descriptions: in the rivet >> >> frame, a compressional wave travels up the shaft of the rivet until >> >> the plate hits the head. In the plate frame, a _dilational_ wave seems >> >> to travel down the rivet from the opposite direction until the foot of >> >> the rivet hits the backstop. How to reconcile these descriptions? >> >> You (Edward) are the one making them up. Perhaps you can explain what >> you >> mean by a dilation wave? > > In the frame of the plate, the impacting rivet is too short to hit the > bottom initially. Hence we must see a region of dilating rivet > traveling from the impact of the head until the impact of the foot. Yeup .. the foot keeps going for a while after the head stops .. as the information from the head that it has stopped cannot travel to the foot faster than c > Part of this is the rivet coming to a stop in the plate's frame, hence > assuming its normal length. However, the dilation must go beyond that, > since by assumption the rivet at rest wrt the plate was too short to > reach the bottom of the hole. Is it? As I recall it fits perfectly when at rest, but due to length contraction the bug thinks (its a clever bug) that the rivet is now too short to reach it. But the rivet thinks (or at least some observer moving with it thinks) that the hold is contracted, and so the bug will surely die. > What we have is a version of "no rigid > bodies" in SR -- the rivet _must_ stretch. So why is that a problem?
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