# The puzzle of the bee and the train **URL:** \ **Category:** Factual Questions\ **Created:** [October 6, 2008, 4:55pm UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696 "2008-10-06T16:55:17Z")\ **Posts on this page:** 20\ **Page:** 5
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 10, 2008, 11:43pm UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/81 "2008-10-10T23:43:33Z")
> [@Pedro](#): > > Yeah, I don’t think so, since you also said this in post #40: Hey! You only quoted part of the post - omitting the important bits about non-rigidity and elastic coupling. ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [October 10, 2008, 11:56pm UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/82 "2008-10-10T23:56:10Z")
> [@Mangetout](#): > > Hey! You only quoted part of the post - omitting the important bits about non-rigidity and elastic coupling. You’re right, I apologize, I did not re-read what you wrote in post #40 carefully enough. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [October 11, 2008, 4:27am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/83 "2008-10-11T04:27:03Z")
> [@panamajack](#): > > How is this an oxymoron? If I have two blocks sliding past each other in opposite directions, are you claiming they aren’t really in contact, or not really travelling in opposite directions? You are quite right. I overstated. It is only silly if we are talking about the contact face of things moving toward or away from one another. ---
**Author:** ![scottie](https://avatars.discourse-cdn.com/v4/letter/s/cdc98d/32.png) [@scottie](https://boards.straightdope.com/u/scottie)\ **Post date:** [October 11, 2008, 9:32am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/84 "2008-10-11T09:32:42Z")
> [@Princhester](#): > > Frankly it has been answered upwards downwards and sideways, about six times over, using example after example after analogy. You just don’t get it and at this stage if I were you I’d consider resigning myself to the fact I wasn’t going to get it. There’s not much point in explaining it all to you yet again. You are obviously more easily pleased than I am. There have been many explanations of what is happening and the ways that calculations could be made but the central issue of stationary/non-stationary at the same time remain. ---
**Author:** ![scottie](https://avatars.discourse-cdn.com/v4/letter/s/cdc98d/32.png) [@scottie](https://boards.straightdope.com/u/scottie)\ **Post date:** [October 11, 2008, 9:42am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/85 "2008-10-11T09:42:08Z")
> [@RedSwinglineOne](#): > > I think it is worth noting that a lot of attention seems to be being paid to what happens “at speed zero”, or"when it passes through zero" as if it has some special significance, but it does not. > > Change the problem to a hovering bee is struck by a train traveling at 83 mph. What’s happening when the bee is traveling at 3mph? I like this answer. The problem is not markedly different but conceptually it doesn’t seem so difficult. It’s true I’m hung up on the zero point. I accept it doesn’t have any particular significance. I mught even be happy! Thanks. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [October 11, 2008, 10:16am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/86 "2008-10-11T10:16:30Z")
> [@scottie](#): > > You are obviously more easily pleased than I am. There have been many explanations of what is happening and the ways that calculations could be made but the central issue of stationary/non-stationary at the same time remain. Yes, it has. It was explained at posts 13, 17, 18, , 37, 54, 63, and not to mention most of the posts in the entire thread on the topic linked at post 23. The answer is simply flex. And when you say: > [@](#): > > It’s like claiming that the back of the train is going faster/slower than the front. the gulf between reality and your understanding becomes fully apparent. In fact, precisely this occurs all the time because there is a slight slack in the coupling of train carriages. When the engine starts moving at the front it can be a good few seconds before the carriages at the back start. When you grok this you may have a chance of understanding the answers you are being given to your question. And frankly unless you can explain precisely what it is about the trampoline or rubber sheet analogies you have been given that does not answer the “central issue” you are querying, I don’t see much point in continuing to try to explain. ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [October 11, 2008, 2:16pm UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/87 "2008-10-11T14:16:33Z")
> [@Princhester](#): > > And frankly unless you can explain precisely what it is about the trampoline or rubber sheet analogies you have been given that does not answer the “central issue” you are querying, I don’t see much point in continuing to try to explain. You are wrong. The analogy doesn’t hold up. The energy balance simply doesn’t pan out. Let me try another tack with you. Consider a system composed of two atoms, one Iron (Fe) and one Carbon (C). Fe is moving at +100km/h along an axis. C is moving at -1km/h along the same axis. They “collide inelastically” as you propose. The Fe atom is moving faster and is heavier than the C atom, therefore it has more energy. Then how can the C atom stop the Fe atom when reversing direction? Where does the missing energy come from? When you consider the case of a metal sheet against a bee ball it only makes this imbalance even more extreme. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [October 13, 2008, 3:58am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/88 "2008-10-13T03:58:55Z")
> [@Pedro](#): > > You are wrong. The analogy doesn’t hold up. The energy balance simply doesn’t pan out. > > Let me try another tack with you. Consider a system composed of two atoms, one Iron (Fe) and one Carbon (C). Fe is moving at +100km/h along an axis. C is moving at -1km/h along the same axis. They “collide inelastically” as you propose. The Fe atom is moving faster and is heavier than the C atom, therefore it has more energy. Then how can the C atom stop the Fe atom when reversing direction? Where does the missing energy come from? It won’t. The flex will occur within the inter atomic forces and the Fe atom will not stop. This is not incompatible with my position. > [@](#): > > When you consider the case of a metal sheet against a bee ball it only makes this imbalance even more extreme. Why so? All that is required is for there to be sufficient energy in the bee ball to balance off against so much of the metal sheet as is flexing and the extent of its flex. I don’t think our positions are actually in disagreement. You are just considering examples at the atomic level where the “flex” (in the form of inter atomic forces) can occur without stopping the atom as a whole, and I am considering a more general proposition. In the example of a baseball hitting a train with a trampoline on the front, what do you think the patch of the trampoline in contact with the most trainwards part of the baseball would be doing at the moment when the baseball is turned around and reverses direction? What speed would it be going? ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [October 13, 2008, 5:24am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/89 "2008-10-13T05:24:36Z")
Glad to see not everyone has abandoned this thread. > [@Princhester](#): > > It won’t. The flex will occur within the inter atomic forces and the Fe atom will not stop. This is not incompatible with my position. I wouldn’t call what I think you are describing as flex, since that’s a macroscopic concept, but so far so good. > [@](#): > > Why so? All that is required is for there to be sufficient energy in the bee ball to balance off against so much of the metal sheet as is flexing and the extent of its flex. But there isn’t sufficient energy to stop the metal contact patch, that’s my point exactly. > [@](#): > > I don’t think our positions are actually in disagreement. You are just considering examples at the atomic level where the “flex” (in the form of inter atomic forces) can occur without stopping the atom as a whole, and I am considering a more general proposition. If it doesn’t stop the atoms, it doesn’t stop the body composed of those same atoms. The bee compresses the metal. It doesn’t necessarily stop it at any point. Another analogy: Consider two magnets, with the same geometry, oriented to oppose each other, moving along a symmetry axis on a collision course. Magnet A is twice as massive and has twice the speed of magnet B. They oppose each other with equal in magnitude but opposite in sign forces. This force acts _at a distance_. Magnet B will stop and reverse direction, magnet A will only slow down, never actually stopping during the collision, which happens over a finite time and distance. Magnet A is the train contact patch and magnet B is the bee. I hope this analogy is clear, a diagram would help here but unfortunately I flunked my Physics ASCII drawing class. > [@](#): > > In the example of a baseball hitting a train with a trampoline on the front, what do you think the patch of the trampoline in contact with the most trainwards part of the baseball would be doing at the moment when the baseball is turned around and reverses direction? What speed would it be going? I’m certainly not claiming what you suggest can’t happen. The baseball in all likelihood will stop the trampoline at the contact point. But I don’t think the analogy holds for the bee-train collision. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [October 13, 2008, 7:27am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/90 "2008-10-13T07:27:13Z")
So we both accept that if the small thing is hard and heavy enough, and the big thing is soft and light enough, the latter will flex and a point on it will stop. I accept that if the small thing is soft and/or light enough and the big thing is heavy and hard enough, no part of the big thing will stop as the “flex” could be at a sub-atomic level. The difference between us is that I don’t know which case the bee hitting the train will fall into, and you think you do know that but have presented no quantified data that would enable you to reach the conclusion you have. ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [October 13, 2008, 1:34pm UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/91 "2008-10-13T13:34:39Z")
> [@Princhester](#): > > So we both accept that if the small thing is hard and heavy enough, and the big thing is soft and light enough, the latter will flex and a point on it will stop. I accept that if the small thing is soft and/or light enough and the big thing is heavy and hard enough, no part of the big thing will stop as the “flex” could be at a sub-atomic level. There is no “flex” at the sub-atomic level. And there are still some pretty wide gaps in your review, regarding conservation of momentum. > [@](#): > > The difference between us is that I don’t know which case the bee hitting the train will fall into, and you think you do know that but have presented no quantified data that would enable you to reach the conclusion you have. Now you’re just backpedaling and being disingenuous. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [October 14, 2008, 12:08am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/92 "2008-10-14T00:08:28Z")
> [@Pedro](#): > > There is no “flex” at the sub-atomic level. And there are still some pretty wide gaps in your review, regarding conservation of momentum. You’re just quibbling with terminology. I put “flex” in quotes. I know it’s not flex in any conventional sense but it is flex in the sense of something that allows two things to affect one another in a non-rigid way. As to the alleged gaps regarding conservation of momentum, you would have to say where you perceive them to be before I could comment. Until then, you are just indulging in reflexive naysaying. > [@](#): > > Now you’re just backpedaling and being disingenuous. Nonsense. You have said, not two posts ago, that in a particular small hard object, large flexy object collision, a part of the latter would stop. You have not supplied any data as to where the line would be between that and a collision where the latter would not stop, and everything would occur at the sub-atomic level. Yet you have stated categorically that the bee/train collision would occur via the latter. Provide some data or a cite, or accept you are speculating. ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [October 14, 2008, 12:58am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/93 "2008-10-14T00:58:46Z")
> [@Princhester](#): > > You’re just quibbling with terminology. I put “flex” in quotes. I know it’s not flex in any conventional sense but it is flex in the sense of something that allows two things to affect one another in a non-rigid way. You need a better word then. > [@](#): > > As to the alleged gaps regarding conservation of momentum, you would have to say where you perceive them to be before I could comment. Until then, you are just indulging in reflexive naysaying. I meant that you did not account for the kinetic energy of the bodies involved. Even a very light body (relatively to another) travelling very fast can carry a lot of energy, as I’m sure you know. > [@](#): > > Nonsense. You have said, not two posts ago, that in a particular small hard object, large flexy object collision, a part of the latter would stop. You have not supplied any data as to where the line would be between that and a collision where the latter would not stop, and everything would occur at the sub-atomic level. Yet you have stated categorically that the bee/train collision would occur via the latter. Provide some data or a cite, or accept you are speculating. I think I already laid out my arguments on this quite clearly. For instance, the magnet analogy and the atomic collision example. You agreed the Fe atom would not stop. I don’t see any reason to think a fast moving, massive solid network of Fe atoms and a small, slow carbon ball would behave any differently. Maybe you can shed some light on this? Beyond that, I don’t think I can be any clearer . The burden is on you to prove me wrong. Feel free to disagree, it was still a fruitful discussion for me. ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [October 14, 2008, 1:19am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/94 "2008-10-14T01:19:55Z")
It is also possible to have a situation where a trampoline colliding with a baseball ball would not actually stop, although the speed differential would have to be huge and the trampoline surface would stretch and slow down immensely, but never actually stopping. Of course, in a realistic scenario the trampoline fabric would tear much sooner than this. I know it’s not “cites and hard” data but there you go. ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [October 14, 2008, 1:42am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/95 "2008-10-14T01:42:23Z")
> [@Pedro](#): > > It is also possible to have a situation where a trampoline colliding with a baseball ball would not actually stop, although the speed differential would have to be huge and the trampoline surface would stretch and slow down immensely, but never actually stopping. Of course, in a realistic scenario the trampoline fabric would tear much sooner than this. Or better said, this scenario is completely unrealistic because a real trampoline could never attain the speeds required for this, and even if it could the baseball would probably explode upon impact. ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [October 14, 2008, 2:35am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/96 "2008-10-14T02:35:11Z")
Back of the envelope calculations say the trampoline speed would have to be approximately 100 times the speed of the baseball. It’s not as much as I thought… ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [October 14, 2008, 3:41am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/97 "2008-10-14T03:41:40Z")
> [@Pedro](#): > > I meant that you did not account for the kinetic energy of the bodies involved. Even a very light body (relatively to another) travelling very fast can carry a lot of energy, as I’m sure you know. You’ll have to explain what you see as the problem more coherently. What aspect of kinetic energy do you see as unaccounted for? Frankly, given that you have already accepted that at a sufficiently macro scale, and with a sufficient degree of elasticity involved, the contact area of the larger object will stop (ie we’re in agreement about this) why are you continuing to suggest there is a problem with the idea? > [@](#): > > I think I already laid out my arguments on this quite clearly. For instance, the magnet analogy and the atomic collision example. You did and I accept them. The only point I make is that if we are in agreement that at what we might call the extreme micro scale the more massive object would not stop, and if we are in agreement that at the extreme macro/trampoline scale it would, the only thing in issue is where the dividing line lies. Without quantified data, you simply can’t say. Which is why I don’t express a view on where the bee/train example lies. You do, so onus of proof is on you. > [@](#): > > You agreed the Fe atom would not stop. I don’t see any reason to think a fast moving, massive solid network of Fe atoms and a small, slow carbon ball would behave any differently. Maybe you can shed some light on this? Sure thing. When one atom collides with one other, (and assuming there is no chemical or nuclear reaction taking place) each object is indivisible, and the elasticity in the collision can only be through the interaction of fields. So the calculations are simple: one part of the Fe atom cannot be moving at a different speed to another part of it. Contrastingly, once we get to objects made of multiple atoms like, say, a train, one part of it can be moving at one speed and another part can move at different speed, while they are attached to one another, because materials can be flexible. Ain’t no such thing as a “solid” network of Fe atoms, in any absolute sense. ---
**Author:** ![Pedro](https://avatars.discourse-cdn.com/v4/letter/p/919ad9/32.png) [@Pedro](https://boards.straightdope.com/u/Pedro)\ **Post date:** [October 14, 2008, 5:32pm UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/98 "2008-10-14T17:32:51Z")
> [@Princhester](#): > > Without quantified data, you simply can’t say. Which is why I don’t express a view on where the bee/train example lies. You do, so onus of proof is on you. You did, here: > [@Princhester](#): > > At the time the stopped bee is in contact with an area at the front of the train, that area is also stopped because it is flexing microscopically backwards compared to the rest of the train. And again here: > [@Princhester](#): > > Any way you cut it, Pedro, if the bee passes through zero and is in contact with a part of the train while doing so, then that part of the train must also pass through zero. Otherwise you are talking about two things being in contact while not moving at the same speed, which (a) is clearly an oxymoron and (b) means that at the moment the bee is passing through zero it has nothing to accelerate it, since it is not in contact with anything, which means that it wouldn’t be passing through zero, which it is. Moving on: [QUOTE=Princhester] Sure thing. When one atom collides with one other, (and assuming there is no chemical or nuclear reaction taking place) each object is indivisible, and the elasticity in the collision can only be through the interaction of fields. So the calculations are simple: one part of the Fe atom cannot be moving at a different speed to another part of it. Contrastingly, once we get to objects made of multiple atoms like, say, a train, one part of it can be moving at one speed and another part can move at different speed, while they are attached to one another, because materials can be flexible. Ain’t no such thing as a “solid” network of Fe atoms, in any absolute sense. [/QUOTE] Of course. But seeing as every Fe atom pushes or collides with the surrounding outermost atoms, I maintain there is not enough energy in the bee to stop the train surface, relative to an external observer. Instead there will be a compression wave squashing the bee. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [October 16, 2008, 10:20am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/99 "2008-10-16T10:20:04Z")
You’re right, I see. I accept your correction that I adjusted my position to be a synthesis of both our positions. However, the fact is that right now you are saying that it is one thing and not the other, and you have no quantified data. ISTM that it may be that as we move more and more towards the macro scale, the contact point on the larger object gets closer and closer to being stopped, but whether the surface actually stops depends on the atomic makeup of each object. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [October 16, 2008, 10:23am UTC](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696/100 "2008-10-16T10:23:08Z")
Or could it perhaps depend upon the harmonics of the thing struck? When the bee hits it’s going to cause the front of the train to reverberate. What is going to affect the speed of vibration? Is that speed going to be higher or lower than the speed of the train? [Previous page](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696.md?page=4) [Next page](https://boards.straightdope.com/t/the-puzzle-of-the-bee-and-the-train/466696.md?page=6)