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Huygens' Clock Puzzle Solved 191

Posted by Hemos from the tick-tock-tick-tick-tock dept.
PhotoGuy writes "Okay, I haven't heard of this puzzle either until now, but it sounds like a fascinating phenomenon. According to this article:Huygens had two clocks side by side and he found that even when they began out of sync, they soon got into a rhythm where the pendulum on one moved as if it were a mirror image of the other.The article is pretty light on the explanation, noting only the conditions required (small relative mass of the pendulums [pendula?], relatively close speed of the clocks), and not really addressing the physics behind it. " There's a great site at Georgia Tech that explains the puzzle in more detail.
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Huygens' Clock Puzzle Solved More

Huygens' Clock Puzzle Solved

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  • odds (Score:3, Interesting)

    by yawnmoth ( 534382 ) on Thursday February 21, 2002 @04:47AM (#3043293)
    [quote]The combined mass of the pendulums has to be very small compared to the combined mass of the entire clock assembly and frame - this was where Huygens was lucky. [/quote] i'm not sure where non linear dynamics and chaos theory come into this, but ah well... i probably wouldn't understand it, anyways. so... that which intrigues man has gone from undiscovered land masses, to redisocvered lost cities, and now to ancient riddles. i wonder what we're going to do for intrigue once we solve all these ancient riddles...

  • the article from wired about it (Score:5, Informative)

    by itsnotme ( 20905 ) on Thursday February 21, 2002 @04:47AM (#3043296) Homepage
    The GA tech column had an link to a picture of the wired article about it, I dug into Wired and found the text so it's more readable.. the link is: http://www.wired.com/wired/archive/9.03/eword.html ?pg=6

  • A better article... (Score:5, Informative)

    by LordSah ( 185088 ) on Thursday February 21, 2002 @04:47AM (#3043299)
    http://www.sciencenews.org/20001007/mathtrek.asp [sciencenews.org]

  • Antiphase (Score:3, Interesting)

    by BlueUnderwear ( 73957 ) on Thursday February 21, 2002 @04:52AM (#3043307)
    The Georgia Tech article mentions that clocks actually get into antiphase synchronization (when one pendulum swings to the right, the other goes to the left, and vice-versa).

    Strangely enough, it didn't occur to them to test what happens if they put three clocks side by side... Antiphase synchronization seems somewhat hard with an odd number of clocks...

    • Re:Antiphase (Score:5, Insightful)

      by jonnythan ( 79727 ) on Thursday February 21, 2002 @05:08AM (#3043333)
      Not so. The three would each be off by 1/3 of a period.

      Just like three phase power... three sine waves 120 degrees apart. Sum them and you have a constant 0.

      I've no idea if that would actually happen in that setup, but my guess would be that yes, they would cancel each other out in total antiphase this way.

      • Re:Antiphase (Score:3, Interesting)

        by God! Awful ( 181117 )
        Very likely so.

        There are two key principles at work here: Newton's laws (every action has an equal and opposite reaction), and equilibrium (if you disturb one of the pendulums it will tend to act in such a way as to restore the equilibrium).

        If we look at the 2 pendulum example, when the pendulums are swinging 180 degs out of phase, there is 0 net force on the system. Let's say you apply an impulse which brakes pendulum A while it is on the upswing. This will momentarily slow down pendulum A and cause it to lead pendulum B. When pendulum A reaches its would-be apex, pendulum B will exert a force on it, causing A to go higher and simultaneously lag slightly. Thus, equilibrium is restored.

        In the 3 pendulum situation, the momentums again cancel each other out. At one point, pendulum A is at the bottom going right, pendulum B is near the top right going down (left), and pendulum C is near the top left going up (left). Pendulums B & C exert equal and opposite forces at this point, so the net force on A is 0. Say we brake B slightly here. Normally, when B reaches its apex, the forces due to A and C cancel each other out. But B will reach its apex earlier; therefore, A-C will exert a force on it, causing it to go higher as before.

        This suggests to me that equilibrium will also be restored in the 3 pendulum case. Of course, I am not a qualified physisist, so I might just be ranting here...

        -a

    • Hoax (Score:1, Interesting)

      by inKubus ( 199753 )
      I would say the simple solution is gravity, plain and simple.

      You have two masses moving, in essence, side to side (horizontally).

      X

      The masses are equal, but not perfectly in sync. It's pretty impossible to get anything perfectly in sync. So basically, sooner or later, they will both reach the center point X at the same time. When they do, the gravitational attraction between the two masses is at it's highest. When the pendulums begin to move apart again, they are affected by an equal force resisting them moving apart. Regardless of their acceleration away from each other, they will from this point forward always come to the center point at the same time, because that is where they "want" to be.

      If you want to wax intellectually on the subject, we can take a look at the clocks themselves.



      As each pendulum swings, it imparts a torque on each clock. When the pendulums meet in the middle as I've described above, the torque on each clock is exactly equal and opposite also. Assuming the clocks are equal in mass they will fall back like little pendulums themselves, but at the same rate.
      So what we have, basically, is gravity multiplying itself harmonically. Fascinating.
      Bah.

      • Re:Hoax (Score:2, Funny)

        by Sarcazmo ( 555312 )
        gravitational attraction between objects that weigh a couple ounces? You have to be kidding.

      • Re:Hoax (Score:4, Insightful)

        by InfinIT ( 557535 ) on Thursday February 21, 2002 @09:36AM (#3044053)
        Not really, Although you have a valid point, the article specifically states that the effect only worked on smaller weighted pendulums - larger ones would have a stronger gravitational effect. On top of this, if both pendulums were started in the same direction, then they would not be moving away from each other and thus the gravitational effects on each other would be unchanging. Thus gravitational effect would have no bearing at all. In the article at Science News (http://www.sciencenews.org/20001007/mathtrek.asp) they specifically mention that the pendulums were started in opposite directions, and also in the same direction.

  • Mainly luck? (Score:3, Interesting)

    by bagel2ooo ( 106312 ) on Thursday February 21, 2002 @04:52AM (#3043310)
    When I was looking at this I was expecting something filled with tons of wizzbang scientific explainations. Sad that something that has stumped people since the 17th century turns out to be primarily luck.

    • Re:Mainly luck? (Score:4, Interesting)

      by LordSah ( 185088 ) on Thursday February 21, 2002 @05:05AM (#3043328)
      It seems that the main reason this happens is that the synchronus movement causes less vibration in the system as a whole, and therefore conserves more energy. A path-of-least-resistance sort of thing.

      Perhaps there's a physics major out there who could explain better...

      • Re:Mainly luck? (Score:5, Interesting)

        by lkeagle ( 519176 ) on Thursday February 21, 2002 @05:39AM (#3043408) Homepage
        It's a very difficult problem to model. It involves two pendulums (both of which, despite what many of your freshmen physics professors told you, are nonlinear oscillators), and a coupling mass.

        The coupled oscillators are difficult enough to model by themselves. I wrote a paper once on coupled physical pendulums. After quite a bit of very complicated physics involving Hamiltonians and Lagrangians and other silly names, I managed to derive an equation that describes the motion of the two pendulums in terms of the 'normal modes' of oscillation (these are closely related to the 'in phase' and 'out of phase' vibrations). Needless to say, the equation took up a good 3 lines in the report. I should have just put it in an appendix.

        Now if you add a coupling mass between them, you're talking about an even MORE complicated problem, because the inertia of the coupling platform affects the resonance of the pendulums. It's very much like an inductor in electronics. It doesn't allow energy transfer to happen directly through the two pendulums, because a pendulum has to push the whole mass in order to get energy over to the other pendulum. I would imagine, just through experience in nonlinear systems, that increasing and decreasing this mass will have yet more nonlinear effects on the system (such as the complete stopping of one pendulum, although the article was unclear as to whether this was a complete halt, or just momentary).

        You'll find very little chaos in this system, unless the pendulums are started at a very large height. Also, like most undergraduate physics, this analysis completely ignores the effects of friction, which is where the only true energy 'loss' would happen.

        Mod this down for overkill,

        ~Loren

        • Re:Mainly luck? (Score:1, Flamebait)

          by ishark ( 245915 )
          It's a very difficult problem to model. It involves two pendulums (both of which, despite what many of your freshmen physics professors told you, are nonlinear oscillators), and a coupling mass.

          I'm not familiar with this particular system, but are you sure you need to consider nonlinearities to obtain the synchronization? Isn't some k(x1-x2) enough to deal with it?
          I don't have the time now to hack together a perl script to simulate the system, I'll try later...

          • No nonlinear behaviour out of a linear System (Score:5, Interesting)

            by gotan ( 60103 ) on Thursday February 21, 2002 @07:22AM (#3043631) Homepage
            No, simple linear dynamics won't help you (and if they work out with your perl-script, then probably because of nonlinearities creeping in due to rounding). That is, because you can only get linear behaviour out of a linear system. That means a linear system can be described by a matrix, and the eigenvalues of that matrix will give you the frequencies of oscillations that may happen (given the System oscillates about a stable state). If you couple linear systems in a linear fashion (like with a force k(x1-x2) as you suppose) you only get a bigger linear system, with more oscillation modes.

            In a purely linear system all these modes of oscillation are independent of each other. But the clocks manage to get from one mode of oscillation into another. This can only happen, if energy is somehow transferred between the modes, and to get that you need a (nonlinear, or you get just another linear system with slightly different modes) coupling between the modes.

            Linear Systems are, in a sense, boring, once you have worked out all the coupling constants, put them in a matrix and found it's eigenvalues you know all about it (for large enough systems, say a crystall with 10^23 Atoms that can be quite a feat and can get you some interesting results nevertheless) and can predict it into all eternity. The interesting stuff happens when nonlinearities creep in.

            You could describe our solar system in a linear manner, and you will learn much about it by that, mainly that the planets orbit about the sun and are themselves orbited by moons. But if you want to know why some orbits more stable than others, for example why there are gaps in the saturn rings for orbits in sync (with w being a multiple of the W of the moon) with the moons, you have to look into the nonlinearities.

            --
      • But systems don't tend toward conserving energy. On the contrary, they tend toward expending it, in order to end up in a lower-energy state.

        The way this all makes sense to me is to consider that any movement besides antiphase vibration causes the common support to move very slightly, which damps that vibration. Thus, all vibration besides antiphase is damped, and after a long time, all that "remains" is the antiphase vibration.

        The continual amplification caused by the clock spring "normalizes" whatever tiny antiphase component existed originally or develops later, until finally the pendulums (pendula?) are swinging in antiphase at full amplitude.

      • Re:Mainly luck? (Score:2, Informative)

        by jstott ( 212041 )
        t seems that the main reason this happens is that the synchronus movement causes less vibration in the system as a whole, and therefore conserves more energy. A path-of-least-resistance sort of thing.

        Perhaps there's a physics major out there who could explain better...

        That's basically it. The proper term is mode-locking. It's also the reason why one side of the moon always faces the earth and why there's a 3/2 ratio in the time of the orbits of Uranus to Neptune. You can also make some really cool high-power lasers if you mode-lock the period to the cavity length (Ti:Sapphires are the most common).

        -JS

    • The following one paragraph anecdotal explanation (with no equations) of why two clocks might be more stable in anti-resonance.

      If we think of dynamic systems in terms of energy states, more energy is bad less energy is good. For example, a ball rolls to the bottom of a hill and stays there. The solution to the clock riddle falls out of this simple principle. When the clocks are any state but anti-resonance the frame that connects them would be caused to move and thus damp the clocks into the direction of anti-resonance (the ball rolls down the hill). When the clocks are in anti-resonance the motion of the pendulums cancel the motion in the connecting frame and thus the damping stops (the ball is at the bottom of the hill)

      In a similar vein, my wife and I have the same problem. When we lie in bed at night, I have to wiggle my feet to get to sleep (commonly known as restless leg syndrome). If I keep my feet in anti-resonance, the bed moves very little and my wife can sleep, however, if my feet wiggle in phase (resonance) then my wife wakes up and does mean things to me (think of this as a damping force that causes the system to move into anti-resonance). I am sure if we spend enough time thinking about this solution we can base a whole philosophy (and maybe a new wave religion on it) but I will leave that to someone else and get back to work.

    • I was expecting any explanation from the article.

      Instead, they just tell us this puzzle has been unsolved since C17, and now it's solved.

      Would someone mind telling us, now that it's solved, WHY it happens?

      It's like the editor forgot to publish page 2.

  • Ok. Now what? (Score:4, Insightful)

    by Jhon ( 241832 ) on Thursday February 21, 2002 @05:07AM (#3043331) Homepage Journal
    I'm interested to see if this may lead to a better understanding of how harmonics works with relation to high-rise buildings. Particularly in earthquake country. (see this [fema.gov])

    We've got buildings that can withstand strong quakes -- but not necessarily those of long duration. I'll bet a shiny new penny that this reseach may be insightful in this field.

    -jhon
    • If you had two free-standing buildings, that were light, next to each other, and have very similar fundamental frequencies (mass, interial moment, ...), then they could potentially sway in antiphase. Methinks, is this a microgravity effect? F = -G*m1*m2/r^2
  • >"Classical physics still has things to teach us,"

    Did anyone think otherwise?

  • Periods (Score:2, Troll)

    by seanadams.com ( 463190 )
    My g/f in high school used to start her period on exactly the same day as all the other girls on her soccer team - amazing. I've also heard that girls often have their periods in sync with their mothers'. Has anyone formally attempted to relate this to the pendulum phenomenon?

    • Re:Periods (Score:4, Informative)

      by ender81b ( 520454 ) <wdinger@@@gmail...com> on Thursday February 21, 2002 @05:29AM (#3043382) Homepage Journal
      That's called the Harem effect (or something like that). Basically you get any number of women, greater than 1, put them into close contact with each other and they all have their period at the (nearly) same time. Well documented phenomeon(sp?).

      Harem, because a man could impregnate his entire Harem in a single day since they all became fertile on the same day.
      • Yeah, you try that, you Geek!

        Depending on the number of women of course, but if you did try it, I wonder if those kids will ever meet their father alive, or in a wheelchair.

        Dave
        • if you did try it, I wonder if those kids will ever meet their father alive, or in a wheelchair.

          Reminds me of something by Wes Borg [deadtroll.com]..

          "How come condoms only come in packs of 5 or 6, but women only come in packs of 2 or 3?"

          "I saw a pack of 24 condoms the other day! I personally think that a pack of 24 condoms should come with free Gatoraid and crutches."

      • Re:Periods (Score:5, Funny)

        by sql*kitten ( 1359 ) on Thursday February 21, 2002 @06:18AM (#3043468)
        Harem, because a man could impregnate his entire Harem in a single day since they all became fertile on the same day.

        More likely because a harem would be an environment in which many women lived together without much contact with the outside world.

        I mean, some of these sheiks were reputed to have dozens of women in their harems. No way he could impregate them all on the same day , at least not with the technology that existed at the time.

        Nowadays, for that sort of thing, we have Cowboy Neal...
        • I'm fairly sure that their attitude, at least mine would be, So Many Women, So Little Time.

          =)
        • He'd be very tired but he could get a fairly high number of them. I doubt Solomon would have been up to the task with his 1000 women, but a dozen is probably within reach. "Dozens" is probably out of reach.

          Of course he could send in a substitute impregnator (they did have that technology back then) but that kinda defeats the purpose of having a harem.

        • Re:Periods (Score:4, Funny)

          by Gannoc ( 210256 ) on Thursday February 21, 2002 @12:05PM (#3044869)
          I mean, some of these sheiks were reputed to have dozens of women in their harems. No way he could impregate them all on the same day , at least not with the technology that existed at the time.

          Sounds like a great premise for a Fox reality game show.

        • No way he could impregate them all on the same day , at least not with the technology that existed at the time.
          Just when did they invent the turkey baster?
      • Harem, because a man could impregnate his entire Harem in a single day since they all became fertile on the same day.

        The logical solution to this is to either mutilate yourself or mutilate every single woman,
        we all know which one that's commonly used.

      • Re:Periods (Score:2, Informative)

        by chad_r ( 79875 )
        Is it true the menstrual cycles of women living together tend to synchronize? [straightdope.com]

        ... This amazing phenomenon was first described in 1971 by researcher Martha McClintock, now with the University of Chicago. Having asked around a bit, I'd say it's common knowledge among women, but I'll bet not one male in 50 has ever heard of it. Women do have their little secrets....

        ...Later research has suggested that synchrony is caused by some sort of scent cue, or pheromone.

        Scientists at the Sonoma State Hospital Brain Behavior Research Center in California identified several women who were believed to be menstrual pacesetters--they made other women conform to their cycles.

        The scientists placed cotton pads under the dominant women's arms for a day, and then wiped the pads on the upper lips of five female subjects three times a week. (One wonders how much the subjects got paid for this.)

        Within five months, four of the recipients were menstruating at the same time as their donors.

        Interestingly, men also have an effect on women's menstrual cycles--and not just because they make women pregnant. Women who associate with males frequently find that their periods become shorter and more regular....

      • That's called the Harem effect (or something like that). Basically you get any number of women, greater than 1, put them into close contact with each other and they all have their period at the (nearly) same time. Well documented phenomeon(sp?)

        It MAY be related to the fact that roughly half the estrogen in the body is produced by cells in the lungs. (It's the particular cell type that sometimes becomes cancerous, which is why lung cancers often have effects on secondary sexual characteristics, such as breast enlargement.)

        Now I don't KNOW of any proven causual relationship. But the location of these cells in the lungs makes me wonder if they might be acting as chemosensors, with their estrogen output modulated by some airborne signaling chemical. This in turn could be responsible for all sorts of interesting and advantageous effects (both in humans and other animals), such as ovulation and/or coming into heat in response to proximity to a fertile male.

        One such effect might be synchronization of periods of women in long-term proximity, via estrogen release by these cells in response to a signaling pheromone emitted by the other women. Synchronized periods would help maintain pair bonding by reducing the temptation for a man to mate with other women when his usual mate was having a period and the other women were not.

    • Re:Periods (Score:2, Informative)

      by Tha_Zanthrax ( 521419 )
      What you're explaining is pretty common for women who spend a lot of time together. It's being caused by pheromones and why it happens... I forget.

      Unless someone discovers clocks with pheremones these things aren't related.

    • No similarity (Score:2, Informative)

      by Jetson ( 176002 )
      The synchronizing of the female reproductive cycle is thought to be the result of pheremones. I suppose it's some prehistoric competitive thing that ensures the male never has to resort to the less dominant females.

      That has nothing to do with pendulums. The key point of the phenomenon is that the two clocks must be on a base which is wobbly enough to transmit the "equal and opposite reaction" of the pendulum from one clock to the other while being strong enough to prevent the pendulum from swinging the clock.

      • Re:No similarity (Score:3, Insightful)

        by ishark ( 245915 )
        That has nothing to do with pendulums.

        It seems to me that it's very much the same thing. In both cases you have oscillators with periods very similar to each other linked by very weak coupling.
        The interesting things are that this coupling, even if it's very weak, can influence the system and bring up synchronization and that depending on what's up you can have locking on an in-phase state or an anti-phase state.
        The same kind of things happens in a lot of other systems, like for example the coupled lasers I have here.... (in-phase and anti-phase in this case appear depending on the sign of the coupling coefficient).
    • A related pheromonal phenomenon is the Lee-Boot effect. When groups of female mice are housed together their estrous cycles slow down and eventually stop until they are exposed to the scent of a male mouse or his urine.
    • I've read reports of the women in our local zoo here who have their periods synchronized with those of the female apes they nurse.

      Dave

      • They NURSE?!?!?! (Score:1, Funny)

        by Anonymous Coward
        women in our local zoo here who have their periods synchronized with those of the female apes they nurse.

        Somehow, I doubt that the women there actually nurse the apes. Even if human milk was actually good for apes, I'd think they would use breast pumps, wouldn't they?

        Of course, if I'm wrong, I'm sure the videos would sell well on those bestiality porno web sites :o)

    • Re:Periods (Score:1, Funny)

      by ez76 ( 322080 )

      My g/f in high school used to start her period on exactly the same day as all the other girls on her soccer team - amazing
      This is actually how the first period of a soccer game usually begins. Moreover, all the girls usually start at the same time. Something with pheromones ...
    • This is known as the McClintock Effect. It has nothing to do with mice and everything to do with women living together in college dormitories (how the effect was discovered). Here's an interesting looking paper on it: Pheromones: The Smell of Beauty [colorado.edu] on it from 1997.
    • This is fascinating... why? Millions of people show up at work at the same time every day. That is a conscious, voluntary act. But why is it any more surprising when an unconscious, involuntary act is involved?

  • Awhile ago... (Score:2)

    by Anonymous Coward
    ...I heard that the reason the clocks go into synch is because they are connected to the same table. Now, when a pendulum stops swinging, it's momentarily "suspended" in the same way that a baseball is when it reaches its zenith just before it comes crashing down on you after you've thrown it directly up. At this point of 'suspension', there is /no/ force between the weight at the end of the pendulum and the rest of the pendulum. It's as if the weight weren't there at all. At all /other/ points, however (especially when the pendulum reaches its fastest point at the nadir of its swing), there obviously /is/ a force between the weight and the arm swinging it, if only because of the fact that the weight is moving (not momentarily suspended) and movement causes friction. This 'friction' manifests itself as vibrations between the arm of the pendulum and whatever it's connected with (even if it's just a nail that a rope is swinging from with a weight at the end of). Now let's say that because the whole frame isn't designed to take advantage of vibrations or treat them any special way, the net effect is just "random"...
    Now, then, we see why the two pendula come into synch: except for the points where the pendula are momentarily 'at rest', there is always a slight random noise they're giving out. This noise is greatest when their momentum is greatest, and, by coincidence, a pendulum is least able to be disturbed when its momentum is greatest.
    (Okay, old physics puzzle: disregarding air resistance, how will two pennies behave with respect to each other if you throw down one, and then the second a tenth of a second later? Answer: they will grow farther and farther apart, and the speed of the first will at one point be more than a million miles per second faster than the speed of the second!)
    So, to recap:
    If a and b are in synch, then when b is moving fastest it's producing the most disturbance, but this disturbs a the least because its large momentum means that this change is minor for it. (And vice versa). At every other point, however, the disturbance tends to disturb a /more/: extreme example: if a comes to a stop just as b reaches its greatest momentum (nadir), then a has the greatest disturbance at it just when it counts the most. When they are in synch, however, a has the greatest disturbance at it just when it counts the last. Therefore, after a while the system will "settle" on disturbing itself only when it doesn't matter. (Since at all other times, it's an extremely unstable system, assuming that because of weird friction, etc, the 'noise' of the vibrations is more or less random.)
    Hope this helps.
    Anonymous J. Coward.
    Professor of Entymology,
    University of Timbuktoo.
    • I really hate to cause anything remotely flame-related, but this is one of the poorest examples of good physics and reasoning I've come across...

      I'm not gonna say that it's wrong (ahem...), but without examining resonance and vibrational coupling, you have no way to explain your 'noise'. Energy will be transferred whether something is at rest or not... You can't stop it.

      ~Loren
    • This (non) explaination has two solutions; the pendulums can swing in phase or in anti-phase. The observation says they always swing in anti-phase.

      Stick to the Etymology/Entomology, whichever it is.
    • (Okay, old physics puzzle: disregarding air resistance, how will two pennies behave with respect to each other if you throw down one, and then the second a tenth of a second later? Answer: they will grow farther and farther apart, and the speed of the first will at one point be more than a million miles per second faster than the speed of the second!)

      A million miles per second? That's some gravity well. What are we dropping these into, a neutron star?

      Or are these pennies of the Elbonian currency, the tachyon?
    • Two pennies moving away from each other at the speed of light would only account for 372000 miles per second. How the heck do you get "more than a million miles per second"? OHIBT?

  • trivial? (Score:3, Interesting)

    by brad3378 ( 155304 ) on Thursday February 21, 2002 @05:27AM (#3043378)
    From the Article:

    &gt
    As Huygens surmised, the platform motion is the culprit: if we prevent the platform from moving, there is no synchronization at all

    Can you believe it took this long to solve this problem? I admit I'm sceptical. Am I missing something?
    Here's how I interpret the phenomenon:

    Imagine two pendulums hanging side by side (on a rocking boat (I tried to make ASCii art, but the lameness filters don't like whitespace) Align the pendulums so that they swing in the direction of the boat rocking side to side.
    Pull the pendulums apart and release simultaneously (assume they don't collide).
    Initially they are 180 degrees out of phase, but as the boat starts rocking, its like giving one an extra push (in phase), while the other (out of phase) pendulum a tug to shift its sinewave in the opposite direction. Eventually both pendulums will have the same phase shift and will be affected by the rocking boat equally.

    A slightly more complicated example could include two children on a swingset put into phase by giving each a strategically timed push or by loosely comparing it to the harmonics that caused the destruction of the Tacoma Narrows Bridge in those old film clips.

    Sounds more like vibes 101 problem than a 336 year old unsolved problem.
    Am I overlooking something?

    • Re:trivial? (Score:2, Informative)

      by Hammerself ( 560585 )
      In this (Huygens') case they start out in phase and move to 180 degrees out of phase.
    • I seem to recall from my childhood that it took effort to stay in-phase with someone swinging next to you, and if you both just swung normally you'd end up in anti-phase, even if you started together. This would be related, I assume?

  • Mickey Hart called it "Entrainment" (Score:3, Interesting)

    by Inthewire ( 521207 ) on Thursday February 21, 2002 @05:28AM (#3043379)
    The first time I heard of this was in a book called _Drumming at the Edge of Magic_, written by former Greatful Dead drummer Mickey Hart.
    He was discussing the pervasiveness of rhythm, and used this as an example.

    Of course, he didn't try to explain the science, and I wondered why at the time.

  • Everything was already discovered... (Score:3, Funny)

    by Kopretinka ( 97408 ) on Thursday February 21, 2002 @05:29AM (#3043380) Homepage
    It seems that Huygens' was the first observation of a phenomenon known now at the subatomic scale as particle coupling. The youngsters (Hawking et al) can still learn a few tricks from the guys of the past. 8-)
    • "These whippersnappers don't know how easy they have it. In my day we didn't have your fancy 'SQUIDS' or 'Oscilloscopes' or even ballpoint pens. We had gears and springs and lumps of metal. We had to invent clocks and build them ourselves, by hand. We would sit all day and watch our clocks. And we liked it! We were darn fools and didn't know any better." -Grumpy Old Physicist

  • grenwich, in london (Score:5, Interesting)

    by gol64738 ( 225528 ) on Thursday February 21, 2002 @05:58AM (#3043437)
    If anyone is interested in accuracy in time keeping, a trip to the Royal Observatory in Grenwich is a must for you. You can see Huygens' parabolic pendulum located there.

    Get to know about John Harrison, who made the first 'accurate' timekeeper, for use at sea to measure longitude. See Harrisons first accurate time peices of the world, H1 thru H4, where H1-H3 still ticks today.

    A must is to stand on the prime meridian of the world, which represents 0 degree longitude, also located there. At night, a green laser can be seen streaking across the sky marking the zero parallel.

    Check out the Royal Observatory [nmm.ac.uk], you won't regret it!
    • Hey, we've got a Royal Observatory employee on Slashdot. Cool :)
    • The cable channel A&E is running part 2 of
      Longitude, a movie about Harrison and his
      clocks, tonight, I believe. I saw part 1 last
      week and it was quite good. Probably they'll
      rerun it in the middle of the night sometime
      soon.
    • > Get to know about John Harrison, who made the first 'accurate'
      > timekeeper, for use at sea to measure longitude.

      Nova [pbs.org] has a great show about John Harrison and the creation of his timekeeper, called Longitude [pbs.org].
    • I've just finished reading "Longitude, The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time" by Dava Sobel - a history of John Harrison vs. the Board of Longitude and the development of the chronometer. Recommended to anyone with even the slightest interest in clocks or navigation.

      It was strange to read in the linked article (Georgia) that Huygens' clocks "contained heavy lead weights in order to keep them upright in stormy seas" - this muct be a mistake. Clocks with pendulums are absolutely useless in any kind of sea, even a calm one, hence Harrison's search for the chronometer resistant to motion and to changes in temperature and humiduty.

      One part I really liked is that after Greenwich was declared the Prime Meridian in 1884 the French, for 27 years, referred to GMT as "Paris Mean Time, retarded by nine minutes twenty-one seconds".
      • That is an excellant book.. I believe there was a /. review a while back. I recommend it for anyone.. its a fairly short book and is written well enough to be easily understood.
        • I've read the smaller paperback, but when i was in Grenwich, i purchased the large, illustrated version. The illustriations are amazing, and I recommend you check out this one.
    • Unfortunately, the Royal Observatory has gone a little soft in the science in the attempt to attract tourists. It's not quite as bad as Disney, but it's definitely enough that people who actually care about this stuff will go quietly mad. (Disclaimer: the following comments are based on reports I've seen in various locations over the past few years - it's possible they finally got their act together.)

      The most obvious to most people is the fact that a GPS shows that the PM is marked by an unlabeled garbage can (read: ignored) while the PM marker is a substantial distance off - as much as 100m?.

      There's actually an easy and fascinating explanation. Geographical positions were originally determined by astronomy, and this implicitly took into account the actual complex shape of the earth. Most slashdot readers know about the equatorial bulge, but there are other bumps and valleys as well. But modern positioning uses GPS and a simplified model of the earth's shape, and the coordinates do not match exactly. Minimizing the differences worldwide required a sizeable jump in the London area.

      This then brings up the difference between astronomical time and atomic time, how GMT tracks the former and UTC tracks the latter, and the need for leap seasons.

      I think it's reasonable to expect anyone who knows enough science to visit the RO would find this interesting, but the RO apparently doesn't. Most people think the positioning of a garbage can on the true PM was an accident, I'm not so sure.

      Even more bizarre was their behavior around January 1st, 2000. It wasn't Y2K until it was Y2K in London. Except it was. Except it wasn't. I don't think anyone ever figured out what their position was, except that all celebrations should somehow refer to them. (It got so bad I half expected to see a claim that the RO patented Y2K.)

      Ironically, I never heard of any reference to the reason why this time zone was first among equals - the fact that UTC is widely used in computers, telecommunications, etc. Half of the world (by definitition!) may have been in 2000 by the time it hit midnight in London, but much of the technology of the world would turn over at that time. That's why I was glued to the TV at 5 pm local time, with CNN on one TV and BBC America on another.

      If you have a chance to visit the RO, take it. But think of it as "Royal Observatory World," the theme park.
    • Get to know about John Harrison, who made the first 'accurate' timekeeper, for use at sea to measure longitude. See Harrisons first accurate time peices of the world, H1 thru H4, where H1-H3 still ticks today.

      Leave me out of this!

  • vibration transmission (Score:1, Insightful)

    by Anonymous Coward
    isn't this analogous to the playground swingset, where when you swing on one, the other moves, due to the vibrations being transmitted thru the swing overhang?

    uh news?

    i noticed that shit when i was like 4.

  • That's a weird clock you have:)
  • The most common form of this problem is two pendulums hanging from a string. Stretch a string, the tightness is not important. hang two strings from the first string. put weights on the bottoms of the hanging string. swing the pendula across the axis of the first string. voila! coupled pendulums. It's a standard problem in hamiltonian dynamics, and taught in most university physics courses.

    another example is a pendulum with one or more hinges in the middle of a stiff rod.
    • Nobody has mentioned this, but it seems to me that out of phase dual-pendulums connected by to the same structure have existed long before Huygens' clock: The human body with two arms!

      Each of your arms strongly tends to swing out of sync with the other. If your arms were very tiny, this wouldn't happen and if they were gigantic, it wouldn't happen either. This was observed and no doubt pondered thousands of years before Huygens' did the same thing with clocks.

  • This whacky guy observed and measured the effect [bmumford.com] in his own clocks.

    BugBear
  • In a piano, some of the keys strike a pair (or three) strings when struck. Piano tuners tune each of the strings independently, but also realize that one string affects its mate. Even if they are tuned just a titch off from one another, they will try to sycnh up. Instead of seeking to tune the pair perfectly together, detuning one from the other very slightly will affect the loger-term 'envelope" of the note.

  • Massive Huygens entrainment. (Score:5, Informative)

    by Richard Kirk ( 535523 ) on Thursday February 21, 2002 @07:59AM (#3043721)
    I one had a posting from an old steam train worker on Africa somwhere. They used to have pairs of back-to-back steam engines for pulling heavy trains. The drive wheels used to have a random scatter in the diameter, and people in the engine shed used to try and match up sets of driving wheels with the same diameter, because that made the enginges 'run more smoothly'. From his account, it seems that on long, straight sections of track, the two engines would lock into step, but only if the wheels were a near match on both engines.

    You get it with piano strings too. Where two or more are tuned to the same note. The delta in tuning has an important on the sustain-decay profile of the notes.

    Huygens figured out the general principle. If you have two things that are matched in frequency, and capable of influencing each other, then any influence, however tiny, will eventually drag them into some preferred phase relationship. If there is some difference in frequency, then this may destroy the coupling effect, if it is too small. You get it with piano strings too. Where two or more are tuned to the same note. The delta in tuning has an important on the sustain-decay profile of the notes. Arguing that entrainment must exist to some degree between two clocks is easy. Showing exactly what causes it is a lot harder. That is what the recent paper was about.

    • norbert wiener once proposed a birth control system consisting of transmitters with a 28-day cycle so all the women's fertile moments would be precisely predictable, based on the same principle

    • Re:Massive Huygens entrainment. (Score:5, Informative)

      by gwernol ( 167574 ) on Thursday February 21, 2002 @12:32PM (#3045074)

      I one had a posting from an old steam train worker on Africa somwhere. They used to have pairs of back-to-back steam engines for pulling heavy trains. The drive wheels used to have a random scatter in the diameter, and people in the engine shed used to try and match up sets of driving wheels with the same diameter, because that made the enginges 'run more smoothly'. From his account, it seems that on long, straight sections of track, the two engines would lock into step, but only if the wheels were a near match on both engines.

      This is a relatively well-known phenomenon on steam railways. A good example if the Ffestiniog Railway [festrail.co.uk] in Wales which runs the (now) unique Fairlie double engines [festrail.co.uk]. These locomotives have two boilers and two mechanically separate engine units that swively independently on pivots under the main frames. You can see this on the photograph here [festrail.co.uk]. Effectively these are two back-to-back locomotives joined together.

      The two engine units will synchronize when the locomotives run on relatively straight sections of track. Again the prevailing theory is that the synchronization occurs because of vibrations transmitted through the main frame.

      The Ffestiniog also has a pair [festrail.co.uk] of near-identical Hunslet [festrail.co.uk] locomotives that are sometimes run double-headed. These will also synchronize to each other, again presumably synching through the vibrations transmitted between them. Its interesting that the locos have to be of similar types for the synchronization to occur: it doesn't happen when dissimilar locos double-head. Going back to clocks, I would guess that the phenomenon does not happen when the pendulum lengths or other characteristics of the clocks are different.

  • Magnetic? (Score:2, Interesting)

    by vrmlknight ( 309019 )
    Could the pendulums be iron ferrite or have trace elements of magnetic metals?
  • Obviously the government put spyware in the clocks to make them synchronize and thereby suppress individual freedom, not to mention lack of support for .NET.

  • Unreasonable analogy (Score:3, Funny)

    by srichman ( 231122 ) on Thursday February 21, 2002 @09:44AM (#3044097)
    Am I the only person who was instantly reminded of menstrual cycle synchronization [google.com]?


  • This phenomenon is known as rythym entrainment, and a few of us 'Old Ones' Grok it in fullness.

    "As Huygens surmised, the platform motion is the culprit: if we prevent the platform from moving, there is no synchronization at all."

    This statement is, of course, patently absurd. There simply does not appear to be any sync because of limited tools for observation. If one had patience one could wait for fullness and observe the effect.

    And as far as claiming that they stopped the platform from moving goes, did someone achieve the temperature my name describes and forget to tell me???

    Those who want a better understanding of this, and many other secrets of the universe may want to read ..... Stalking the Wild Pendulum [amazon.com]
    • And as far as claiming that they stopped the platform from moving goes, did someone achieve the temperature my name describes and forget to tell me???

      Presumably he meant periodic motion and not thermal energy within the platform itself.

      Those who want a better understanding of this, and many other secrets of the universe may want to read ..... Stalking the Wild Pendulum

      Or on the other hand, you may not. A quick look at the reviews and the sampler on Amazon showed me it's a crank's book. Read only if you want pseudoscience and sinister conspiracy theories.

      But then... I could be one of the Illuminati trying to DEFLECT YOU FROM THE TRUTH!!!!!!!!!!!!
      • "Or on the other hand, you may not. A quick look at the reviews and the sampler on Amazon showed me it's a crank's book. Read only if you want pseudoscience and sinister conspiracy theories."

        Of course, you should absolutely judge it with a quick look at reviews from people whose qualifications you know nothing of, rather than actually reading and judging it. Who was the crank again ???? And who was talking about thermal energy??? just because I mentioned absolute zero??? On second thought, don't read the book ... you'd never understand it anyway 8^}
  • "Huygens deduced that the crucial interaction for this effect came from ``imperceptible movements'' of the common frame supporting the two clocks."

    [snip]

    "As Huygens surmised, the platform motion is the culprit"

    Summary:
    Huygens, 1657: "I think the frame is wiggling."

    GATech, 1995: "Yes, the frame is wiggling."

    What an amazing scientific mystery that was...

    =)

  • I once had three strands of Christmas Tree lights, all the same brand, using the same neato-geewhize-ooo-aaa blinking controller. I set them to the same type of blinking, but they obviously started out of phase. The next morning they were all blinking exactly together, in phase, all three strands. And they stayed that way until I turned them off.

    I have tried to repeat this each Christmas since and have yet to see it again.

    Any explanations anyone?
  • From time to time,I hear stories of clocks stopping when their owners die. I consider a few of them reliable accounts. I wonder if these type of things are coincidential, or if there would be some sort of interaction going on here as well ?
    • From time to time,I hear stories of clocks stopping when their owners die. I consider a few of them reliable accounts. I wonder if these type of things are coincidential, or if there would be some sort of interaction going on here as well?

      An obvious interaction:

      The grandfater clock stops when grandfather dies because grandfather is the fellow who WOUND the darned thing.

      So it's not unreasonable for it to stop at roughly the time grandfather does. And if he's dying in the house with the clock, the family is likely to be around the bed when he goes or otherwise distracted.

      When they start paying attention to anything but granddad it's likely that they'll notice the stopped clock. They won't KNOW if it stopped EXACTLY when grandpa's heart did. But since it stopped roughly at that time, to the limits of their measurement (running when grandpa cried out, stopped next time we wanted to know the time), it's easy to believe it stopped right when grandpa did.
  • It's morphogenetic fields at work! How simple you are, to think it can be reduced to well-known actors of limited range.
  • Sounds to me like a vibrational mode of the water molecule: One big heavy oxygen atom with two hydrogen atoms as pendulums. They vibrate 180 degrees out of phase. It doesn't seem logical to me that they could oscillate in phase...

    moog
  • What's so difficult and puzzling about forced resonance?
  • Almost anything that oscillates and has some coupling between oscillators will lock up like this.

    I used to demonstrate this with a pair of 555 timer chips on a solderless breadboard. If set up to oscillate at the same frequency, they would phase-lock, because when the output transistor switched, it would cause a power dip. These things would lock up even at different frequencies; I was able to obtain locking at ratios like 6:7.

    This also occurs with periodic polling programs, like mailers. Programs that poll, then wait for a fixed time will, if polling the same server, lock into synchronization. Then they all poll at about the same time. This phenomenon was discovered in Sendmail in the early 1980s, by someone at Lawrence Livermore Labs.

  • In other news... (Score:4, Funny)

    by Nate Fox ( 1271 ) on Thursday February 21, 2002 @01:56PM (#3045820)
    the decades old question of why Guinness bubbles 'float' down the glass has been solved. Actually took some high end fluid modelling software to figure it out :)
    http://articles.thetechmag.com/articles/?0,0372,01 31010,00.html [thetechmag.com]
    Also a press release here: http://www.fluent.com/about/news/pr/pr5.htm [fluent.com]

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