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Science

Stone Skipping the Scientific Way 209

Posted by michael from the hop-skip-and-jump dept.
Quirk writes "National Geographic has a bit on the scientific analysis of stone skipping. Using a machine launching aluminum disks Lyderic Bocquet, a physics professor at the University of Lyon, and his colleagues discovered the 'magic angle' of 20 degrees as that required to maximize skipping. 'Jerdone Coleman McGhee of Wimberley, Texas, holds the current Guinness Book of World Records title for a 1992 toss that yielded an impressive 38 bounces across the Blanco River in central Texas'"
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Stone Skipping the Scientific Way More

Stone Skipping the Scientific Way

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  • Just wondering . . . (Score:5, Interesting)

    by millisa ( 151093 ) on Saturday January 10, 2004 @01:00AM (#7935858)
    I am horrible at skipping stones, but the best I ever got was on lake oneida up in NY right before it froze over (I think it was like 10 skips; yeah, I suck). I wonder how much the other type of degrees (temperature) effects things . . . physics/chem geek want to wax eloquent?

  • mass versus skip number (Score:5, Funny)

    by potpie ( 706881 ) on Saturday January 10, 2004 @01:00AM (#7935860) Journal
    What we should REALLY be trying to figure out is how to skip more massive stones. That's the next step.

    This one time, me and some people were skipping stones *hardcore* style. We got the biggest flat rocks we could lift and tried to spin them. Usually they just glided, but sometimes they would skip fairly high.

    Of course, once the government got hold of this technology, they would put it to use bombing Iraq.

    • Re:mass versus skip number (Score:5, Funny)

      by Tyler Eaves ( 344284 ) on Saturday January 10, 2004 @01:05AM (#7935890)
      Or use it to take out a dam or something...
      • Who knows, they might even use it to land a rover on mars.

      • Re:mass versus skip number (Score:5, Interesting)

        by Dylan2000 ( 592069 ) on Saturday January 10, 2004 @09:49AM (#7937171) Homepage
        Wish I had Mod points, cause that was funny. For all mods who didn't understand or who are reading at +2 please click [imdb.com] and read about the British scientist who created a bomb which skiped along the water surface, impacted the wall of a dam, rolled down to the wall's base and then exploded, destroying an important German manufacturing area in WWII.

        Great film, but also some awesome science.
        • Great film, but also some awesome science.

          And a film you don't often see on the tube without some editing. A frequently-appearing character in it is the squadron commander's black Labrador, whose name didn't cause any problem in a wartime British film but would not go over well on USAn TV today..

          rj

    • Actually, I *have* skipped bricks on the Niagara river (living a few minutes from the Falls). To answer the previous poster about what the variables might be, just IMHO:

      1. Angle of attack
      2. area of rock surface
      3. rate of spin
      4. velocity
      5. flatness of surface

      Somehow these all interract; for example, its difficult for me to skip a stone below a certain weight/area.

    • Some serious skipping was done during World War II. From http://www.kensmen.com/combatlessons4.html ".... In dropping bombs, the bombardier should allow for at least a 60 ft.. bounce and skip ..."

    • You mean like dambusters? (Score:5, Interesting)

      by adept256 ( 732470 ) on Saturday January 10, 2004 @01:35AM (#7936034)
      The massive spinning bombs that were designed to bounce along the water before sinking and exploding in front of a dam? That technology was developed and used successfully in world war II by the english.

    • Re:mass versus skip number (Score:4, Insightful)

      by Bob Cat - NYMPHS ( 313647 ) on Saturday January 10, 2004 @04:55AM (#7936605) Homepage
      There is a lot of military research on skipping bombs, see PBS [pbs.org]
    • Of course, once the government got hold of this technology, they would put it to use bombing Iraq.

      Actually, that's been already done. Not in this war, and surprisingly, it did not involve Iraq (though bonus points will be awarded for proving there is a link after all).

      The bombing method the Dambusters [dambusters.org.uk] used during WW2 employed a similar principle of skipping stones.

  • Personally (Score:2, Funny)

    by maelstrom ( 638 ) *
    I think this [www.cbc.ca] is much more about bored scientists.

  • Umm why? (Score:4, Insightful)

    by Anonymous Coward on Saturday January 10, 2004 @01:01AM (#7935863)
    Why do a scientific analysis of something when you ignore the #1 variable: The Stone.

    • Re:Umm why? (Score:4, Informative)

      by momerath2003 ( 606823 ) * on Saturday January 10, 2004 @02:12AM (#7936149) Journal
      Pay attention, and RTFA:

      Using the machine, which launches aluminum discs across a pool of water, the researchers arrived at the "magic angle" of 20 degrees.
      • From my experience, you would want things that are denser than aluminum to be used to skip stones-- they retain more energy as they skip through the water.

        • Re:Umm why? (Score:2, Funny)

          by IM6100 ( 692796 )
          Apparently it was a low budget operation. To do it right, they should have been shaped marble stones. Precision machined, anb with flatness measured on a granite surface plate, of course, to keep the people obsessed with making measurements happy.
      • It seems rather obvious that the AC did RTFA. As you even pointed out, they used aluminum discs, not stones. There's no mention of how well their discs approximate a stone in weight/shape etc.

    • Re:Umm why? (Score:2, Funny)

      by Anonymous Coward
      ...consider a spherical cow...
  • I suppose this kind of research fall under 'basic science'?

  • once again (Score:5, Funny)

    by the-build-chicken ( 644253 ) on Saturday January 10, 2004 @01:04AM (#7935886)
    ...good to see tax payer/student dollars at work
    • Or as they say on fark [fark.com], ``still no cure for cancer.''

    • Re:once again (Score:2, Insightful)

      by perplexo ( 717840 )
      Yeah, I agree to a certain extent... But isn't it the goal of science to learn more about the laws that govern the environment/world/planet/universe/what-have-you that surrounds us?

      Yes, it's kind of trivial. But there's some value in every bit of knowledge humans gain, no matter how small.
    • How do you suppose NASA ever decided on the correct reentry angle for spacecraft? That's right...

      • And to further elaborate on this, a space-plane based on this technique was in the early planning stages in the 60s. Based on what they learned from the X-15 and other projects, it was designed to achieve suborbital flight by skipping off the atmosphere. Google for the unfortunately named "dynasoar" and/or "dynamic soaring". AFAIK, the only relic that survives is a small model in the Smithsonian Air and Space museum in downtown DC. The Dynasoar program was canceled because expendable boosters were the b

    • ...good to see tax payer/student dollars at work

      This is *exactly* the kind of science that your tax dollars are best spent on. Many if not most major discoveries arise out of scientific playfulness, and are not as often accompanied by a cry of "Eureka!" as "this is funny..."

      Studies like "higher crop yields through controlling water salinity" might give a few people some more dollars, but is highly unlikely to lead to any major scientific discovery. I'd rather see playful experiments like this and the

  • To all the Minnesota geeks (Score:5, Informative)

    by teamhasnoi ( 554944 ) <teamhasnoi AT yahoo DOT com> on Saturday January 10, 2004 @01:04AM (#7935887) Journal
    and others who visit, if you are into stone skipping, Lake Superior is the place to go.

    Zillions of years of waves busting up the tough rocks has polished them all smooth and flat. This makes for some of the best skipping stones ever. We're talking about an endless supply here.

    Some of the piles I've seen reach 3 to 4 feet in height and run for hundreds of yards down the beach; all made up of beautiful rocks. If you're lucky you can find some other nifty stuff like beach glass or driftwood. And not so nifty stuff, like dead fish and RIAA jackets.

    • Sell em on Ebay

    • Lake Superior slashdotted (Score:5, Funny)

      by InfiniteWisdom ( 530090 ) on Saturday January 10, 2004 @02:32AM (#7936221) Homepage

      Mysterious Rock Movements
      January 12, 2003
      Lake Superior, Minnesota

      Scientists and local authorities are struggling to explain the sudden rise in the level of lake Superior. After long investigation the rise was attributed to a big pile of mostly flat rocks that somehow made their way into a pile a few meters from the shore. There was also a smaller pile of not-so-flat rocks much closer to the shore.

      Invstigators attempting to trace the people behind this strange event have only a few puzzling clues to guide them. The whole beach appears to bave been trampled by hundreds of thousands of people. The only clues to their presence is all those strange conical pieces of tin-foil with the base roughly the size of a human head. There were also a number of RIAA jackets nailed to tree stumps and impaled with darts.

      Darl McBride, strangely showed up and shoved the following quote down our throats: "I'm not sure who is behind this, but I'm certain we own the intellectual property. We can't tell you quite what the property is or how it was violated, but please send us $699"
    • Look like that lake of yours is gonna feel the Slashdot effect.

      Of course, it's a big enough server (surfer?) so it should be able to handle it.
    • Heard about a sucker bet one pro golfer used to make - that he could drive a ball for a mile or more, provided he could choose the course, time, and season for the shot.

      The course he selected was in or near Chicago, having a tee on a cliff overlooking Lake Michigan. The season chosen was mid winter - on a day and time when the ice would be solid but still flat and the wind strong and from the west. (It's not called "The Windy City" for nothing.)

      He'd tee off backward, shooting the ball out onto the lake

  • Well that's all fine and dandy... (Score:5, Interesting)

    by PoitNarf ( 160194 ) on Saturday January 10, 2004 @01:06AM (#7935898)
    that a human can skip one 38 times, but there is no mention on how many times the machine they built was able to do it. Just watch, this is gonna lead to some wacky robotics competition where teams try to construct different robotic launchers to see which can skip more times or longer distance.
    • I was feeling jipped at the end of the article too.

      In the near future, Bocquet said he and his colleagues hope to attempt the world record with their machine, testing the equations and theory of what's required to achieve the maximum number of bounces.

      Come on! In the near future?!? How many damn skips did the freakin' robot get? They mention the record twice in the article. The least they coudl have done is said 'the robot is getting 18-20 Skips right now, but once we tune it up we hope to have s shot

    • Re:Well that's all fine and dandy... (Score:4, Interesting)

      by Cat_Byte ( 621676 ) on Saturday January 10, 2004 @01:47AM (#7936071) Journal
      I live near a river (100 yards away) and grew up here. Personally the 38 skip record sounds weird to me since you can skip a small one many more times than that with the near flat angle of entry & make the skips about 1" apart. I've never counted but I would estimate over 50 from the continuous stream of splashes as it skims the water.

      Now here is the kicker. If it's on a river the water isn't perfectly flat. I wonder if their "magic angle" took wave size into account? You really have to get a higher angle to keep it from diving into waves if necessary. No I didn't RTFA. It was /.ed.

      • Re:Well that's all fine and dandy... (Score:4, Interesting)

        by XNormal ( 8617 ) on Saturday January 10, 2004 @09:22AM (#7937097) Homepage
        Now here is the kicker. If it's on a river the water isn't perfectly flat.

        It depends on the amplitude of the waves. On each skip a random angle added or subtracted from the ideal 20 degrees. If this minimum of energy loss per skip around 20 degrees is relatively symmetrical you should still get the optimum at 20 degrees. For really high wave amplitudes you might hit the water at an angle that is too sharp and not skip at all so in those cases a shallower angle may be preferred.

        Personally the 38 skip record sounds weird to me... ... I've never counted...

        Consider the possibilty that your estimate is incorrect. Even 25 skips looks like "a lot".
    • Launchers? No no no... we'll be skipping the robots next. Perhaps we can develop self-powered skipping robots that, once initially thrown, will continue indefinitely. They may even be steerable. How that's for a competition?

  • Just what I expected... (Score:5, Funny)

    by Code-Ex ( 655722 ) on Saturday January 10, 2004 @01:07AM (#7935903)
    ...geeks bringing a stone skipping machine to tweak and experiment with while they go camping with their Wi-Fi gear. Can't we have a normal camping trip? =)

  • Awwww (Score:3, Funny)

    by NiTr|c ( 130325 ) <hackop.inumbrate@net> on Saturday January 10, 2004 @01:07AM (#7935905) Homepage
    My innocent childhood hobby has been ruined with the introduction of science and actual calculations! Not to mention that I've only ever been able to get like five skips. *runs to hide*

  • All about salt water (Score:4, Interesting)

    by Anonymous Coward on Saturday January 10, 2004 @01:08AM (#7935907)
    You centrally located people haven't experienced stone skipping until you have been to the ocean. Easy to get 15-20 skips in a calm inlet. Dense salt water makes it that much easier.

    I'm sure at the dead sea you could really make 'em go.
    • I tried it, but I was only able to get 3 or 4 skips (although the fact that it was 115 degrees out and I was suffering from heatstroke might've had something to do with it).
  • I have witnessed a guy in MINNEHAHA SPRINGS [wvculture.org], WVA skip a stone over fifty times. It was on a man made lake with a bank that contained many large peices of slate which were ideal for skipping. When watching him skiped, I noticed that he threw the stones with a slight curve.

    • I have witnessed a guy in MINNEHAHA SPRINGS, WVA skip a stone over fifty times. It was on a man made lake with a bank that contained many large peices of slate which were ideal for skipping. When watching him skiped, I noticed that he threw the stones with a slight curve.

      Hmmm, just out of curiosity how do you know 'over fifty time'? I mean, thinking about it, given a 'skip time' of, say, 3 seconds that a bounce every 0.06 seconds. Even a rather optomistic 15 seconds gives a skip every 3 tenths. How o

      • We had seen one of his videotapes and could reasonably guess that it the stone skipped over fifty times. In these kind of skips, the stone will skip something like 12 times in what looks kind of like a skid, after each skid, the stone files up again and repeats the skidding process. This happened five times to the stone, with each skid shorter than the last. In other words, all of the skips do not take nearly the same amount of time, some are extremely short and fast while other are more familiar, longe

  • Proving yet again.... (Score:3, Insightful)

    by mark-t ( 151149 ) <markt AT nerdflat DOT com> on Saturday January 10, 2004 @01:15AM (#7935938) Journal
    ... that some people have entirely too much time on their hands. :)

    • Re:Proving yet again.... (Score:4, Insightful)

      by CodeMunch ( 95290 ) on Saturday January 10, 2004 @01:53AM (#7936093) Homepage
      It isn't entirely uselsss. "skipping stones" was the tech behind the bouncing bombs [google.ca] in WWII that the Allies used to destroy German dams to deprive their industry of water. A couple weeks ago there was a great documentary about it on t.v. but i can't find a link - wuz on discovery or history channel i think - might have been one of those "dangerous jobs" shows. The bombs would bounce across the water & timed so that they would sink when they got up close to the dam and then detonate deep under water against the structure. Unfortunately, my words do not do the program justice.

  • A well researched problem already? (Score:5, Interesting)

    by wrmrxxx ( 696969 ) on Saturday January 10, 2004 @01:18AM (#7935951)
    The article suggests that this is the first time this type of problem has been scientifically studied. As far as I know this kind of problem has been very thoroughly studied for aerospace purposes: a planet's atmosphere is the pond, and a spacecraft is the stone. A google search for 'skip trajectory' shows up lots of serious research.

  • Original Paper (Score:5, Informative)

    by otisaardvark ( 587437 ) on Saturday January 10, 2004 @01:19AM (#7935960)
    http://arxiv.org/pdf/physics/0210015 [arxiv.org]

    Warning: not for the faint-hearted!

  • Stone initial conditions? (Score:4, Insightful)

    by mod_parent_down ( 692943 ) on Saturday January 10, 2004 @01:23AM (#7935980)
    The article mentions varying the initial conditions of release angle, velocity, angular velocity, but never talks about using different shapes of stones (discs).

    Any disc golfer or ultimate frisbee player can tell you that changing the shape or weight of your disc can very significantly affect its dynamics. It could be that they've only found the ideal release conditions for the particular disc they were testing with.

  • Go to the source (Score:5, Informative)

    by A nonymous Coward ( 7548 ) * on Saturday January 10, 2004 @01:26AM (#7935992)
    Here [nature.com] is a news article in the science journal which has the original report.
    • I *knew* I"d seen that before. But it turns out there was another article before the one cited in this 2004 paper:



      Bocquet L. 2003. The physics of stone skipping. AMERICAN JOURNAL OF PHYSICS
      71,50-155.
      The motion of a stone skimming over a water surface is considered. A simplified description of the collisional process of the stone with water is proposed. The maximum number of bounces is estimated by considering both the slowing down of the stone and its angular stability. The conditions for a successful

  • I seem to remember a Scientific American article from years ago that determined, via slow-motion photography, that each time the stone hits, it flips over. Anyone else heard of this?

    Tim

    • Re:I could see it. . . (Score:4, Interesting)

      by Bastian ( 66383 ) on Saturday January 10, 2004 @01:50AM (#7936079)
      I mean, the trailing edge is the edge that will hit the water first if you're talking a 20 degree angle, and if the stone skipped, the center of force would have to be behind the stone's center of gravity (otherwise it would sink).

      If it skips soon enough, it could be far enough behind the center of gravity to cause the stone to flip. But I doubt it happens all the time, because I can't see getting it to flip the same speed every time. If it doesn't flip by about 180%, the stone would soon hit at a bad angle and sink. The chances of even getting three or four skips in a row would probably be ridiculously small, but I can get at least that many skips fairly consistently.

    • Re:Don't the stones flip? (Score:4, Interesting)

      by dlakelan ( 43245 ) <dlakelan&street-artists,org> on Saturday January 10, 2004 @03:37AM (#7936379) Homepage
      The stone is usually spinning around an axis that is more or less vertical. The angular momentum of the stone makes it much more difficult to flip over via forces exerted by the water interface. In order to have it flip over, the axis of the spin now has to become horizontal requiring a tremendous torque.

      A stone fired at a lake with no initial spin might easily tumble in the manner you're describing, but probably wouldn't skip nearly as well.

  • I was going to read the article... (Score:5, Funny)

    by Concerned Onlooker ( 473481 ) on Saturday January 10, 2004 @01:27AM (#7936001) Homepage Journal
    ...but I decided to skip it.

  • This is what science is all about! (Score:3, Funny)

    by Saeed al-Sahaf ( 665390 ) on Saturday January 10, 2004 @01:28AM (#7936007) Homepage
    This is what science is all about. Mars? Please. Nanotubes? Come on! Stealth? Get real. Now stone skipping, that's worth at least a Master's dissertation... This has the possibility to advance toy technology YEARS!
  • Only in GW Bush's homestate would National Geographic stoop this low. Next they'll be flinging cow pies.

  • old news (Score:5, Informative)

    by alex_ant ( 535895 ) on Saturday January 10, 2004 @01:29AM (#7936009) Homepage Journal
    the allies figured this out in ww2. Nazi dam bombing [pbs.org]
  • How can this be applied to real-world applications? Are they going to redesign jet-skis with this information? Or surfboards or body-boards?

    Those are a few things this research could possibly apply to, can anyone give me examples of others?

  • Dam Busting Bombs (Score:5, Interesting)

    by _aa_ ( 63092 ) <j&uaau,ws> on Saturday January 10, 2004 @01:47AM (#7936068) Homepage Journal
    I recall watching a documentary about Barnes Wallis, a British scientist who during WWII invented and "perfected" a dam busting bomb. A rather large (multi ton) spinning cylinder full of explosives that would be dropped from a plane at remarkably low altitude over water directly at a dam at high speed, resulting in the bomb's skipping, like a stone, until it would collide with the dam. The bomb would then sink, but it's spinning motion would keep it tight to the dam until it exploded.

    Wallis' research involved countless stone skipping tests, that inevitably resulted in the discovery of the perfect angle.

    The bombs themselves enjoyed marginal success, succesfully destroying 1 of 3 objectives, if I'm not mistaken.

    http://simscience.org/cracks/dambusters.html [simscience.org] - Interesting videos and more information.

  • Skipping stones? That's easy... (Score:3, Funny)

    by stangbat ( 690193 ) on Saturday January 10, 2004 @02:01AM (#7936114)
    Getting a golf ball to skip...now that takes talent. Yeah, that's it. Talent...
    • Getting a golf ball to skip...now that takes talent. Yeah, that's it. Talent...
      There's a little 9-hole course near Boulder CO (Haystack Mtn Golf) with a lake on one fairway. Actually, the lake is the fairway. It's an easy 9-iron shot from teebox, over lake, onto green.
      Once, I topped the tee shot horribly, but imparted enough topspin that the ball skipped three times on the water and hopped out the other side
      ... where it promptly nailed the only tree in sight and bounced back into the middle of the la

  • skipping cannonballs (Score:4, Interesting)

    by tamarik ( 1163 ) on Saturday January 10, 2004 @02:26AM (#7936205) Homepage
    We recently sailed out to Ft Jefferson in the Dry Tortugas. We read where the soldiers would heat cannonballs to red hot and shoot them at enemy ships. They even made an oven with 4 magazines in it for the job. They used layers of wet and dry padding between the poweder and ball in the cannons. My pics don't say what size balls but they were one of 12, 18, or 32 lbs.

    These balls would skip along the saltwater and bury themselves in the ships at waterline level where the seamen couldn't get to them. The balls would then burn through the boats hull, hopefully starting a fire.

    See, there were even geeks back then with a lot of time and resources on their hands. This must have taken a lot of practice.

    Also visited Fort Pulaski outside of Savannah GA. These 2 forts were designed to be very similiar in so many aspects. But there is no mention here of this kind of ball skipping. Where Ft Jefferson is surrounded by water, though, Ft Pulaski only has it near in a 45degree arc, and that's more than a 1/4 mile away. The ships channel is out of cannonball range these days; maybe it wasn't back then.
  • Every year the folks who put out The Annals of Improbable Research [improb.com] , formerly The Journal of Irreproducible Results, formerly The Worm Runner's Digest hands out ten IgNobel Prizes [ignobel.org] for scientific achievements "which can not or should not be repeated". It's sort of a Feast of Misrule for science.

    If they can give an Ig for the first MRI images showing conclusively how men and women's bits fit together during coitus and a scientific study on the optimal way to dunk a biscuit in coffee, then by G-d this deserv

  • Aluminum disks? (Score:2, Insightful)

    by IM6100 ( 692796 )
    I'm sorry, but when I've skipped stones, half of the challange is finding the right flat stones. This whole experiment takes the fun out of it and turns it into a joyless exercise.

    I'd certainly hope this isn't going to lead to 'skipping stones' at the Olympics, or a standard skipping stone, produced by AMF and Wilson. Can't something just be fun without the jocks getting involved?

  • missing something (Score:3, Interesting)

    by CAIMLAS ( 41445 ) on Saturday January 10, 2004 @04:33AM (#7936546)
    It seems to me that they're missing several somethings that are fairly important (other than the physics of the stone): the velocity and spin of the stone (to say nothing of the water surface's dynamics).

    That said, my personal record was achieved when I was 12 at a cub/boy scount camp. It was in a little river/creek (maybe 10 feet across, no deeper than 1' in most parts, with lots of smallish smooth disc-shaped stones perfect for skipping). My group was out hiking, and we had a competition. Everyone else was picking more roughly-shaped stones off the shore, and not venturing into the water.

    Having grown up watching my uncles skip stones on their lake since I was very young, I probably knew a thing or two about stone skipping that the others didn't, simply by example. At any rate, I took a step or two out into the water, and grabbed the smoothest stone I could find.

    This was all after the scout master said the person with the most skips gets a candy bar. IIRC, I was the last to have my turn at winning the candy bar. Everyone started bitching about how I was cheating because I didn't take the rock from the shoreline. (bah!) I got into the water, and got as close as I could to the water, and threw the stone upstream like a frisby.

    The end result: 23 skips, at least half an hour of people trying to come close to half as many skips, and a candy bar for me back at camp. And a dozen pissed off cub scouts for 4 more days. :P

  • me too (Score:4, Funny)

    by prockcore ( 543967 ) on Saturday January 10, 2004 @07:19AM (#7936893)
    I skip the Stones whenever they're in town.

    I'm not paying $150 a ticket to see a zombie like Keith Richards.
  • I'll have to take one of those machines with me the next time I go camping by the lake - maybe I can link it to my WiFi enabled laptop and remotely skip stones from the comfort of my tent...

  • sad really (Score:2, Funny)

    by stewwy ( 687854 )
    and no one is going to believe it,(and I can't prove it) but I once managed 42 (answer to everything if you read douglas adams) on the River Mersey, mind you this was in the '70's and the river was more polluted then
  • the author was ridiculed on a french radio show by the name of "les grosses tetes". Since he was dealing with pros, he could not escape from the jokes ; a right-wing paper (Le Figaro) also nailed him for wasting taxpayers' money. Not many people realize that it's quite rare to find a scientist who actually publishes new research from time to time, and not standard crap ("we have worked on nanowhatever and not found anything worth mentioning but still publish it in order to get a pay rise")
    to increase his

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