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Science

The Physics of a Rolling Rubber Band 226

Posted by CmdrTaco
from the thank-god-that-is-solved dept.
sciencehabit writes "Modern physics can get complicated. Sure, researchers know exactly what forces act on a ball rolling down an incline — an experiment that helped Galileo develop universal laws for movement and acceleration. But what happens when a deformable shape like a rubber band rolls around? A new study reveals that the faster it goes, the more squashed it gets (video included)."
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The Physics of a Rolling Rubber Band

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  • Physics... (Score:3, Insightful)

    by Pojut (1027544) on Thursday July 29, 2010 @08:48AM (#33067626) Homepage

    ...is mind-boggingly awesome. I can't understand the math at all, but I understand the way things generally act. So cool (and so insanely complicated! Think about something like a key being inserted into a lock...and that's just simple, everyday stuff!)

    • Re:Physics... (Score:4, Interesting)

      by SpinningCone (1278698) on Thursday July 29, 2010 @09:01AM (#33067736)

      i agree. I always liked physics made the world look different (like "car breaks are kinetic to thermal energy converters"). never could really get into dynamics though. i remember my teacher describing the the problem of rotational inertia of a deformable object (like a jelly disk) faster you spin the more it changes shape which changes its inertia.

      props to the people out there with the knack and persistence to solve crap like that.

      • by Kupfernigk (1190345) on Thursday July 29, 2010 @09:11AM (#33067824)
        I'm sorry but this is such a common mis-spelling on Slashdot that it's getting to me. Cars have brakes. "Car breaks" means it stops working because of mechanical or electrical failure. Spellcheckers can't fix homophones.
        • by Anonymous Coward on Thursday July 29, 2010 @09:14AM (#33067860)

          Spellcheckers can't fix homophones.

          I can tell you have your spellchecker on, though I think you ment to write "homophobes".

          I too believe they should be fixed.

        • Cars have brakes. "Car breaks" means it stops working because of mechanical or electrical failure.

          I honestly thought he was talking about car crashes and even though that was a strange way of saying it, I convinced myselft that is was physically sound.

          • Re: (Score:3, Funny)

            by PiSkyHi (1049584)
            I think the key to this is that when a car brayx, it slows down and will eventually stop moving.
        • by ledow (319597)

          While we're at it, can someone please bring up the following:

          to/too/two
          there/they're/their
          your/you're
          whose/who's

          God, I know I'm pedantic but how hard is it to get *simple* things like this right? At least most of the time.
          It severely hinders my reading speed if some text has simple mistakes like that. My mind jars as it hits them and slows me down.

          • Re: (Score:2, Funny)

            by Anonymous Coward

            Tell that to two Slashdot users whose who's are wrong too. They're messing up their you'res while your there's are perfect.

          • by Guignol (159087)
            Thank's I would of right it so my self but you bit me to eat.
            I guess its fine I should of been more fasterer
          • How about "begs the question" used as "raises the question"? I know it's a lost cause but it still causes my eye to twitch.

            • by egomaniac (105476)

              I think you're on the wrong side of this one, obviously. Words and expressions change meaning over time, and at this point you might as well be upset over the fact that people use the word "computer" to mean "electronic calculating device" instead of its original meaning, "a person who performs tedious calculations by hand".

              It's time to give up and accept that you have lost the fight. "Begs the question" now means "raises the question".

          • by quadrox (1174915)

            Even worse, my mind has started to "crash" on rare occasions when people write "could have" instead of "could of" and similar stuff, simply because it is so rare to see it spelled right nowadays. That's really messed up.

          • by mhajicek (1582795)
            One of my pet peeves: "Less" vs. "Fewer". You can have "fewer people" under normal circumstances, but if you have "less people" it implies that they've been mashed up to the point you can't tell where one ends and the other begins, like oatmeal.
        • by Twinbee (767046)

          I was going to moan at you that it was obvious from the context that he meant 'brakes', but then someone goes and replies to you and thought he really did mean 'break'. Sigh... I was really going to enjoy the moan too ;)

        • by boxwood (1742976) on Thursday July 29, 2010 @11:58AM (#33070196)

          a bit of tape stuck over the bottom left corner can fix a homophone.

    • by Anonymusing (1450747) on Thursday July 29, 2010 @09:02AM (#33067742)

      Physics is pretty cool.

      I liked this quote from the article:

      As far as the potential applications, Clanet waxes futuristic. "I can imagine [designing] a car. The faster it goes, the more it deforms and the less friction it has with surrounding air, so it can go even faster. It would be a fantastic car."

      A car that changes its shape as it drives? Getting shorter, even? "Ouch, slow down, you hit my head!"

      Automobile safety experts would have a field day with that.

    • Re: (Score:2, Interesting)

      by Seismologist (617169)

      ...is mind-boggingly awesome.

      Actually you can often make a simple assumption and work off of F = m*a or some other well established theorem...

      As for the math, now that is some pretty mind boggling stuff. Some of the math that was used to pull string theory together is pretty bleeding edge on top of the physics part of it. PBS had a interesting show on string theory(you can watch in three installments on PBS [pbs.org]). What struck me the most was how splintered the physics community was as many researches were doing the math a certain way d

    • I didn't see this in TFA but I suspect they might find something a bit different about this behavior if they performed the rolling in a vacuum. I say this because some 15+ years ago I observed the deformation that they're talking about due to a magic trick I perform where I "shoot" a rubber band forward really fast and then it rolls back toward me like it was a boomerang, and it has little-to-nothing to do with aerodynamics; it has far more to do with the physical qualities of the "rubber" and the inertia o

  • by ZeroExistenZ (721849) on Thursday July 29, 2010 @08:51AM (#33067662)

    But what happens when a deformable shape like a rubber band rolls around?

    ... the article sounds like the things I used to wonder about and do during boring classes in highschool.

    • Re: (Score:3, Funny)

      by jamesh (87723)

      ... the article sounds like the things I used to wonder about and do during boring classes in highschool.

      Same here, except I was more like "I wonder if I can hit that kids sticking-out ears with a rubber band from here", without thinking through what would happen if i _did_ hit them (which should have been obvious in retrospect... it was for that reason I sat at the back).

      • ... the article sounds like the things I used to wonder about and do during boring classes in highschool.

        Same here, except I was more like "I wonder if I can hit that kids sticking-out ears with a rubber band from here", without thinking through what would happen if i _did_ hit them (which should have been obvious in retrospect... it was for that reason I sat at the back).

        ..guess it depends on how big the kid with the sticking-out ears was, eh?

      • by PitaBred (632671)

        If you want to make sure you do hit the ear, make one "side" of the rubber band tighter than the other when you shoot it. It makes it spin in flight and stabilizes it's trajectory. I can nail a fly from 10' with the right technique ;)

    • by Spad (470073) <slashdot@NOsPam.spad.co.uk> on Thursday July 29, 2010 @09:14AM (#33067856) Homepage

      I like to imagine that all scientists operate on this principle. They sit around doing boring paperwork until one of them says "I wonder what happens when a deformable shape like a rubber band rolls around?", to which one of the others replies "Quickly, to the lab!" and they all run off to investigate it.

      • I like to imagine that all scientists operate on this principle. They sit around doing boring paperwork until one of them says "I wonder what happens when a deformable shape like a rubber band rolls around?", to which one of the others replies "Quickly, to the lab!" and they all run off to investigate it.

        Actually, that's a pretty good description of lunch with physicists. Except, first we'd have to write down the physical constants of the rubber band, derive the dynamic equations of motion for the rubber ba

        • by gstoddart (321705)

          Actually, that's a pretty good description of lunch with physicists. Except, first we'd have to write down the physical constants of the rubber band, derive the dynamic equations of motion for the rubber band, find the expected behavior, and then run off to the lab to see if our results were correct with the last half of our lunchtime.

          So, what, physicists only do physics during lunch?

          The rest is all paperwork? How lame. :-P

          • So, what, physicists only do physics during lunch?

            No, first we each lunch. Then we get distracted. Everything else is paperwork. First you have the theoretical physics which is paperwork, then after you do the experiments and have to write down all your data and findings, then write up the paper, which is more paperwork.

    • by gl4ss (559668)
      if it's worth publishing, I'd have hoped for it to be worth to them to have an incline to roll it down on, instead of having it in a rolling drum. like, get out of the damn room if it's too small. now i'm just left wondering if it spun along with the drum and got squashed because of that.
      • if it's worth publishing, I'd have hoped for it to be worth to them to have an incline to roll it down on, instead of having it in a rolling drum. like, get out of the damn room if it's too small. now i'm just left wondering if it spun along with the drum and got squashed because of that.

        maybe they used a drum because setting-up a camera along a 50 foot ramp would've been cost-, space-, or effort-prohibitive?

        • by stomv (80392)

          but I'm surprised that they didn't get a bigger drum, in order to minimize the curvature of the surface with which the elastic was in contact. I have no idea if their model corrects for the fact that the elastic is not rolling down a 'flat' surface, but rather one with a curve. Bigger drum, smaller curve.

  • Wow, interesting! (Score:5, Interesting)

    by rotide (1015173) on Thursday July 29, 2010 @08:58AM (#33067722)

    If you would have asked me how it would react as it rolled faster and faster, I would have just assumed it would have gotten "rounder" and possibly larger (elastic) due to centrifugal force.

    Always amazes me how things don't always work as expected. Nature, physics, etc, are truly interesting... no, fascinating. Now if only I had a better grasp of higher level maths and wasn't a Network Engineer (data plumber).

    • by V!NCENT (1105021)

      "I would have just assumed it would have gotten "rounder" and possibly larger (elastic) due to centrifugal force"
      It does get round and evens out, but due to gravity the evened out band gets pulled down and the resistans on the 'outward ends' all result on a peanut form.

      Geez that was mind-bloooooowwwwwiiiiiing.......

      So how's the LHC doing?

    • by Spad (470073) <slashdot@NOsPam.spad.co.uk> on Thursday July 29, 2010 @09:16AM (#33067874) Homepage

      ...due to centrifugal force.

      My high school physics teacher used to electrocute (With a handheld generator made from a rotary pencil sharpener) people for saying that; also for misspelling accelerate or satellite.

      • by Yetihehe (971185)
        Obligatory xkcd link: http://www.xkcd.org/123/ [xkcd.org]
      • Re: (Score:2, Interesting)

        by silentcoder (1241496)

        >>...due to centrifugal force.

        >My high school physics teacher used to electrocute (With a handheld generator made from a rotary pencil sharpener) people for saying that; also for misspelling accelerate or satellite.

        Yes a common reaction of overzealous highschool teachers - and wrong. Do the math. Forces per se is an oversimplification as it is, useful to model certain aspects of physics, and not for others. Gravitons attract one another, thus is created what we PERCEIVE as the force of gravity if y

        • Also XKCD agrees with me which renders any arguments invalid.

        • by Guignol (159087)
          The overzalots teachers are right and misquoted.
          When they say 'there is no centrifugal force but instead a centripetal force' they don't say it our of nowhere at any time just to hurt your feelings
          Whenever a child get in school starting to learn basic physics, he almost always 'know' about the so called 'centrifugal force' meaning the force you experience when you are in a rotating wheel, orthe force that will prevent the water from falling in a fast rotating bucket attached to a rope (etc.)
          So the teache
          • You know we all also learned the right-hand law for electromagnetic inference and that ALSO disapears if the objects stop moving ... does that mean we can't model magnetic forces now ?

            • by Guignol (159087)
              Sorry I don't see your point (and I am not saying this in a way that would try to diminish it (really this is not an agressive answer in any way), I just don't see what you mean as far as my point is concerned)
              • You stated that we cannot model centrifugal force because it disappears if the component forces are removed (duh- remove either of them and there is no longer anything to add up to it).

                I pointed out how you can have forces created by other forces that aren't even directly part of them (you need a force to move a conductor through a magnetic field) and since we have no problem modeling those and predicting exactly what will happen if the motive force is removed - this has nothing to do with the usefulness of

                • by Guignol (159087)
                  Oh right, thanks for your answer
                  I didn't "state it" that's giving much more strenght thant what I meant as it was in fact not my point at all
                  but thanks for your answer, I see how you interpreted it.
                  My point was not on this part, that's a separate thing to debate on I don't completely agree with what I wrote per se, it was just part of the main point
                  To me the point was that I don't like physics teachers being 'ridiculed' (so to speak) around the centripetal/centrifugal force argument because
                  - I see i
                  • I have no problem with the point you make - my problem is with those teachers who when the smarter kids can USEFULLY model it as a force to solve problems quicker (fully understanding what's REALLY happening - that inertia is an effect of momentum is an effect of mass- maybe even know the Einsteinian addition that allows some things to have momentum WITHOUT having mass like photons) get punished for taking what to THEM is just a clever shortcut.

                    Clever shortcuts are a fundamental trick to being better things

      • ...due to centrifugal force.

        My high school physics teacher used to electrocute (With a handheld generator made from a rotary pencil sharpener) people for saying that; also for misspelling accelerate or satellite.

        ah yes... "centrifgual force" - that force applied by a centrifuge.

      • Re:Wow, interesting! (Score:5, Interesting)

        by ledow (319597) on Thursday July 29, 2010 @10:04AM (#33068478) Homepage

        Yes, but then people "weigh" themselves in kg's by standing on a scale that is affected by gravity.

        There are certain things that, although "visible" by ordinary people and named, don't actually exist or exist only because we *perceive* them to exist, like that optical illusion with the white triangle that isn't ACTUALLY there.

        Centrifugal force may be misnamed (i.e. not a force), it may be incorrect, but it's generally accepted that "a force" exists that has an effect on your when you're spun in a circle. Just because the direction / origin / name of that force is incorrect is no reason to tell people that they're stupid for having felt it and knowing what it is before you explain its origins.

        Back in the 60's there was an advertising campaign by scientists working on the behalf of government to target heat loss in elderly people's properties. It encouraged old people to "keep the heat in". It didn't go down well and it took them years to discover why. Eventually it was changed to "keep the cold out" and more elderly people understood that. "Cold" doesn't actually exist, it's just the absence of heat, but old people didn't think that way as easily (and who can blame them? "Shut the door, you're letting the cold in" is a common cry in my family - despite the fact that you're neither letting cold in nor arranging for some mystical "cold" entity to enter your property rather than, say, air with slightly less heat).

        There's 100% pedantic accuracy. There's complete bollocks. And somewhere in the middle is how *everybody* thinks, even if they know both extremes in detail.

        • by Twinbee (767046)

          Even on a pedantic level though, it's correct to say something's colder *relative* to something else, rather than as an absolute level of cold. Also bear in mind that they're talking about the sensation/feeling of cold rather than its physical makeup. On a certain level, red is best spoken about by its name rather than its wavelength. It's just a different kind of pedantic-ness, not necessarily less pedantic.

        • Re: (Score:3, Insightful)

          by Chris Burke (6130)

          Yeah, stupid meteorologists, talking about "cold fronts". No such thing! They should say "Fronts containing less heat." But then again all fronts contain heat, so what's a warm front? It's just warm compared to cold fronts.

          Maybe it's because of my electrical engineering schooling and years spent acting as if it was the positive charge carriers that were moving, but I don't see any problem with saying "let the cold in". Cold is a negative heat delta. Big whoop. When you open the door in the winter, co

    • Spinning faster = more velocity perpendicular to slope on the leading edge of the loop. It makes sense that it would flatten out.

      • Re: (Score:3, Interesting)

        "Spinning faster = more velocity perpendicular to slope on the leading edge of the loop. It makes sense that it would flatten out."

        Very good point. The back edge of the loop is being accelerated perpendicularly upward. IOW, the small length of rubber that's breaking contact with the table is yanked -- accelerated -- upward to a high vertical velocity. Therefore, it will rise higher that it does at a slower rolling speed. Like throwing a ball upward with a high velocity against gravity, it reaches a highe
    • by XSpud (801834)

      If you would have asked me how it would react as it rolled faster and faster, I would have just assumed it would have gotten "rounder" and possibly larger (elastic) due to centrifugal force.

      And I'd think for a suitably low coefficient of friction between the band and the ground you'd have been right.

  • However, if the rubber band is spinning really fast, aren't the centrifugal forces pushing the band outward, compensating the squashing?

    Disclaimer: I didn't RTFA.

    • Centrifugal force doesn’t exist. It is simply our perception of momentum in a spinning object.

      • Forces do not exist. They are simply our perception and our way of modeling certain aspects in nature. Centrifigal forces are simply a way of referring to the opposite of centripetal forces (in Newton's third law).

        But that was entirely not the point.

        • So what you are saying is, centrifugal force is the equal and opposite force to the force you must apply to move a rotating system’s centre of mass.

          No... that’s simply its momentum. Or its inertia, as they are the same thing.

    • by Culture20 (968837)

      However, if the rubber band is spinning really fast, aren't the centrifugal forces pushing the band outward, compensating the squashing?

      You also didn't read your physics book. There is no such thing as centrifugal force (outward from center).

  • by Anonymous Coward on Thursday July 29, 2010 @09:20AM (#33067914)

    For those of us where the player won't launch when you click "play video" in the article, here's a direct link to the flash video:

    http://sciencevideo.aaas.org/sciencenow/snow_ribbon_250.flv [aaas.org] (320x240, 17 seconds, 1.1MB)

  • by cangrande (199946) on Thursday July 29, 2010 @09:37AM (#33068140)

    All science videos are improved by Yakety Sax.

  • Miracle (Score:5, Funny)

    by JustOK (667959) on Thursday July 29, 2010 @09:40AM (#33068182) Journal

    Fucking rubber bands, how do they work?

    • "Fucking rubber bands, how do they work?

      Feynman to the rescue [youtube.com].

      The phenomena in TFA is just begging for a numerical simulation. I wonder if something like Blender or PhysX would predict this behaviour correctly?
      • by JustOK (667959)

        And I don't wanna talk to a scientist
        Y'all motherfuckers lying, and getting me pissed

  • It’s all about the deformability of the loop. In a perfectly circular loop, the intersection with the ground is tangential. If the loop deforms, it strikes the ground rather than intersecting tangentially, and the faster it spins, the harder it hits the ground. The harder it hits, the more it deforms.

    Alternately, as I see it, if it is accelerating due to its friction with the ground (i.e. if you spin it up first and then let it go) it should be able to temporarily keep itself supported under its own m

    • by pz (113803)

      It’s all about the deformability of the loop. In a perfectly circular loop, the intersection with the ground is tangential. If the loop deforms, it strikes the ground rather than intersecting tangentially, and the faster it spins, the harder it hits the ground. The harder it hits, the more it deforms.

      Alternately, as I see it, if it is accelerating due to its friction with the ground (i.e. if you spin it up first and then let it go) it should be able to temporarily keep itself supported under its own momentum, but as soon as that friction drops to zero it will begin to collapse due to its own weight and then the above will apply. As long as the frictional force vector is zero or points backward, the band should deform. Naturally I’ll be needing a few hundred thousand dollars to be testing my theory.

      Just watch a little top fuel drag racing to see tire (a/k/a elastic loop) deformation under load.

      • One could do that; however I do not think they are a very good subject to study this effect. They are moving too quickly to observe very well without high-speed camera equipment, heavily loaded (apart from their own weight), and designed to deform as little as possible under smooth conditions because tire deformation increases the drag on the vehicle (remember that over-inflating your tires will increase your gas mileage?).

    • It makes me wonder if this could all have been achieved by sitting down and working it all out from fundamental laws. It seems like it could have, although the experimental approach was probably faster!

  • Won't there be Centrifugal/Centripetal forces from the drive wheel it is running inside?

    Or do these forces not exist because the rubber band is essentially stable in it's position inside the wheel?

  • Ok so if I remember correctly, the center of a golf ball is made with a rubberband like substance, and then is covered with that nice hard plastic shell. But as a golf ball lands and rolls, wouldn't that spin cause the same reaction as what is in that video? Or could we assume that it is so tightly wound and then encased with little to no wiggle room that this alteration of shape would not take place? I'm thinking it's the latter.

    Next I'd love to see the same thing performed with the traditional egg drop

    • by teebob21 (947095)
      This.

      it is so tightly wound and then encased with little to no wiggle room that this alteration of shape would not take place.

  • by azmodean+1 (1328653) on Thursday July 29, 2010 @10:20AM (#33068670)

    I was amused by this aside:

    (The team couldn't study what happened when the two sides touched: The friction of the two sides moving in different directions sent the rubber bands flying out of the drum.)

    What? It seems pretty obvious that they could see exactly what happened when the two sides touched, "The friction of the two sides moving in different directions sent the rubber bands flying out of the drum".

  • Obvious (Score:4, Funny)

    by wcrowe (94389) on Thursday July 29, 2010 @05:44PM (#33076590)

    A new study reveals that the faster it goes, the more squashed it gets.

    Well duh. Of course it does. Anyone who has watched a Roadrunner cartoon knows that.

The bogosity meter just pegged.

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