Playthings of Science

By Fred GuterlDec 1, 1996 6:00 AM


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The first time I saw the TwiddleFish, it was hanging forlornly from a thumbtack on my colleague’s corkboard. It didn’t look like much of a toy--a rubber shark about the size of a candy bar, mounted on a foot-and- half-long metal cable. I twiddled it--that is, I moved the cable back and forth between my thumb and forefinger--and it flopped like a sick shark. It needs water, said my colleague. Just like a fish. That’s the whole point.

Charles Pell, who invented the TwiddleFish, is in fact quite proud that his creation flops around like a dying fish out of water. To him, it’s a clue that he has hit on some basic mechanical truth about fish locomotion. Pell, the resident sculptor-artist-biologist at Duke University’s Bio-Design Studio, had been trying to learn how fish swim so well by building realistic models in the lab. For years he had been laboriously constructing finely detailed, anatomically accurate, hellishly complex models with wood and fiberglass for bones, rubber bands for tendons, and cable and string for ligaments, all held together with glue.

So when a colleague asked him to make a simple stationary model for an experiment on guppy mating habits, he understandably took the path of least resistance. He made a fish out of some rubber he had lying around and stuck a thin stick of bamboo into the back of its head. When he put the model guppy in a tank of water and turned it to face the real guppies-- accidentally twiddling the bamboo--he was shocked. The fish scooted forward with uncanny speed and force. I put it in the water, and sure enough, the stupid thing swam, he recalls. It was unsettling, eerie. You could see that it was swimming just like a real fish.

The research value of the soon-to-be-dubbed TwiddleFish was obvious from the start. There is some irreducible minimum required to get something moving through the water, and this fish is it, says Pell. There have been lots of explanations of how a fish manages to swim better than the laws of physics allow, but the TwiddleFish taught us that it doesn’t matter what kind of muscles the fish has, or what kind of scales. The only thing that matters is the stiffness of its body. Pell has made similar models of other fish, and they all swim like the real thing. When a fish swims forward, there’s a bending movement at the base of the head, and the wave travels down the fish’s body.

Many who have seen Pell’s fish think he is onto something. The U.S. Navy was so impressed that it is funding the development of some kind of TwiddleFish propulsion for boats. For Pell, however, the TwiddleFish raises other tough questions that have yet to be resolved. Chief among them: Will it make a good bathtub toy? Does it have the potential to be the next hula hoop or Rubik’s cube, or is it a toy only a nerd could love? The big toy makers are wary. One chain suggested enclosing the fish in a water- filled tank and using magnets to twiddle it from the outside, but Pell isn’t having it. I decided I wanted the fish to be in the hands of kids, he says, so they can really feel what’s going on. Pell has now perfected four different twiddlable fish--shark, clown fish, barracuda, and trout-- and a year ago he started his own company, TwidCo., to sell the toys. At last report, however, he hadn’t quit his day job.

Even if that big, mythical toy company were to promote the TwiddleFish in its purest incarnation, with a budget worthy of a moon shot, would this tell us anything about its true merit? Perhaps not. No scientist, let alone toy marketer, has ever been able to figure out exactly what makes a successful science toy. With this in mind, we at Discover did not think it wise to try to forecast the next fad. Nor did we seek to review purely educational toys, because, as Deborah Tassie of the Exploratorium in San Francisco put it, It helps take the guilt out of it when a toy is educational, but most people just want to be entertained. Instead we decided to shoot for the more modest goal of identifying a few toys that, like the TwiddleFish, are just plain cool. For a month, we submitted an arbitrarily collected group of science toys to an unscientific, thoroughly nonrigorous test: we left them out on a table for anybody who happened to wander by. What follows are the office favorites.

Knowing a cool toy when you see one is not always easy. Most toy inventors lack Charles Pell’s certitude. On a given day in 1987, for example, Joe Bendik didn’t realize that he was stepping on an emotional roller coaster when the word toy flashed through his consciousness. On that day, in his laboratory at a West Coast aerospace company, he happened to be playing around with some metal disks, twirling them on his desk at nonperpendicular angles, then watching them slowly spin and wobble to rest.

The motion of Bendik’s disks was no different from what millions of kids have already achieved with quarters and bottle caps, except Bendik’s disks were weighty, six inches or so in diameter and an inch or so thick; objects were attached to them so that they could be polished. The disks themselves had been machined until they gleamed. The smooth surfaces served to minimize energy loss due to vibrations at the point of contact between the disk’s edge and the surface of the desk. Once the disk was spun, it kept going for a long time--one minute, two minutes, five minutes- -all the while making a heck of an odd noise, a sort of ululating vibration (imagine a barbell weight rolling on the gym floor, or a crash cymbal that slips off its stand, or the steel rim of a truck wheel rolling onto blacktop). As the disk began to lose energy, its contact point, paradoxically, began to turn faster and faster, even though the disk actually rotated more slowly, while the ululating grew higher in pitch, until, the instant before it stopped altogether, it turned into an eerie whine that sounded like some alien weapon from Star Trek.

As Bendik played with the disk, he thought, Perhaps it would make a good toy. Should he patent it? Could you patent a metal disk? With an acute sense of urgency, he set out to optimize the effects, as he put it--to find the absolutely best size, shape, and material for his spinning disk toy. Even more immediate, however, was a problem of terminology. How to describe the motion of the disk? Although it certainly spun, it actually turned about its center slowly, if at all; and although in some fashion it could be said to roll, its edge always touched the desk at one point, so it actually stayed in one place the whole time. Bendik invented the verb to spoll.

In the next several years of evenings and weekends, Bendik grew fascinated with the physics of spolling disks. What keeps them spinning is angular momentum, a form of inertia. A disk would go on forever were it not for the vibration and friction between the disk’s edge and the surface on which it rests. As the disk turns, its edge traces a circle that is always smaller than its diameter, but as friction and vibration remove energy from the disk, its angle relative to the tabletop decreases and the circle traced by its edge grows wider. At the same time, as the disk revolves at a lower angle, the vertical distance that it needs to move to change the point of contact decreases, which means that this contact point moves around faster and faster, producing a higher and higher whine.

Even as Bendik’s own interest grew, the certainty that had gripped him at first turned to doubt. I thought, ‘Hey, I like it, but I’m a nerd.’ I started showing it to scientists, and they liked it, but I wasn’t sure if anybody else would. With great trepidation, he showed it to Louis Pearl, a friend of a friend who happened to own his own small toy business, Tangent Toy Company, in Sausalito, California. Louis loved it, says Bendik. He said, ‘Wow.’ That came as a great relief.

The result of Bendik’s work is Euler’s Disk (pronounced oiler, after the Swiss mathematician), a hockey-puck-size metal disk, covered with a colorful, confetti-like holographic pattern, that spolls on its own eight-inch-diameter shaving mirror.

When Euler’s Disk first arrived at Discover’s offices, I must confess I was not impressed. Later, as colleagues wandered in asking, What’s that?, as a steady march of the curious subjected me time and again to the disk’s whine, as one colleague in particular (we’ll call him Michael) actually absconded with the toy for days, gradually I began to think that perhaps Bendik, like Pell, was onto something primal, something fundamental to fun. My three-and-a-half-year-old daughter confirmed this impression on a visit to the office. She found the spolling fascinating, though she preferred to slam her hand on top of the disk before it had a chance to stop on its own.

Many of the toys that arrived at the office involved magnets: the chaotic pendulum, which jiggles erratically because it is repelled by a magnet in its base; the perpetual motion machine, which required not only a magnet but a 9-volt battery. But these were pale realizations of every magnetic toy maker’s true dream: the magnet that floats in midair.

It’s the kind of thing that seems possible, unless you know of a reason it’s not, says Bill Hones, a 48-year-old former commercial pilot. Nine years ago, Hones (aided and abetted by his father, Edward, a physicist at Los Alamos National Laboratory in New Mexico) got it into his head that he could arrange a bunch of permanent magnets so that their magnetic field lines converged on one spot directly over the base, and that in that one spot he could gently place a small magnet, which the field would stably support. But no matter what he did, he couldn’t achieve a magnetic field close enough to perfect--the magnet on top would always flip over, inverting its poles and falling onto the base. Only after six years of failure, when he was at the brink of despair, did he get the idea to try to levitate a magnetized spinning top. The gyroscopic force of a top, he realized, which keeps it pointing straight up and down, might just be enough to overcome the magnet’s tendency to flip over. Hones crafted a magnetized, thumb-size ceramic top, placed it on a plastic sheet over his magnetic base, set it spinning, lifted the plastic sheet slowly until the top settled onto its invisible aerial supports, and took the sheet away. Time and again, the top went flying off to the side.

Eventually he got the top to stay put in midair, but even the final product--the Levitron--is rather tetchy. I knew it’d be a fairly delicate balance, Hones says. It was very frustrating for a long time, as you know. Indeed, I know well. Because of its catalog description, which promised complete and total levitation, the Levitron created a buzz around the office. It came spilling out of the box: a small, heavy top, a heavy base (which contains nothing more than a square hunk of magnet; no need for all that fine-tuning after all), the piece of plastic, and what seemed like dozens of washers of varying sizes and weights. The instructions warned us that the slightest variation in temperature could affect the strength of the magnets and throw off the delicate balance between the weight of the top and the upward magnetic force. Too light, and the top careens off to the side; too heavy, and it does not levitate. Achieving proper balance by adding and subtracting washers, and mastering the technique of spinning the top without upsetting it are fine arts. It took Michael, whose enthusiasm for the Levitron was boundless, about two hours of practice before he could effortlessly get the top hovering. It took me three days. But once levitated and spinning serenely for long, long minutes on end, the little top was appropriately and honestly awesome in its elegance.

That which the levitron achieves so doggedly, the common soap bubble claims as its birthright. Bubbles are the ultimate in ephemera. Children invariably want to possess them, and invariably they cannot. They are quite good at destroying them, however, and this act brings its own secondary joy. But even the thrill of obliterating a delicate, gently drifting soap bubble is enhanced if the bubble is enormous, or if the bubble is indeed not one but two or three or more, all linked in a complex airy structure. The joy inherent in bubble complexity is the chief insight of Louis Pearl, who is not only the owner of Tangent Toy Company (and thus the marketer of Euler’s Disk) but also the self-proclaimed Bubble Man, aka the Pope of Soap. He has elevated bubble making to an art form.

Bubbles are so perfect, says Pearl. That’s what’s really so special about them. They form because soap molecules have a low tensile strength, which means soapy film can stretch without breaking, and once a film encloses a volume of air, it seeks to contract to its smallest area-- hence the spherical shape. Three equal-size bubbles will always attach to one another at 120-degree angles; four will meet at about 109 degrees.

The sine qua non of the Bubble Man’s art, and perhaps his greatest invention, is the bubble trumpet--a cone-shaped piece of plastic with a lip to keep the bubble solution (diluted dish detergent, plus some glycerin to make the bubbles last longer) from running off onto the floor. It holds enough soap to produce a very large bubble--two feet in diameter. In fact, two or more people, each with their own trumpet, can collaborate to produce a single gigantic bubble. Back in the early 1980s, when Pearl sold bubble trumpets on the streets of Berkeley, California, mammoth bubbles produced by teams of up to eight passersby regularly caused traffic jams on Telegraph Avenue, or so he claims. Now, however, it is the 1990s, and Pearl, who will soon turn 40, sells $1 million worth of bubble toys a year from his office in Sausalito. I want to be the Starbucks of bubbles, he says frankly.

In Pearl’s hands, the bubble trumpet does remarkable things. He has perfected the technique of manipulating bubbles in midair. He blows a medium-size bubble, detaches it from the bubble trumpet with a wave of his hand, and while it floats he blows another one and attaches the two. A cluster of six bubbles forms a small cube-shaped bubble in the center, which he further inflates with a straw (as long as the straw is dipped beforehand in soap, it won’t rupture the bubble’s surface). Twelve bubbles make a dodecahedron.

Pearl demonstrates these and other concoctions in an 18-minute video, which I watched with my daughter. As soon as it was over, we took our bubble trumpets straight to the basement. I made a two-bubble cluster with ease, and came close to making a spaceship bubble, but my centipede bubble was lame, and a cube-shaped bubble was out of the question, to her utter disappointment. Daddy, why can’t you do it? she asked. Because I haven’t had as much practice as the Bubble Man, I said. Daddy, she said, can we go upstairs and watch the bubble video again?

Video. Now there’s a science toy.

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