No, not Superman, but the Super Ball. Sold by the fantastically named Wham-O corporation (who also brought you Hula Hoops, Hacky Sacks, and Silly String), millions of the surprisingly springy spheres have thrilled countless children and adults with their high-flying antics.
But what on earth makes them so incredibly bouncy? Turns out the answer is all in the rubber.
The synthetic rubber, that is. Boasting the futuristic name "Zectron," it was patented in the 60s by a chemist named Norman Stingley, and its bizarre properties are the key to the Super Ball’s astonishing bounce.
And it really is astonishing. Try dropping one from about shoulder level, and watch how high it rebounds: if your ball is in good shape, it should be in the region of 90% of its original height. Compare that with other supposedly bouncy objects and you'll see it's indeed a class-leader.
Of course, the faster it’s going, the further it rebounds. An average adult can throw a Super Ball against the ground with sufficient force to make it bounce at least 30 feet in the air (and probably over the neighbor’s fence, never to be seen again). Wham-O even once made a Super Ball the size of a bowling ball and threw it off a hotel roof: it destroyed a car on its second bounce. Don’t try this at home.
Bounciness isn’t the only unusual physical property of Zectron. It also has a remarkably high amount of friction -- try to slide (not roll) a Super Ball over a smooth surface, and you'll see how much resistance it puts up. Try throwing one upwards and into a vertical wall, and you'll see the ball bounce multiple times back into the wall as it goes upwards. Physics is freaky stuff.
So what's in this Zectron stuff, anyhow? Here's the recipe. Take some polybutadiene (a commonplace synthetic rubber used to make everything from car tires to golf balls), and mix it in about a 100:1 ratio with sulphur. This process -- called “vulcanization” -- makes it more flexible and stable at higher temperatures. Then put it in a mold, sit about a fifty-thousand pound weight on top of it, and bake it in a 300-degree oven.
Easy, right? Not so much -- unless you have access to a moderately well-equipped laboratory, plenty of supplies, and more than a little know-how. Take it from us, it’s much easier to make like millions of other people and buy one from a vending machine for a quarter.
So that's what goes into one. But in order to understand what makes it so bouncy, you need to take a close look at exactly what’s going on when it hits the floor...and that’s going to mean some of that freaky physics we mentioned earlier.
As a Super Ball falls, it accelerates. When the ball hits the ground (or any other suitably solid object) it stops, momentarily storing the energy it gained during its fall by compressing itself, springlike, very slightly. Then an instant later it rebounds, turning that stored energy back into motion -- but this time in the opposite direction. Up it goes.
That applies to pretty much any bouncing object, of course. What makes the Super Ball different? Thermodynamics tells us that any time energy gets converted from one form into another, some gets lost -- usually as heat. Where the Super Ball excels is in how efficiently it can make that conversion: polybutadiene's molecular structure means only about 10% of the downward energy gets lost as the ball compresses, and that other 90% gets changed into upward motion as it rebounds.
Even the bounciest of lesser materials can’t match that. Tennis balls do well to recover 70% of their downward momentum after bouncing. Golf balls do better -- about 80% -- but aren’t anywhere near as much fun to play with. The basketball gets closest, but it’s still not on par with Zectron’s numbers.
So while the Super Ball may not quite be up there with the Man of Steel, it’s still the belle of the ball in the bounciness league. Is that enough to justify its “Super” moniker? Thanks to Zectron -- and more than a little help from some good old-fashioned physics -- we think so.