he new Rollerball movie, directed by John "Predator" McTiernan from a screenplay by Larry "Alien 3" Ferguson and John "The Skulls" Pogue, is a semi-remake of the 1975 classic, written by William Harrison and directed by Norman Jewison (Jesus Christ Superstar). The original film—a telling social commentary on bloodlust and the rise of corporate power—was based on Harrison's Pulitzer-Prize-nominated 1974 short story "The Rollerball Murders," originally published in Esquire magazine. It has always been one of my favorite movies, and since I'm also an engineer and an avid player of indoor roller hockey, our humble editor has suggested I tell you all a thing or two about the physics of this brutal sport.
What is rollerball? The movies can explain that better than I can, but very briefly, it's a future spectacle which combines key elements of basketball, hockey, roller derby, motocross and kickboxing. Injuries are commonplace, and deaths are much less rare than in the sports of today.
In the Jewison film, players wear a traditional four-wheeled skate, with toe brakes which must be dragged along the playing surface in order to slow down or stop. Older readers will know exactly what I mean by this, and will realize that this arrangement makes it virtually impossible to brake while heading downhill (as opposed to today's heel brakes, which can't be applied while heading uphill). In the new McTiernan version, the players wear a high-performance in-line hockey skate which has no brakes at all. As with a pair of skis, steering and stopping are accomplished by turning the skates sharply against the direction of travel, with friction as the main limitation. Even with very sticky wheels, this makes for fast, dangerous action at high speed.
And high speed is the name of the game. The old track was a simple circle, an eighth of a mile in outer circumference, divided into six wedge-shaped sections identified with the letters A through F. The track consisted of an elevated ball gutter surrounding a ring-shaped playing surface inclined at 35 degrees, with a flat inner ring surrounding the two team dugouts and the referee's station. Thanks to gravity, a skater on the inclined portion of the track feels a lateral force pulling inward toward the center. When moving around the circle, he or she also feels a centrifugal force pulling outward—like the tug on your arm when you swing a bucket or a tennis racket. These two forces balance at V = (35m * 9.8m/s2 * tan(35))0.5 = 15.5 meters per second, or about 32 miles per hour. That is the most efficient speed for a rollerballer to travel—any faster and he will drift outward and upward, any slower and he will sink to the inner track.
Making sense of a
daring and deadly arena
These velocities are provided by specialized motorcycles—each 10-man team gets three of them, with handholds for easy towing and armored fronts for collision insurance. In fact, these cycles are capable of speeds in excess of 40 mph, although at higher speeds it would be very difficult to remain on the track without crashing into (or through) the outer barrier. The cycles and their drivers also present tempting targets for the opposing team, so a crack-the-whip maneuver can be used instead. This technique also exploits centrifugal force; when a line of skaters swing in an arc, they wind up accelerating the end member to very high velocity. If they let go at the right time, this skater is snapped down the track at full fighting speed.
The new track is more complicated—a figure-eight littered with the bumps and ramps and trick rails favored by 21st-century skaters—and the speeds are even higher, and the corners tighter. For brief intervals, the best skaters may even leave the track entirely, skating above the gutter on the vertical Plexiglas barrier which surrounds the track.
The game itself revolves around a steel ball approximately 14 centimeters in diameter, which would give it a weight of around 11 kilograms, or 20 pounds, if it were completely solid. The ball used in the movies appears to be somewhat lighter than this, so it's probably got a hollow center and a mass of around 5 kg. Impressively, this ball is fired from a cannon at 120 mph and is capable of circling the entire gutter before rolling down onto the skating surface.
This is critical to the game and very dangerous for the players, who skate counterclockwise around the track, while the ball is fired clockwise. This puts the net velocity between player and ball at 160 mph or more. Interestingly, the momentum of the ball (mV = 5 kg * 54 m/s = 270 kg-m/s) is about one-fifth as much as a skater (mV = 91 kg * 15 m/s = 1365), but its kinetic energy is more than two-thirds as much (0.5mV2 = 7290 joule vs. 10,237 joules). In other words, from a damage standpoint colliding with the ball is like hitting an anchored steel pillar at 20 miles an hour. So while the ball can't stop a skater in his tracks, it is more than capable of shattering an arm or leg.
Corporate evolution in action
Once the players manage to take control of the ball, it must be carried for one complete circuit around the track before it can be jammed or thrown into the funnel-shaped goal for a score. A dropped ball is out of play, but unlike in football, a dropped player can keep the ball alive simply by hanging onto it. Thus, the carrying team holds a definite advantage, but since either team can score with the ball, the opposing team has a strong motivation to take it away at any cost.
Make no mistake: rollerball is a full-contact affair, with all the hits and checks and tackles of any traditional sport and all the fiery crashes of traditional racing, plus such gladiatorial touches as razor-spiked gloves and the ball itself, which resembles nothing so much as a cannonball or the skull-smashing shotput invented by the classical Greeks. And since inflicting grievous injury results in only a three-minute penalty, and triggers the substitution of a weaker player or even leaves the enemy team a man short, there is little incentive to be friendly.
Jewison's answer was a mix of hockey and football armor—plastic pads over the shoulders, elbows and lower legs, with an open-faced helmet protected by nothing more than a chin bar. Aside from abrasion-resistant leather pants, no real concession was made to the awful physics of the track. The newer helmets—informed by the rise of inline hockey, extreme skating and goofy wrestling shows—include optional cage masks, plexiglass shields or goggles, side and throat covers and elaborate headdresses to wow the crowds and intimidate the opposition. But while these improved helmets can protect a skater's cranium in most falls and collisions, they provide no cervical support. The straight-on impact of a gutter ball or handlebar can easily snap a player's neck.
Other new equipment includes chin-to-toe leather cycling suits, optional spine and chest and abdomen protectors and razor-sharpened scoops for retrieving the ball. Any increased protection is easily offset by the greater hazards of the new game. All this points to one conclusion: rollerball makes for great spectacle and occasionally great sport, but its primary function is to endanger and wound and kill human beings, for the profit and amusement of a corporate culture gone badly awry. This was the whole point of "The Rollerball Murders," and it fits eerily well into the culture of the Twenty-Aughts. This, indeed, is one of the new movie's major charms: it is set, right here and now, in the grim and campy and hypocritical future Harrison predicted 30 years ago. And we do love the game, every bit as much as the MGM corporation wants us to.
Wil McCarthy is a rocket guidance engineer, robot designer, science fiction author and occasional aquanaut. He has contributed to three interplanetary spacecraft, five communication and weather satellites, a line of landmine-clearing robots, and some other "really cool stuff" he can't tell us about. His short fiction has graced the pages of Analog, Asimov's, Science Fiction Age and other major publications, and his novel-length works include Aggressor Six, the New York Times notable Bloom, and The Collapsium.
