PHYSICS OF THE FAIR: MIDWAY RIDES DEPEND ON SCIENTIFIC APPROACH; CENTRIFUGAL FORCE FAIR'S ATTRACTION

Riders on the Gravitron stand against the inside wall of a rotating cylinder that gradually picks up speed until centrifugal force makes the ride's floor unnecessary.

Physics is hard at work at the SEMO District Fair.

In the Gravitron, centrifugal force is what the person going around in circles feels. Dr. Guilio Venezian, who teaches general physics and mechanics at Southeast Missouri State University, says the rider feels more and more centrifugal force as the machine speeds up, pushing the rider against the wall.

As the friction between the rider and the wall increases it becomes great enough to prevent the rider from falling.

After some quick calculations on a legal pad, Venezian estimates that the Gravitron has to make five revolutions per minute for the riders to achieve the sensation of standing in midair.

Another ride, Pharoah's Fury, is a gondola that slowly begins swinging from side to side, picking up on its own rhythm like a child on a swing set. Venezian calls these rhythms oscillations.

To make the gondola go higher, the machine that drives it has to oscillate at the same interval as the gondola would go naturally, he explains.

The payoff on Pharoah's Fury occurs at the moment the rider reaches the top of the arc. "The thrill is that you're almost weightless at the top," Venezian says.

That moment of near-weightlessness is achieved because the force of gravity and the centrifugal force operating in the opposite direction are in balance, the scientist says.

Traditional carnival attractions depend on the laws of physics, too. Bumper cars, for instance, operate in the same way trolleys do. The pole that sticks up from each car is a conduit for the current that passes between the metal ceiling and metal floor, powering the car's motor.

The Crystal Castle house of mirrors actually just plays tricks on your mind, Venezian says. The house is a maze of mirrors placed at right angles in addition to plain glass and open spaces, a combination intended to confuse.

"You don't know if you're looking at a single mirror or two and don't know which way to interpret them. It's playing with your brain," Venezian says.

The Tilt-A-Whirl and a number of other carnival rides operate on the principle that it's thrilling for our bodies to go in two different directions at once. "It's like going over a bump in the road," Venezian says. "Your organs are still trying to go straight."

The queasy feeling some carnival rides are able to generate -- carnies who operate such rides usually keep a bucket handy -- results from the rides' ability to disturb our sense of equilibrium, Venezian says.

This sense is maintained by the structures in the inner ear called the semicircular canal. When the brain processes the information that the down direction is tilted, some people get sick.

According to Venezian, nothing at the SEMO District Fair's carnival is technologically new. The Star Dancer, which boasts of its sophistication, is basically a merry-go-round, he says.

Not that the merry-go-round is exactly child's play. If someone riding on the merry-go-round wanted to toss an apple to someone else on the ride, the aim would have to compensate for the ride's rotation.

That's called the Coriolis Principle, named for the 18th century French scientist who discovered the phenomenon.

To aim long-range rockets at England during World War II, German scientists had to factor in the rotation of the Earth.

"A merry-go-round is like the Earth on a small scale," Venezian says.