ACCELERATION

Film Loop: Inertial Forces - Centripetal Acceleration

Length: 3:15 Min., Black and White, No Sound

This film loop was made at the Rotor Ride at Cedar Point, Sandusky, Ohio. The cylindrical rotating device has inside diameter 14 ft. and attains a maximum angular speed of 27 rev/min. From these data, the centripetal acceleration is 56 ft/sec squared, about 1.8 g. After full speed is reached, the floor drops down and the passengers remain affixed to the wall.

There are two equivalent ways of analyzing the situation. To an outside observer, the rotation is known to exist (relative to a inertial frame). The wall supplies an inward and upward force P; the resultant of this force and the weight mgis horizontal and is the centripetal force which causes the centripetal acceleration. The rider's outward force on the wall is the reaction to the force of the wall on the rider, and this force is not shown in the diagram because it acts on the wall, not the rider. An upward component of the force of the wall on the rider (friction) arises because of the normal component of the force between the rider and the wall.

From an insider's point of view, an outward inertial force has come into existence because of the acceleration of his frame of reference. This outward force can properly be called "centrifugal force" by an observer who is in the accelerated frame of reference. This force is identical in its effect to an outward gravitational force; it is "artificial gravity " of magnitude 1.8g. The rider considers himself to be in equilibrium under the action of three forces; P, mg, and the inertial force- ma. .

In the film, the camera views the action from both frames of reference. (The cameraman hand-holds the camera while enjoying the ride. No special support is used.) Viewed from inside the Rotor the resultant gravity is downward and outward, as shown by the beach ball which no longer hangs vertically.

The interior wall of the Rotor is of heavy padded fabric rough enough to supply the necessary friction. The coefficient of friction between this fabric and ordinary clothing is evidently somewhat greater than 0.55.