ABSTRACT
Acceleration certainly does not need to be constant, any function of speed versus time is possible, but assuming that acceleration will always be constant is both useful and reasonable. Useful because it keeps the mathematics of motion solely in the realm of algebra, rather than the more complex calculus. Reasonable because most moves on stage do occur with constant accelerations. Many theatre automation control systems generate a trapezoidal velocity motion profile for the scenery they move. Most motor drives, if not following the commands of an external control system, will themselves give a constant acceleration/deceleration motion to the motors they run. Even a flyman running a line-set by hand will provide a good approximation of such a move. The goal of any technique presented in an engineering book is to model the behavior of the real world as accurately as is needed for the situation being analyzed. For the movement of scenery on stage, there is no particular need for the mathematics to model a move to an accuracy beyond a tolerance of perhaps ±5%. If the calculated top speed of a wagon is 3 ft/sec, and the actual machine runs at 2.9 ft/sec, will anyone notice? Probably not. The balance between the accuracy of a mathematical model and its simplicity is always worth weighing. And so here, with constant acceleration, we have an acceptably accurate simple mathematical model of what happens in typical moves involving real scenery.
