What is a variable-speed, variable -power device?
A machine that must operate under conditions of speed and power that are not constant. An automobile, for instance, is a variable-speed, variable-power device because it should run smoothly and efficiently at any speed from one mile an hour to 60 miles per hour. And it requires variable power even without variable speed, because it needs more power on a grade, or for acceleration in traffic, than it does on a smooth, level road.
