Principle of minimum sliding speed curve. There are two kinds of slideways, one is straight, the other is curved, and its sliding surface is wheel line. Assuming that the height of the two slides is the same, when two children with the same weight slide down from the top of the slide at the same time, the children who reach the ground first are not the children on the straight skateboard, but the children on the sliding surface of the roller line. Because children will slide down the slide because of gravity. When the slope of the skateboard surface is different, the gravity component in the sliding direction is also different. The greater the gravity component, the greater the acceleration and the faster the speed increases. Sliding down the straight slide, the acceleration of sliding is constant and the speed increases steadily. When the slide slides down along the rotation line, the slope of the first skateboard is very large, which makes the children who slide down get very high speed in a very short time. Although, in the second half of the decline, the slope gradually became smaller and the growth rate slowed down, but at this time the decline rate has become very large.

Therefore, in the whole sliding stage, the average speed of the slider sliding along the surface of the roller line is very high. Even if the length of slewing line skateboard is longer than that of straight skateboard, the sliding time of slewing line skateboard is shorter than that of straight skateboard. This has been proved in mathematics and physics. That is, under the same conditions at the same height, the time to slide down the wheel line is the shortest.