There are two slides: one slide is diagonal; The other slide is an arc. If there are two children with the same weight, A and B, sliding down from the top O point of the slide at the same time, A slides down the diagonal slide and B slides down the arc slide, which child slides down to the bottom A point first? It is generally believed that the distance a glides is a straight line and the distance is the shortest, so a child arrives at point a first. This analysis is wrong. Because who can reach the bottom first is not only related to the length of the journey, but also related to the speed of sliding.

A glides along the diagonal OA, which is a uniform acceleration movement, and the speed starts from 0 and increases slowly and evenly; The downward speed of B along the arc also started from 0, but at first it was a steep slope, and the speed increased rapidly, which made B slide faster than A. Although it walked more than A, it was hard to say who reached the finish line first. After research, scientists found that as long as the arc chute is designed as a straight line, it can become the fastest chute.

The problem of finding the "steepest descent line" was first raised by Swiss mathematician John? Bernoulli proposed it. Later, with the efforts of Newton, Leibniz, Jacob, Bernoulli and others, it was found that the cycloidal arc in the horizontal direction descended faster than any curve. The solution of this problem laid the foundation for the later development of a very useful new branch of mathematics-variational method.