If you kick a ball down a sloping field, you can get to the goal much more quickly.
如果你在倾斜的场地上踢球,你可以更快地到达球门。
英语百科
Slope field
In mathematics, a slope field (or direction field) is a graphical representation of the solutions of a first-order differential equation. It is useful because it can be created without solving the differential equation analytically. The representation may be used to qualitatively visualize solutions, or to numerically approximate them.