Place a ruler on the edge of a table, and throw a ball at its free end. The ruler will fall. However, if you cover a part of the ruler with a piece of paper and repeat the throw, then the ruler will remain on the table while the ball will bounce off it. Explain this phenomenon, and investigate the relevant parameters.
将一把尺子放在桌子边缘，然后将一个球投向尺子的自由端。尺子将会落下。然而，如果你用一张纸盖住尺子的一部分并重新投掷小球，那么尺子将保留在桌子上，而球会从尺子上弹开。解释这一现象，并研究相关参数。