14. Falling Tower

Identical discs are stacked one on top of another to form a freestanding tower. The bottom disc can be removed by applying a sudden horizontal force such that the rest of the tower will drop down onto the surface and the tower remains standing. Investigate the phenomenon and determine the conditions that allow the tower to remain standing.

1. disc是哪种的？和摩擦以及质量有关，网上或者店里买哪种的合适？
2. 怎么敲最下面一个（手敲？能不能有什么重复性的装置？）

http://stemfellowship.org/iypt-2020-references-2/iypt-2020-reference-problem-14-falling-tower/