Some years ago i asked myself a question that I still can not answer. Here it is: 


A given tower consists of finite homogeneous cubic blocks staying one on another and equal to each other. What is the condition for stability of such tower?


First one can consider 2-dimensional analogue of this problem where 2-dimensional tower is staying on a real line. 



One problem about tower stability
**Stability** 


For all $k$ up to the total number of blocks $n$: the center of mass of the top $k$ blocks must lie above the surface of the $k+1$ block supporting them.


