The goal of this project is to demonstrate the relationship between atomic structure and mechanical stability. Three major crystal structures including face-centered cubic structure, body-centered cubic structure, and hexagonal closed-packed crystal structure were built with toothpick sticks and marshmallows by middle schoolers. The crystal structures were then connected into a bridge. To test the maximum load that the bridge can take, metallic washers were placed on the top of bridge.

The goal of this project is to show that mechanical failure depends on the size and curvature of preexisting crack. To motivate middles schoolers, an “perfect” (without crack) egg was squeezed uniformly by students. No mechanical failure occurred. Once a precrack is created, it is much easier to crack the egg. Following this demonstration, a few notches were cut with different lengths and curvatures on papers. One student sat in a roller chair, the other student pulled the paper. The paper may or may not fail depending on geometry of premade cracks.