SPRK STEM challenges are fun, interactive activities that challenge students to use creativity and team-work to move through simple steps of the design process in order to build Sphero-based creations. The Hydro-hypothesis challenge leverages Sphero's ability to swim to test whether or not students can build a contraption to transport a load (pennies) across a small body of water. This activity would provide an excellent opportunity to discuss the concepts of buoyancy, density, surface area, and what types of materials float in water.