Physics Playground is a game designed to teach the fundamentals of simple machines and basic physics concepts. We have found playing Physics Playground for as little as 3 hours can improve performance on a test assessing knowledge of simple machines.
Shute, V. J., Ventura, M., & Kim, Y. J. (2013). Assessment and learning of qualitative physics in Newton’s Playground. The Journal of Educational Research, 106, 423-430.
Shute, V. J. & Ventura, M. (2013). Measuring and supporting learning in games: Stealth assessment. Cambridge, MA: The MIT Press.