The subject that I chose to investigate was energy and the forces and transfer of energy. The physical science teachers at my school end the year with an amusement park themed unit. The kids are always excited for this part of their instruction. An amusement park is something that most kids are familiar with and can relate the subject matter to it.
The webite: http://www.gamenet.com/game/Simulation-Games-Amuse-Park/ is where they can build their own amusement park. They can build rides and attract people to their park.
At an amusement park you can see all the forces of energy at work. I would also have them build rides to show off at our end of the year parent night. They would have to make them scale. This would pull in math standards to the unit