After our Life Science unit on Human Body, we've moved onto our Physical Science unit. I learned about the 6 simple machines: the screw, the lever, the pulley, the inclined plane, the wheel and axle, and the wedge. By combining these simple machines, you can make a compound machine, also called a Rube Goldberg machine!
Check out my "Cat-toy-pult":
"Give me a lever long enough and a fulcrum on which to place it, and I shall move the world." - Archimedes