The Rube Goldberg contraption I made is called a dog-feeding machine. The simple machines in my contraption are the screw, lever, spring, wheel and axle, and inclined plane. The science concepts used in my machine are gravity, push-pull, Newton’s law, and kinetic energy. In my Rube Goldberg machine the simple machine I used the most is the lever. There are 9 separate steps in my machine.