When making a Rube-Goldberg machine, it is important to remember to think about where the energy to keep your machine going will come from.
Learn about potential and kinetic energy:
Potential and Kinetic energy videoHere’s a explanation of elastic potential energy:
Elastic Potential Energy from Flipping Physics (first 4 minutes are best)The force of friction will also be important to consider:
What is Friction?
Source:: Mme Sarah’s Blog