As we built this K’nex roller coaster we learned some surprising lessons. We discovered that gravity, mass, friction, and velocity all interact to make inanimate objects start and stop. We were tasked to work out  a desirable mass for our cars. This needed to be in a small range in order to make the car move under a specific amount of force. Without the required force it could not  have made it through the loop and all the way around the track. The car had to be moving with sufficient velocity creating  enough centripetal force to keep the car on the track at the top of the loop. In the end we had several failed attempts and had to make modifications to our designs. Resulting in a collaborative win!