I am trying to construct a Newton Scooter (one powered by Newton's Third Law) using a spring. Basically, I am supposed to make the scooter travel 1.5 meters. I've tried using a spring from a retractable pen, but the vehicle I constructed seems to be going nowhere. It seems as though too much of the spring's energy is being dissipated. I know that the force exerted by a spring depends on the Spring Constant (k) and the distance compressed (x). Thus, I just wanted to ask, should I get a stiffer string for my purpose or a easily compressible one? Do stiffer-springs have greater spring constant values? Is there a way I can efficiently transfer all of the Spring's potential energy into kinetic energy for the vehicle?