Gravitrax Starter Set. Experience the power of gravity with GraviTrax Starter Set! Use your imagination to build superb tracks and set the gravity spheres rolling. This STEM system is the ideal learning toy to teach kids about gravity, magnetism, and kinetic energy. With over 120 pieces and 18 different construction elements, the GraviTrax Starter Set offers everything you need to begin building your own action packed marble run. Discover how the laws of physics affect the journey your marble takes with curves, junctions, freefalls and even a cannon! Experiment using different heights and angles to control the speed of the marble to get it to the finish.