<meta charset="utf-8"><span data-mce-fragment="1">Experience gravity and use your imagination and engineering skills to build elaborate marble tracks for the Gravity Spheres. Gravitrax STEM track system is a fantastic early introduction to physics, teaching kids about gravity, magnetism, kinetic energy, and more! Use the blueprints included to get you started, then let your creativity soar! The Gravitrax track system can be expanded endlessly with extra track packs and add-ons. </span>