The upper array is raised 12 cm above the lower array and then rotated so that opposite magnetic poles align. As the upper array falls it picks up translational kinetic energy. Upon impacting the lower array, the collision is partially elastic, i.e., the upper array bounces off the lower array due to the repulsion of opposite magnetic poles. But the collision also induces both upper and lower arrays to rotate. Thus, some of the translational energy of the falling upper array transforms into rotational kinetic energy in a demonstration of the law of conservation of energy. Close analysis of the spinning arrays immediately after collision reveals that the pair of arrays rotate in opposite directions. For every action, there is an equal and opposite reaction in accordance with Newton's third law.