Equal and OppositeTeach children about the principles of physics, particularly the wonders of momentum and energy, in a fun, hands-on way with the Newton's Cradle. Pull back the polished steel ball on one end and let it fall. When it hits, it transfers its energy to the ball at the far end of the line, setting it in motion. At a perfect hand held size, it fits on any desk or coffee table. 4 1/2" x 4 1/2" x 4". Recommended for ages 5 and up.