This Newton's Second Law of Motion Apparatus is built from solid cast metal for years of reliable classroom use. The spring-driven mechanism is mounted on a substantial metal casting with all internal components visible, and the spring gun offers two tension settings. The base measures 10 inches by 2.5 inches, and the unit includes a 7.5-inch rod with a 0.5-inch diameter for mounting on a table clamp or support stand. Two steel balls are provided—one solid and one drilled—to demonstrate that both projectiles, when launched simultaneously, strike the ground at the same time regardless of horizontal velocity.