Demonstrate Newton's first law of motion with this simple to use inertia demonstrator. This classic device demonstrates in simple terms that objects tend to "keep on doing what they're doing" unless acted upon by an unbalanced force. See product photo: When the metal post (spring) is pulled back and let go it strikes the plastic plate beneath the red ball and covering the blue receiver. Most students would be inclined to think the ball would be moved with the plastic plate, but in fact, it simply drops down into the blue receiver, demonstrating that an object will continue at rest unless acted upon by an external force.