Understanding and enhancing the impact-induced tension of a falling chain

Abstract

When a falling chain strikes a surface, it can accelerate downwards faster than free-fall. This counterintuitive effect occurs when a tension is created in the chain above where it strikes the surface. The size of this tension, and how it is produced, depend on the type of chain used. For a chain made of rods that are slightly tilted from horizontal, the impact-induced tension is readily observable. Here are reported experimental observations on such a falling chain for two different situations: when the chain strikes an inclined surface, and when the chain's mass density decreases with height. It is found that both of these arrangements can increase the downward acceleration. To quantitatively describe these observations a theoretical model is developed. The model successfully predicts the chain's position and velocity, even when the top end approaches the surface, without any free parameters. The model also predicts that uniform rods are practically the best for producing large tensions.