Impact-induced acceleration by obstacles

TL;DR

This paper investigates how obstacles can unexpectedly accelerate flexible objects during impact, confirming the phenomenon experimentally, analyzing its dependence on impact angle, and proposing a complex impact model.

Contribution

It provides the first quantitative analysis of obstacle-induced acceleration in flexible objects and introduces a delayed impact model accounting for angle dependence.

Findings

Obstacles can cause acceleration rather than deceleration of flexible objects.

The impact acceleration depends on the angle of incidence.

A characteristic delay length is essential for modeling the effect.

Abstract

We explore a surprising phenomenon in which an obstruction accelerates, rather than decelerates, a moving flexible object. It has been claimed that the right kind of discrete chain falling onto a table falls \emph{faster} than a free-falling body. We confirm and quantify this effect, reveal its complicated dependence on angle of incidence, and identify multiple operative mechanisms. Prior theories for direct impact onto flat surfaces, which involve a single constitutive parameter, match our data well if we account for a characteristic delay length that must impinge before the onset of excess acceleration. Our measurements provide a robust determination of this parameter. This supports the possibility of modeling such discrete structures as continuous bodies with a complicated constitutive law of impact that includes angle of incidence as an input.