Schematic defining the tangential force.

Abstract

<p> is the component force perpendicular to the wall of the gate. is the component force parallel to the wall. The integral of over time t is the tangential momentum. here in the figure is the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115463#pone.0115463.e009" target="_blank">equation (1</a>).</p