Catenary

1. In mathematics, a catenary curve is the curve made by a chain suspended between two points, supporting a constant weight per length. It is the graph of:

y = cosh x

This is not the same as the curve made by a chain supporting a constant weight per horizontal length, as in a suspension bridge; that is a parabola.

2. A catenary structure consists of an overhead cable or cables used to deliver electricity to a railway locomotive, multiple unit, railcar, tram or trolleybus through a pantograph. An alternative system is a third rail.