Impulse machine, mostly this refers to Pelton wheel, here. However, in classical mechanics, an impulse is defined as the integral of a force with respect to time:

where

I is impulse (sometimes marked J),
F is the force, and
dt is an infinitesimal amount of time.

A simple derivation using Newton's second law yields:

In 1879, US developed a double bucket design, which exhausted the water to the side, eliminating some energy loss of the wheel which exhausted some water back against the center of the wheel.

In about 1895, some one improved on Pelton's half-cylindrical bucket form with an elliptical bucket that included a cut in it to allow the jet a cleaner bucket entry. This is the modern form of the Pelton turbine which today achieves up to 92% efficiency.

## Theory of operation

Flowing water is directed on to the blades of a turbine runner, creating a force on the blades. Since the runner is spinning, the force acts through a distance (force acting through a distance is the definition of work). In this way, energy is transferred from the water flow to the turbine.