Page:Model steam turbines; how to design and build them (IA modelsteamturbin00harrrich).pdf/15

Rh raised to a height h feet, the work done is evidently wh foot pounds, and this amount is called the potential or stored energy in the body, since it is evident that if the weight be let fall through the same height it will give out Wh foot pounds in doing so.

From equation (8) the heigh through which a body has fallen is given in terms of its velocity by

Rh

and since the energy given out in falling is Wh foot pounds,

Rh

The right-hand expression is known as the kinetic energy of the body or energy of motion, and will be found useful in calculating the pressure set up by a jet when impinging on the wheel vanes of a turbine.

Momentum, or quantity of motion, is given by the expression Mass × Velocity=$v²/2y$.

If a body travel along a plane surface without friction at a velocity v, and is suddenly struck so that its velocity is increased to v₂, the momentum is increased.


 * The initial momentum=$Wv²/2y$,


 * ,,   final         ,,        =$W×v/g$,