1. A dam which is constructed across a river to store water. it provides necessary potential energy to nozzles of a turbine it acts as water reservoir. It is constructed with masnary or R.C.C. Top surface of water in dam is called head race.

2.The pen stock is a large diameter pipe. It comes water under pressure from the water stored in a dam or reservoir to the turbines.The pen stock is usually made of reinforced concrete or steel.

1. A water turbine converts hydraulic energy in to mechanical energy.A water turbine can be set horizontal or vertical. The choice is governed by cost, type of turbine, building space and plant layout etc.

2. A tail race is a discharge canal into which water is discharged canal into which water is discharged from the turbine.

Difference of head race and tail race level is called gross head . Hg.

The head of water available of turbine inlet is called net head. H. It is the difference of gross head and the frictional head. Hit in pen stock i.e.,

Net head, H= Gross head, Hg=functional head,

Hf = frictional head from Darcy Weis back equation is given as;

Frictional head. Hf =$\frac{4f.l.v^{2}}{d2g}$

Where, f = friction factor

v = velocity of flow of water

L = Length of pipe.

d = Diameter of pipe.