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2
 v 
 g  h    g  h    v  2g (h  h 1 ) (7.16)
1
2
2
2
Thereby to measure the difference h  h we can define the
1
2
speed of fluid or gas and this method is used in pitot tube . The
pitot tube was invented by French engineer Henri Pitot in the early
18th century and was modified to its modern form in the mid-19th
century by French scientist Henry Darcy. It is widely used to

determine the airspeed .The basic pitot tube consists of a tube pointing
directly into the fluid flow(fig.7.6). As this tube contains fluid, a
pressure can be measured; the moving fluid is brought to rest

(stagnates) as there is no outlet to allow flow to continue. This
pressure is the stagnation pressure of the fluid, also known as the total
pressure or (particularly in aviation) the pitot pressure(stagnation

pressure = static pressure + dynamic pressure)
The modern digital pitot tube which measures the speed
of the wind is shown in fig.7.7

Figure 7.6
Figure 7.7

7.5 Viscosity

The phenomenon internal friction or viscosity of a liquid
exhibits when there is a relative shifting(displacement) of layers of fluid

with respect to other layers. Generally speaking this phenomenon is
related to the transport (transfer) of the momentum of fluid particles

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