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Ventury tube:
A ventury tube is used to measure the speed of flow of a fluid in a tube. It has a constriction in the tube. As the fluid passes through the constriction, its speed increases in accordance with the equation of continuity. The pressure thus decreases as required by the Bernoulli equation.
In the figure below, the fluid of density U flows through the Ventury tube. The area of cross section is A1 at wider part and A2 at the constriction. Let the speeds of the fluid at A1 and A2 be v1 and v2 , and the pressures, be p1 and p2 respectively. From Bernoulli’s equation,
Figure shows two vertical tubes connected to the Ventury tube at A1 and A2. If the difference in height of the liquid levels in the tubes is h, we have,
From the equation of continuity, A1 v1 = A2 v2 , substituting v1 in terms of v2 or vice versa in the equation above, the rate of flow of liquid passing through a cross section can be calculated by knowing the areas A1 and A2.
Lifting up of an aeroplane:
The shape of cross section of wings of an aeroplane is as shown in the figure above. When an aeroplane runs on a runway, due to aerodynamic shape of its wings, the streamlines of air are crowded above the wings compared to those below the wings. Thus, the air above the wings moves faster than that below the wings. According to the Bernoulli’s principle, the pressure above the wings decreases and that below the wings does not change. Due to this pressure difference, an upward force called the dynamic lift acts on the bottom of the wings of a plane. When this force becomes greater than the weight of aeroplane, the aeroplane takes off.
Working of an atomizer:
The action of the carburetor of an automobile engine, paint-gun, scent-spray or insect-sprayer is based on the Bernoulli’s principle. In all these, a tube T is dipped in a liquid as shown in the figure. Air is blown at high speed over the tip of this tube with the help of a piston P in the cylinder C. This high speed air creates low pressure over the tube, due to which the liquid rises in it and is then blown off in very small droplets with expelled air.
Blowing off of roofs by stormy wind:
When high speed, stormy wind blows over a roof top, it causes low pressure p above the roof in accordance with the Bernoulli’s principle. However, the air below the roof (i.e. inside the room) is still at the atmospheric pressure p0 . So, due to this difference in pressure, the roof is lifted up and is then blown off by the wind as shown
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