Application of Bernoulli's theorem
(i) Lift of an aircraft wing
A section of an aircraft wing and the flow lines are shown in Fig. The orientation of the wing relative to the flow direction causes the flow lines to crowd together above the wing. This corresponds to increased velocity in this region and hence the pressure is reduced. But below the wing, the pressure is nearly equal to the atmospheric pressure. As a result of this, the upward force on the underside of the wing is greater than the downward force on the topside. Thus there is a net upward force or lift.
(ii) Blowing of roofs
During a storm, the roofs of huts or tinned roofs are blown off without any damage to other parts of the hut. The blowing wind creates a low pressure P1 on top of the roof. The pressure P2 under the roof is however greater than P1. Due to this pressure difference, the roof is lifted and blown off with the wind.
(iii) Bunsen burner
In a Bunsen burner, the gas comes out of the nozzle with high velocity. Due to this the pressure in the stem of the burner decreases. So, air from the atmosphere rushes into the burner.
(iv) Motion of two parallel boats
When two boats separated by a small distance row parallel to each other along the same direction, the velocity of water between the boats becomes very large compared to that on the outer sides. Because of this, the pressure in between the two boats gets reduced. The high pressure on the outer side pushes the boats inwards. As a result of this, the boats come closer and may even collide.
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