Saurabh Koranglekar
(i)Attraction between two closely parallel moving boats (or buses):When two boats or buses move side by side in the same direction, the water (or air) in the region between them moves faster than that on the remote sides. Consequently in accordance with Bernoulli’s principle the pressure between them is reduced and hence due to pressure difference they are pulled towards each other creating the so called attraction. [Attraction between two closely parallel moving boats]
(ii)Working of an Aeroplane:This is also based on Bernoulli’s principle. The wings of the aeroplane are of the shape as shown in fig. Due to this specific shape of wings when the aeroplane runs, air passes at higher speed over it as compared to its lower surface. This difference of air speeds above and below the wings, in accordance with Bernoulli’s principle, creates a pressure difference, due to which an upward force called ‘dynamic lift’ (= pressure difference × area of wing) acts on the plane. If this force becomes greater than the weight of the plane, the plane will rise up. [Working of an Aeroplane]
(iii)Action of atomiser:The action of carburetor, paint-gun, scent-spray or insect-sprayer is based on Bernoulli’s principle. In all these, by means of motion of a piston P in a cylinder C, high speed air is passed over a tube T dipped in liquid L to be sprayed. High speed air creates low pressure over the tube due to which liquid (paint, scent, insecticide or petrol) rises in it and is then blown off in very small droplets with expelled air. [Action of Atomiser]
(iv)Blowing off roofs by wind storms:During a tornado or hurricane, when a high speed wind blows over a straw or tin roof, it creates a low pressure (P) in accordance with Bernoulli’s principle. [Blowing off roofs by wind storms] However, the pressure below the roof (i.e., inside the room) is still atmospheric (= Pₒ). So due to this difference of pressure the roof is lifted up and is then blown off by the wind.
(v)Magnus effect:When a spinning ball is thrown, it deviates from its usual path in flight. This effect is called Magnus effect and plays as important role in tennis, cricket and soccer, etc. as by applying appropriate spin the moving ball can be made to curve in any desired direction.
