LESSON Understanding. Bernoulli s principle. Bernoulli s principle. Activities to show Bernoulli s Principle

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1 idang sains dan matematik LESSON pplication ernoulli Principal LESSON Understanding ernoulli s principle. ernoulli s principle. ernoulli s principle states that The pressure of a moving liquid decreases as the speed of the fluid increases and vice versa. ctivities to show ernoulli s Principle ctivity 1 The conditions which enable the errnoulli s Principle to use (1) The fluid is incompressible and flows easily (2) The fluid is streamline or in layers,i.e. there are no eddies or turbulence Factors affecting the speed of the moving liquid. (1) The speed of moving object increases as the area of moving fluid decreases (2) The speed of moving object increases as the distance of moving fluid ernoulli s principle and the law of conservation of energy Energy is always conserved and this also applies to fluids, wether static or in motion. fluid in motion has kinetic energy. This kinetic energy imparted to the fluid comes at the expense of the pressure of the fluid. Thus, when the speed (kinetic energy) of the fluid increases, its pressure decreases. When the air is blown up in the surface of a piece of paper,its observed that the paper moves up. This happened because the air moved at a very high velocity. ccording to ernoulli s Principle, the pressure of the moving air decreases as the speed of the air increases. The higher atmospheric pressure which acts at the bottom of the paper pushes up the paper. ctivity 2 When the air is blown harder through the straw, The two ping-pong balls will move closely to each other. The air moved at a very high velocity between the balls. ccording to ernoulli s Principle, the pressure of the moving air decreases as the speed of the air increases. The higher atmospheric pressure caused the pingpong balls closer to each other. 1

2 idang sains dan matematik LESSON pplication ernoulli Principal ctivity 3 When the air blows harder,the ball is not falling down. It is because the air moved at a very high velocity between the balls and the wall of the filter tunnel. ccording to ernoulli s Principle, the pressure of the moving air decreases as the speed of the air increases. The bottom of the ball has the higher atmospheric pressure which can hold the ball from falling down. ctivity 4- Using Venturi tubes Mark the water level in the vertical tubes P,Q and R in the following figures. Use of ernoulli s Principle in Everyday Life (1) person who stands near a railway feels like falling into it when suddenly a train moves with a high speed passes him. It is because the velocity of the air in front of him increases. ccording to ernoulli s Principle, the pressure of the moving air decreases as the speed of the air increases. The higher atmospheric pressure behind pushes him forward. (2) When two speed bots move faster and closely to each other, an accident may be occurred. It is because the water moved at a very high velocity between the boats. ccording to ernoulli s Principle, the pressure of the moving air decreases as the speed of the air increases. The higher water pressure on either sides of the boats caused its closer to each other. (3) table-tennis player often gives the ball top spin enabling a hard drive to be hit over the net and land on the table. ball hit with spin swerves considerably in its path. 2

3 idang sains dan matematik LESSON pplication ernoulli Principal (2) Insect Piston Spray The figure above shows the rotating surface of the ball, due to spin, and v the air velocity. The spin of the ball carry some air with it, and the resultant velocity of air on the upper surface will therefore be less than v, and the lower surface greater than v. There is therefore a pressure difference between the upper and lower surfaces which deflects the ball, originally hit from right to left in downwards direction Use of ernoulli s Principle in When the piston is pushed, air is forced out through the jet of gas at a high speed. ccording to ernoulli s Principle, the pressure of the moving air decreases as the speed of the air increases. The higher atmospheric pressure in the insect poison container will push the insect poison liquid up through the narrow metallic tube. (3) Filter pump (1) unsen burner When the jet of gas flows out from the nozzle with high velocity, the pressure in the unsen burner becomes low(ernoulli s principle) higher external atmospheric pressure will be sucked into the air hole and be mixed with the gas. The mixture of gas and air allows more complete combustion of the gas. Water from a tap flows at high speed out of the jet of water(nozzle). ccording to ernoulli s Principle, the pressure of the moving air decreases as the speed of the air increases The higher air ssure in the vessel pumps air from the side tube to which the vessel is connected. 3

4 idang sains dan matematik LESSON pplication ernoulli Principal (4) arburettor TUTORIL 6 1 The figure shows two polystyrene spheres are hung by a string respectively. When the air is blown harder through the straw, the balls will When the engine is switched on, air is sucked into the the venture tube. Fast moving air in the narrow section of the tube causes a low pressure at this region. The higher atmospheric pressure in the petrol compartment will push the petrol into the region. The petrol will mix with air before it flows into the cylinder engine for combustion. remain stationary move closely to each other move far apart to each other 2 The figure shows the flow a liquid through a ernoulli tube. The smallest pressure of the liquid is at point (5) erofoil 3 The figure shows water flows through a Venturi tubes from point P to point Q. In which vertical tubes,, or the pressure of water is very low? The above figure shows the streamlines round a thin wing at an angle of attack to the air stream. It will be seen that the path of air is longer over the upper surface than the lower, and therefore the speed is greater on the upper surface. The lift is produced by the difference in pressure between the two surfaces, which helps the plane to take-off. In addition to its use in airplanes, aerofoil is also used in racing cars. In this case, the downward force helps to stabilize the car at high speeds. 4 The figure shows an arrangement of apparatus which is used to show the ernoulli s Principle. When the air is blown, the level of water in tube 4

5 idang sains dan matematik LESSON pplication ernoulli Principal X will the highest Y will the highest Z will the highest X,Y and Z will the same 5 The figure shows water rising up the tubes X,Y and Z if the air is blown. 7 Which of the following is based on ernoulli s Principle? Syringe rinking straw unsen burner 8 The figure shows a water spray that is produced when the air flows through the jet. Which of the following is true regarding the water level in tube X,Y and Z? Water level in X < Water level in Y < Water level in Z Water level in X < Water level in Z < Water level in Y Water level in Z < Water level in Y < Water level in X Water level in Y < Water level in Z < Water level in X 6 The figure shows the wing of an aeroplane which is moving with a uniform acceleration in the direction shown by the arrow. Which of the following is true? ccording to Pascal s Principle,the that above system produces a water spray. The air pressure at Q is higher than that at P The velocity of air at Q is higher than that at P 9 The figure shows a motion a ball when it is kicked by a player. Which of the following is true? The uplift force is higher than the weight of object The resultant force in direction of the motion of the object is zero The pressure in region P is higher than in region Q The velocity of air in region P is higher than in region Q. The motion of the ball can be explained by Principle of conservation of momentum Principle of conservation of energy rchimedes principle ernoulli s principle 10 ball which is thrown forward in a spin moves in a curve, as shown in the figure. 5

6 idang sains dan matematik LESSON pplication ernoulli Principal tube X until water reaches level. The curved path taken by the ball is due to equilibrium of forces ernoulli s principle rchimedes principle principle of conservation of momentum Figure(a) 11 The figure shows a ping-pong ball that does not fall when the water flows. (a) (i) Mark on the Figure(a),the possible water levels for tube Y and Z. (ii) alculate the pressure at P exerted by the column of water if is 10 cm height from P. [ ensity of water = 1000 kg m -3 ] Which principle explains the figure? Pascal s principle ernoulli s principle rchimedes principle 12 Which of the following instruments is not based on ernoulli s principle? (iii) If the cross sectional area of tube X is 2 x 10-5 m 2, calculate the force acted by by the column of water in tube X. Filter pump ar carburetor Rubber plunger Wing of aeroplane 12 Figure(a) shows a horizontal tube both ends closed with rubber stoppers is fixed with three vertical tubes X,Y and Z. Water is poured into Figure(b) shows the rubber stoppers at both ends of tube are taken away so that the water can flow uniformly from end to end, then water water tube X rises until level. 6

7 idang sains dan matematik LESSON pplication ernoulli Principal 13 Figure(a) shows a cross section of the wing of an aeroplane. The slat and the flat can be moved during flying. Figure (b) (b) (i) Mark on the Figure(b),the possible water levels for yube Y and tube Z. (ii) Give one reason for your answer in b(i) Figure(c) shows the apparatus is modified so that the middle part of the horizontal tube becomes narrow. Water slows uniformly from from end end G to end H of the tube and it is found that the water level of tube X is at E. Figure (c) (c) (i) Mark on the Figure(c), the possible water levels of tube Y and tube Z. (ii) ompare the velocity of water at Q and R. (a) (b) Figure(a) Name the shape of the the wing. Figure(b) Figure(b) shows the cross section of the wing with its flap extended after take-off. (i) Mark the region of high velocity with the letter S. (ii) ased on the Figure(b), explain how the uplift force is produced to help the plane take-off. (iii). What is the relationship between velocity and pressure of water along the horizontal tube GH. (iii) Name the principle involved in(b)(ii). 7

8 idang sains dan matematik LESSON pplication ernoulli Principal (iv) Explain why the surface area of the wing is increased by extends slat and flat after the airplane has taken off. Figure(a) (a) Figure(b) Observe the figures and state the similarities between the positions of the the ping-pong ball and the boats.. (b) (i) State three physical quantities involved to cause the change of the positions of the ping-pong ball and the boats. 14 Figure(a) shows the positions of a ping-pong ball before and after a stream of water from a tap is flown. Figure(b) shows the positions of two toy boats before and after a stream of water from a hose is directed between the boats. (ii) State the relationship between the physical quantities that is stated in b(i) (iii) Name the principle involved in b(ii) (c) If the ping-pong ball is replaced by the metal ball, (i) what will happen to position of the ping pong ball when the tap is opened. (ii). Give a reason for your answer in (c)(i). 8

9 idang sains dan matematik LESSON pplication ernoulli Principal 15 Figure(a) shows a piece of paper hanging from a retort stand. When air flows from the nozzle of an air pump, the paper changes its position as shown in Figure(b). (e) Name the principle that causes the the observations in Figure(b) (f) Name one piece of apparatus in a school laboratory which uses the principle in(e). Figure(a) Figure(b) (a) ompare the position of paper in Figure(a) nd Figure(b).. (b) F is a force that causes the paper to change its position. In box, X, on Figure(b), indicate and label the direction of F that acts on the paper. (c) Explain how F is produced? (d) (i) ompared to the position of the paper in Figure(b), how does the position of the paper change when the air flows faster? (ii) Give a reason for your answer in d(i). 9