TIPS GUIDE Physics EN
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The document describes several experiments that can be done to teach students about the key principles of flight, including Bernoulli's principle, the Coanda effect, and the Venturi effect. It explains three activities: 1) using thread to visualize air flow and how it curves around surfaces, 2) experiments with paper to demonstrate Bernoulli's principle, and 3) building a paper airplane to demonstrate lift. Diagrams and formulas are provided. The summary concludes that these principles allow airplanes and birds to fly and were important to the development of aviation technology.
TIPS GUIDE Physics EN
- 1. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein. Teaching Innovative Practices in STEM (TIPS) 2015-1-ES01-KA219-015719_1 Teaching Innovative Practices in STEM TIPS – Physics 1. Abstract This TIPS guide focuses on the experimental observation of some key phenomena which are the foundation of the technological developments achieved by modern aviation. The theme of the flight, of its history and of the steps towards its accomplishments is suitable for a cross-curricular approach involving science also under a historical and cultural point of view and has its roots in Leonardo da Vinci’s work. In order to arouse the students’ interest and to let them understand the principles underlying the flight in all its forms – from the birds’ flying to the flight of modern airplanes – we can suggest some easy lab activities which can become the starting point of a theoretical study based on Bernoulli’s principles. 2. Materials and procedures Activity N. 1: - The barrel of a ballpoint pen (or a straw ) - Sewing thread - tape - a cylindrical glass (or a bottle, a can, etc) Activity N. 2: - A4 paper sheets Activity N. 3: - A4 paper sheet with the drawing of the paper airplane to cut out 1) Coandă Effect – how to visualize air flow Materials needed - the barrel of a ballpoint pen (or a straw ) - sewing thread - tape - a cylindrical glass (or a bottle, a can, etc…) Instructions - insert the thread into the barrel (you can suck it up, without swallowing it!) -fix the thread outside the barrel with some tape -when you blow, the thread highlights the outcoming flow of air and takes a horizontal position. Observation - when the air flow finds a curved surface, for example the one of a glass or a bottle, it follows it. So, the air flow curves downwards when we get the glass closer up from down, while it curves upwards when we get the glass closer down from up. 2) Simple experiments to study the Bernoulli Principle a) Keep two thin pieces of paper vertically at a close distance one from the other and blow downwards into the space between them. You can notice that the two sheets get closer to each other. b) Keep one edge of a small paper sheet with both hands. Keep the edge horizontal and blow steadily over the top part of this horizontal edge. Here you can notice that it lifts, since the air pressure on the top surface is lower than the one on the bottom surface. 3) Studying the Bernoulli Principle with a paper airplane (http://weirdsciencekids.com/paperairplane.html) We can build a special paper airplane to demonstrate how and why airplanes and most birds can fly (without using an engine or wings).
- 2. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein. Teaching Innovative Practices in STEM (TIPS) 2015-1-ES01-KA219-015719_1 Fig. 1 Instructions 1) Cut out the outline of the airplane along the bold printed line. Then, fold the top part along the dotted line so that it corresponds with the bottom half. Fold so that the two ends form a drop- shaped form. 2) Put a small piece of tape at the extremities of the wings and in the middle on the points marked A, B and C. Now fold the plane along the central line so as to create a flat ‘V’. The angle of the 'V' should be no more than about 15 degrees. Execution of the experiment Let the plane hover and regulate its stability. To avoid that the top part of the airplane pulls up to a deadlock add a small weight close to the top (point D), a paper clip or two, for example. It is also possible to regulate the movement of the airplane along its lateral and/or longitudinal axis by making small cuts into the tail and the wings, folding the paper into the cutouts up or down, as if they were a rudder or ailerons. Explanation Bernoulli Law allows to explain how air keeps airplanes up. This phenomenon is called lift and is connected to the Venturi Effect, which takes its name from the Italian physicist Giovanni Battista Venturi, who lived between the 18th and the 19th century. When the speed of a fluid increases, its pressure decreases and vice versa. Therefore airplanes are designed so that the air moves faster above the wings, thus generating a pressure difference which can keep aircrafts up. For a given wing profile, by bending the upper part of the profile, the air moving above the profile will have to cover a longer distance as compared with the air below, forcing the air to move faster. The result is: less pressure on the top part and more pressure on the bottom part (lift). Air pressure below the wing pushes the wing up from down. FORMULAS BERNOULLI LAW Bernoulli equation with reference to the paper sheets is the following: Pi + 1 2 d ui 2 = ps + 1 2 d us 2 where: - pi stands for air pressure on the bottom face of the sheet - d stands for the density of the fluid - ui stands for air speed on the bottom face - ps stands for air pressure on the top face - us stands for air speed on the top face If A is the area of the sheet, the force applied on the face of the sheet is equivalent to: F= A · ( pi – ps ) Drawing of the paper airplane to cut out
- 3. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein. Teaching Innovative Practices in STEM (TIPS) 2015-1-ES01-KA219-015719_1 Since air speed on the top face of the sheet is higher than the speed on the bottom face, air pressure on the sheet is less than the one under the sheet. The pressure difference creates a force directed upwards which lifts the sheet. A similar example refers to the wing of an airplane. The shape of the wing is designed so that by flying the air moves faster on the top surface than on the bottom one. Like in the case of the paper sheet, a pressure difference is created and consequently a resulting vertical force pushing the wing upwards. COANDĂ EFFECT Coandă Effect is the tendency of the flow of a flu- id to follow the outline of a nearby surface. This phenomenon takes its name from the Romanian pioneer of aerodynamics Henri Coandă, who in 1936 patented first in France and later in the USA some tools which exploited the capability to di- vert a flow. When the fluid moves along the surface, this one creates air resistance, which tends to make it slow down. However, the resistance to the movement of the fluid is applied only to the particles of the fluid which are immediately in contact with the surface. Due to the molecular interactions which tend to keep the external particles of fluid close to the internal ones, the former ones will change direction towards the latter ones because of the difference in speed, therefore causing the fluid to adhere to the same surface. Example of the spoon: By getting a spoon close enough to a water flow, the flow will be diverted towards the surface of the spoon: in fact, if a water stream runs along a solid surface which is slightly curved ( convex ) , the water tends to follow this surface. By keeping the spoon so that it can swing, we can feel clearly how it is attracted towards the flow. The same example is presented in activity N. 1 VENTURI EFFECT Fig. 3 Venturi Effect (or hydrodynamic paradox ) is the physical phenomenon discovered and studied by the Italian physicist Giovanni Battista Venturi, according to which the pressure of a fluid flow, air included, increases as speed decreases. From the figure we can see that by increasing air speed from right to left the pressure in the tubule on the right is higher than in the one on the left. Fig. 2 The figure shows the experiment of the spoon. If we let a small river of water flow along the convex side of the spoon we can notice that the water won’t fall vertically but it will adhere to the side of the spoon. Figure 3 shows the experiment about the Venturi Effect. Take a horizontal glass tube with a narrowing, that is with two different diameters, connected to a capillary U-tube in which is poured some liquid (water). If we let air flow into the horizontal tube from the larger part to the narrower part we can notice that air speed in the narrower part increases, but at the same time the level of water in the tubule rises, that is air pressure decreases. AIR LOW PRESSURE DIFFERENCE IN PRESSURE
- 4. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein. Teaching Innovative Practices in STEM (TIPS) 2015-1-ES01-KA219-015719_1 The same effect can be observed in a tube in which the middle part is narrower. This experiment confirms Bernoulli Law p+1/2 d v2 = constant with d density, p pressure and v speed of the flow. Therefore we can notice that as the speed of the fluid increases, a decrease of the internal pressure in the fluid is necessarily created. Venturi Effect is also called hydrodynamic paradox, since we might think that the pressure increases at the narrowings; however, following the Law of the Flow Rate, at the narrowings it is the speed which increases. Therefore, considering a tube which ends into a plate as in figure 5, if the fluid has a slightly higher pressure than the pressure of the atmosphere, the increase in speed created by the narrowing between the tube and the plate will cause an increase in speed at the expense of the pressure of the fluid. If the pressure gets lower than the pressure of the atmosphere, the plate will tend to close the tube instead of flying away. This is the origin of the hydrodynamic paradox, which is a consequence of Bernoulli Law. 3. Results The three activities and the three laws above mentioned are the foundations of the theory of flight. Airplanes, both engine-driven and not, make use of the physical consequences of Bernoulli Law, Coandă Effect and Venturi Effect to leave the ground. Some studies aim at using Coandă Effect to develop aircrafts with particular profiles and the advantage of better maneuverability and the abil- ity of spinning in the air. Fig. 4 Figure 4 shows the same experiment as Figure 3. The speed of the fluid in the narrow part is higher (position 2) and as we can see from the upper tubule, the pressure is lower as compared with the tubule which is in the larger part. A1 is the larger section of the tube and A2 is the narrower section of the tube. h is the height of the water level and Δh is the difference in height, that is the difference in pressure. Fig. 5 The figure shows that if at the end of a tube there is a plate, the last one will not be thrusted away by the air flowing along the vertical tube, but if the pressure of the air is slightly lower than the pressure of the atmosphere, the plate will close the tube hermetically.
- 5. The European Commission support for the production of this publication does not constitute an endorsement of the contents which reflects the views only of the authors, and the Commission cannot be held responsible for any use which may be made of the information contained therein. Teaching Innovative Practices in STEM (TIPS) 2015-1-ES01-KA219-015719_1 It was used in Formula 1 races for some years until 2013 through particular forms of car bodies which could direct the flow of hot air coming out of the side exhaust pipes at the back of the car, creating a sort of aerodynamic ‘ seal ‘ useful to in- crease the efficiency of the extractor itself and so the aerodynamic load. The considerable study of aeronautical engineer- ing lies in the form and in the width of the wing so as to allow the application of these effects and laws. These simple activities aimed at illustrating the main physical laws which guide the study of the three principal forces that allow an airplane to fly: lift, thrust and drag. Fig.8 The figure shows how air behaves when it finds objects with different shapes. THRUST AND DRAG 4. References www.google.com/immagini www.It.m.wikipedia.org http://www.machaurora.it/teoria/ http://weirdsciencekids.com/paperairplane.html www.reinventore.it Fig. 6 The modification of the wing profile allows the air- plane to rise or fall. Fig. 9 The figure shows the 4 forces involved in the flight of an airplane. Fig. 7 The figure shows the concept of lift BACK air flow LIFT BOTTOM Sphere Spherical bodies are subject to average resistance Aerodynamic surface The shape of the wing of an aircraft makes air resistance low Square surface For bodies with sharp edges resistance is high