Principles of Flight: Bernoulli’s Principle – NASA

ing of flight, it is important to understand the forces of flight (lift, weight, drag, and thrust), the First, it takes thrust to get the airplane moving – Newton’s first law.
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2 Bernoulli™s Principle Lesson Overview In this lesson, students will learn about forces and motion as they see how the work of Daniel Bernoulli and Sir Isaac Newton help explain ˜ight. Students will also learn how lift and gravity, two of the four forces of ˜ight, act on an airplane while it is in the air. Additionally, students will experiment with the Bernoulli Principle. Students will relate the Bernoulli Principle to lift. Finally, students will relate the Bernoulli Principle to lift and apply the ˚rst and third laws of Sir Isaac Newton to ˜ight. Objectives Students will: 1. Explore the Bernoulli Principle, which states that the speed of a ˜uid (air, in this case) determines the amount of pressure that a ˜uid can exert. Determine that though two items look identical, they may not have the same density. 2. Relate the Bernoulli Principle to the lift, one of the four forces of ˜ight. 3. Explore, within the context of the Bernoulli Principle activities, how Newton™s ˚rst and third laws of motion contribute to ˜ight. Materials: In the Box Large paper grocery bag Scissors Tape or glue stick Ruler Variety of balloon shapes (optional) 2 large balloons 2 lengths of string 30cm each Straight straw (optional) 1 large trash bag 1 hair dryer or small fan with at least two speeds 1 ping-pong ball Provided by User Paper Assortment of large felt tip markers (washable) GRADES K-4 Time Requirements: 3 hours

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3Background How is it that today™s airplanes, some of which have a maximum take o˛ weight of a million pounds or more, are able to get o˛ the ground in the ˚rst place, let alone ˜y between continents? Surprisingly, with today™s technological advances, airplanes use the same principles of aerodynamics used by the Wright brothers in 1903. In order to gain an understand -ing of ˜ight, it is important to understand the forces of ˜ight (lift, weight, drag, and thrust), the Bernoulli Principle, and Newton™s ˚rst and third laws of motion. Although the activities in this lesson primarily focus on the role the Bernoulli Principle plays in the ability of aircraft to achieve lift, the Bernoulli Principle is not the only reason for ˜ight. The Forces of Flight At any given time, there are four forces acting upon an aircraft. These forces are lift, weight (or gravity), drag and thrust. Lift is the key aerodynamic force that keeps objects in the air. It is the force that opposes weight; thus, lift helps to keep an aircraft in the air. Weight is the force that works vertically by pulling all objects, including aircraft, toward the center of the Earth. In order to fly an aircraft, something (lift) needs to press it in the opposite direction of gravity. The weight of an object controls how strong the pressure (lift) will need to be. Lift is that pressure. Drag is a mechanical force generated by the interaction and contract of a solid body, such as an airplane, with a fluid (liquid or gas). Finally, the thrust is the force that is generated by the engines of an aircraft in order for the aircraft to move forward.Lift Drag Thrust Weight Fig. 1 Four forces of ˜ight Newton™s Laws of MotionAnother essential that applies to understanding how airplanes fly are the laws of motion described by Sir Isaac Newton. Newton (1642 -1727) was an English physicist, mathematician, astronomer, alchemist, theologian and natural philosopher. He has long been considered one of the most influential men in human history. In 1687, Newton published the book ﬁPhilosophiae Naturalis Principia Mathematicaﬂ, commonly known as the ﬁPrincipiaﬂ. In ﬁPrincipiaﬂ, Newton explained the three laws of motion. Newton™s first and third laws of motion are especially helpful in explaining the phenomenon of flight. The first law states that an object at rest remains at rest while an object in motion remains in motion, unless acted upon by an external force. Newton™s second law states that force is equal to the change in momentum per change in time. For constant mass, force equals mass times acceleration or F=m·a. Newton™s third law states that for every action, there is an equal and opposite reaction.Img. 1 Sir Isaac Newton (age 46) (Painting by Sir Godfrey Kneller – 1689)

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4The Bernoulli PrincipleDaniel Bernoulli (1700 Œ 1782) was a Dutch-born scientist who studied in Italy and eventually settled in Switzerland. Born into a family of renowned mathematicians, his father, Johann Bernoulli, was one of the early developers of calculus and his uncle Jacob Bernoulli, was the first to discover the theory of probability. Although brilliant, Johann Bernoulli was both ambitious for his son Daniel and jealous of his son™s success. Johann insisted that Daniel study business and later medicine, which Daniel did with distinction. It was mathematics, however, that really captured Daniel™s interest and imagination. Despite Daniel™s best efforts, Johann never acknowledged his son™s brilliance and even tried to take credit for some of Daniel™s most important ideas.After Daniel™s studies, he moved to Venice where he worked on mathematics and practical medicine. In 1724, he published Mathematical exercises, and in 1725 he designed an hourglass that won him the prize of the Paris Academy, his first of ten. As a result of his growing fame as a mathematician, Daniel was invited to St. Petersburg to continue his research. Although Daniel was not happy in St. Petersburg, it was there that he wrote ﬁHydrodynamicaﬂ, the work for which he is best known. Bernoulli built his work off of that of Newton. In 1738, he published ﬁHydrodynamicaﬂ, his study in fluid dynamics, or the study of how fluids behave when they are in motion. Air, like water, is a fluid; however, unlike water, which is a liquid, air is a gaseous substance. Air is considered a fluid because it flows and can take on different shapes. Bernoulli asserted in ﬁHydrodynamicaﬂ that as a fluid moves faster, it produces less pressure, and conversely, slower moving fluids produce greater pressure. Img. 2 Daniel Bernoulli (Public Domain) hpV1P1A112V2P2A2Fig. 2 Bernoulli ˜uid experiment We are able to explain how lift is generated for an airplane by gaining an understanding of the forces at work on an airplane and what principles guide those forces. First, it takes thrust to get the airplane moving – Newton™s first law at work. This law states that an object at rest remains at rest while an object in motion remains in motion, unless acted upon by an external force.

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5 Then because of the shape of an airplane™s wing, called an airfoil, the air into which the airplane flies is split at the wing™s leading edge, passing above and below the wing at different speeds so that the air will reach the same endpoint along the trailing edge of the wing at the same time. In general, the wing™s upper surface is curved so that the air rushing over the top of the wing speeds up and stretches out, which decreases the air pressure above the wing. In contrast, the air flowing below the wing moves in a straighter line, thus its speed and pressure remain about the same. Since high pressure always moves toward low pressure, the air below the wing pushes upward toward the air above the wing. The wing, in the middle, is then ﬁliftedﬂ by the force of the air perpendicular to the wing. The faster an airplane moves, the more lift there is. When the force of lift is greater than the force of gravity, the airplane is able to fly, and because of thrust, the airplane is able to move forward in flight. According to Newton™s third law of motion, the action of the wings moving through the air creates lift. Trailing Edge Leading Edge Fig. 3 Airfoil

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6 Activity 1 Bernoulli and the Paper Bag Mask GRADES K-4 Time Requirements: 45 minutes Materials: Note to the Teacher: Decide if you are going to present this activity as a demonstration or as a hands-on learning experience for the whole class. For a demonstration, you will only need one of each item. For a hands-on class activity, you will need one set of the materials for every two students so that your students may work in pairs. In the Box Large paper grocery bag Scissors Tape or glue stick RulerVariety of balloon shapes (optional)Provided by User Paper Assortment of large felt tip markers (washable) Worksheets Bernoulli Experiment Log (Worksheet 1) Student Activity Directions (Worksheet 2) Reference Materials NoneObjective: Students will learn about the position and motion of objects as they: 1. Create a paper bag mask to experiment with the Bernoulli Principle. 2. Explain how the Bernoulli Principle applies t o the movement of the paper tongue attached to the paper bag mask. 3. Explain how the phenomenon they experienced in the paper bag mask activit y relates to ˜ight (lift). 4. Understand the e˛ect of air ˜owing over a cur ved surface. Activity O verview: Students will make a paper bag mask with a protruding paper tongue, which they will use to experiment with the Bernoulli Principle. The students will be able to explain the Bernoulli Principle after they have observed it in action during the experiment. Activity : 1. If all of your students are going to participate in this activity, have the directions for the activity written on the board or make a copy of the direction sheet for each student or pair of students. 2. Ask the students this question: How do airplanes, some of which weigh a million pounds, ˜y? Students™ responses will v ary but look for and encourage a response that includes weight or gravity. Tell the students that in order to ˜y, airplanes must overcome gravity, a force that wants to keep the airplane on the ground. 3. Explain to the students that in order to overcome gravity, airplanes have to achieve lift, a force that opposes (or pushes against) gravity. The greater the weight of the airplane, the greater the lift required. 4. Explain to the students that today they will learn about a scienti˜c principle that will help them understand lift. Tell the students that the principle is called the Bernoulli Principle; it is named after the man who discovered it. (Here you can give the students some simple background information about Daniel Bernoulli. You may also show the students his picture.) Key Terms: Air pressure Air f oilBer noulli Principle Fluid For ce Gra vity Lift

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89. Next, cut a mouth-shaped hole approximately 2 inches in height at the widest point, the middle, of the mouth. Have the students use safety scissors for this portion of the activity or have additional adults in the room to supervise. 10. To make the tongue, cut a strip of printer/ copier paper approximately 1½ inches wide and 8 inches long. 11. Fold down one end of the tongue to create a ¼ inch tab. Tape or glue the tab to the inside of the bag along the lower middle edge of the mouth. The rest of the tongue should be hanging out of the mouth. 12. Place the bag over a student™s head and instruct the student to blow through the mouth hole with an even stream of air while the rest of the students observe the movement of the tongue. (If this is being done in pairs, the partner who is not wearing the bag will do the observing.) Have the student wearing the bag vary the strength with which he or she blows. Remind students to keep a steady ˜ow of air and to not just give a quick burst of air. Students will compare the e˛ect of a gentle blow to the e˛ect of a harder blow. If students are working in pairs, have them take turns wearing the bag and observing. (Students will notice that a gently blown stream of air will cause the tongue to rise, but a more forcefully blown stream of air will not lift the tongue at all.) 13. Students record their observations on the Bernoulli Experiment Log.

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914. After the experiment, show a diagram of the cross-section of an airplane wing (also called an airfoil). Trailing Edge Leading Edge 15. Tell the students that the wing of an airplane is shaped in order to control the speed and pressure of the air ˚owing around it. Air moving over the curved upper surface of the wing will travel faster and thus produce less pressure than the slower air moving across the ˜atter underside of the wing. This di˛erence in pressure creates lift which is a force of ˜ight that is caused by the imbalance of high and low pressures. 16. Relate this information to the paper bag mask by saying this: Another example of Bernoulli™s Principle was seen in our paper bag mask(s). When the air we blew over the curved surface of the paper tongue was faster than the air under the tongue, the unequal air pressure lifted the tongue in the same way an airplane wing produces lift. Fig. 3 Airfoil

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11 Activity 2 Balloon Magic GRADES K-4 Time Requirements: 60 minutes Materials: Note to the Teacher: Decide if you are going to present this activity as a demonstration or as a hands-on learning experience for the whole class. For a demonstration, you will only need one of each item. For a hands-on class activity, you will need one set of the materials for every two students so that your students may work in pairs. In the Box 2 large balloons 2 lengths of string 30cm eachStraight straw (optional) 1 large trash bag Provided by User NoneWorksheets Bernoulli Experiment Log (Worksheet 1) Student Activity Directions (Worksheet 2) Reference Materials NoneObjective: Students will learn about the position and motion of objects as they experiment with the Bernoulli Principle using a pair of in˜ated balloons that are suspended at the same height though several inches apart. By blowing air directly between the balloons, students will demonstrate the Bernoulli Principle and then explain the phenomenon to their classmates. Activity Overview: In this activity, students will experiment with the speed of the air˜ow between two suspended balloons, observing how fast moving air creates an area of low pressure and how high pressure moves toward low pressure. Activit y: 1. Review what the students have learned so far about the Bernoulli Principle. Faster mo ving air equals less air pressure than slower moving air. Also re view what the students have learned so far about lift. Lift is the forc e that opposes gravity and helps an airplane to ˜y. Lift is achieved in part by the design of an airplane™s wing. Air moves more quickly over the curved upper surface of the wing than it does under the wing, which has a ˜atter surface. The faster moving air produces less pressure than the slower moving air, causing the wing to lift toward the area of low pressure. 2. Now tell the students that they will explore the Bernoulli Principle again, but this time the activity will involve balloons. If you are going to allow pairs of students (3rd and 4th grade) to construct their own experiment, caution the students about over-in˜ating the balloons.

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