This lesson introduces students to the concept of air pressure. Students will explore how air pressure creates force on an object. They will study the relationship between air pressure and the velocity of moving air.

In designing airplanes, trains, cars, rockets and bicycles — nearly everything that moves through the air — engineers must understand Bernoulli's principle. The forces caused by moving air enable an airplane to fly or a train to slow. Understanding how Bernoulli's principle works enables engineers to take advantage of the nature of air pressure so their designs of these and many other applications function correctly, efficiently and safely. airplanes air pressure Bernoulli force fluids Students should be able to: Understand the history of flight (basic facts about). Explain Bernoulli's Principle. Understand the concept of air pressure and how the movement of air influences its pressure. Understand why engineers need to know about air pressure. Ask the students "what is air"? (Answer: Air is a collection of molecules — very small particles that we cannot see — that cover the surface of the Earth. Air is comprised of 78% Nitrogen, 21% Oxygen, and the remaining 1% is mostly argon and carbon dioxide.) Have the students blow onto their hand. (This is air being forced out of their lungs and hitting their hand). Ask them why air does not escape out into space? (Answer: Gravity pulls on air just like it pulls on a person and objects.) The weight of air is called air pressure and it pushes on us all the time. Air pressure is what allows airplanes to fly. From the earliest times, humans have marveled at the flight of birds and have wanted to fly just as they do. According to Greek myth, Icarus flew too close to the sun on wings made of wax, and he fell to his death. Many thousands of years later, it took a series of engineers to make this human dream of flight become a reality. In his lifetime, Leonardo da Vinci (1452-1519), like other inventors of his time, had a fascination with the flapping flight of birds. He believed that "a bird is an instrument working according to a mathematical law. It lies within the power of man to make this instrument with all of its motions." He designed several ornithopters, which are airplanes with flapping wings. He also designed a glider that resembles modern day hang-gliders. In 1738, an Italian physicist named Daniel Bernoulli discovered that water and air move faster over curved surfaces than they do over flat ones. He also discovered that as the air or water moved faster, the pressure exerted by the fluid decreased. This critical discovery, known as Bernoulli's Principle, paved the way for modern airplanes. In 1903, a pair of bike shop owners from Ohio made the world's first powered flight at Kitty Hawk in North Carolina. Orville and Wilbur Wright had studied prior attempts to fly and realized that birds keep their balance by twisting their wings. In 1895, Wilbur designed a kite that reproduced this effect mechanically. Then, for several years after his kite invention, the two brothers experimented with flight using gliders. Wilbur also discovered the principle of combining rudder control with roll for smoother turns. The atmosphere is a sea of air that is about 80 kilometers thick surrounding our planet. All of that air piled on top of us is pulled down by gravity. In fact, the air pushes against us in all directions. This is air pressure. Air is pushing on all people and objects with a force of 14.7 pounds per square inch at sea level. (Disclaimer: With the metric system, pressure is measured in Newtons per square meter, which is called a Pascal. With younger kids, it is easy to use pounds per square inch since the units are more familiar and the numbers are more reasonable. To convert pounds per square inch into Pascals, multiply by 6,895.) As you go higher in elevation, there is less air pushing down, so there is less pressure. The change is not that great until you get very high. Heating the air, cooling it, or causing it to move can change the air's pressure. It is these differences in air pressure that create wind, and make flight possible. Bernoulli discovered that the faster water moves over a surface the lower the pressure the water exerts on that surface. In the diagram below, water flowing out of a bottle moves faster through the neck than it does in the rest of the bottle. Bernoulli proved that the water pressure on the sides of the neck of the bottle were less than those on the sides of the rest of the bottle. Bernoulli then found that these same principles apply to air as well. Bernoulli's Principle simply states that the faster a fluid moves over a surface, the less it pushes on the surface. Engineers use Bernoulli's Principle when designing and testing airplane wings. They can use this information to determine the amount of lift a wing will produce (how high an airplane can go). Engineers also use their knowledge of these principles for other projects relating to fluid flow. We will learn more about how Bernoulli's Principle is related to flight in Lesson 2 of the Airplanes unit. The force exerted by air on an area (metric: N/m2, English: lbs/in2). The law that pressure exerted by a fluid decreases as the rate of flow increases. A push or pull on an object. The force resulting from the difference in air pressure above and below the wings that causes the aircraft to move upwards. Any substance where the molecules can move around feely. A fluid is any gas or liquid. Fun with Bernoulli Air Pressure Ask students to explain air pressure. Then have them explain why one of the Bernoulli's Principle activities they did worked in terms of air pressure. Make sure they understand Bernoulli's Principle (as fluid velocity increases the pressure decreases). As a challenge, ask them "what is a vacuum?" (Answer: A vacuum is a volume with no air in it and therefore no air pressure). Discussion Questions: Solicit, integrate, and summarize student responses. What is air? (Answer: Air is a collection of molecules — very small particles that we cannot see — that cover the surface of the Earth. Air is comprised of 78% Nitrogen, 21% Oxygen, and the remaining 1% is mostly argon and carbon dioxide.) Why doesn't air escape into space? (Answer: Gravity) Why don't you feel the air pressure? (Answer: Your body pushes out against the air to balance the air pressure.) Voting: Ask a true/false question and have students vote by holding thumbs up for true and thumbs down for false. Count the votes, and write the totals on the board. Give the right answer. True or False? Air pressure is caused by the rotation of the Earth. (Answer: False. Air pressure is caused by gravity pulling air towards the Earth.) True or False? The faster air moves, the higher the pressure. (Answer: False. Pressure decreases as air velocity increases.) True of False? Air pressure pushes in all directions. (Answer: True. Air pressure not only pushes down on us, but it also pushes from the sides and even from below.) Bingo: Provide each student with a sheet of paper containing a list of the lesson vocabulary terms. Have each student walk around the room and find a student who can define one vocabulary term. Students must find a different student for each word. When a student has all terms completed s/he shouts "Bingo!" Continue until two or three students have bingo. Ask the students who shouted "Bingo!" to give definitions of the vocabulary terms. Students can research through the library or Internet to learn more about the Bernoulli Principle. There are many web sites to explore the subject of air pressure and the Bernoulli Principle, such as: http://www.physicsmyths.org.uk/bernoulli.htm and http://library.thinkquest.org/3142/lift.htm. Hixson, B. K. Bernoulli's Book. The Wild Goose Co. Salt Lake City, Utah. 1991. http://www.sciencejoywagon.com/physicszone/lesson/02forces.htm http://www.thinkquest.org/library/lib/site_sum_outside.html?tname=27948&url=27948/bernoulli.html