By Paul Lupton PhD.
(Provided as a “Take Home” from Teacher Day at EAA Airventure 2010, Oshkosh, WI)
As a retired educator, I am keenly aware of the public outcry against many governmental programs including education. From ignorance of US history, to math, to science, schools are often faulted for failing the grade.
While Aerospace topics are hardly a panacea they do offer to students of all ages an interesting and exciting vehicle to entice young minds with concepts that help unlock the mysteries of flight in the atmosphere and space, and lead minds into real applications of math and science.
Environmental awareness has caught the public’s attention too. Serious students of environmental issues know that solutions involve far more than picking up trash. The solutions always involve biology, chemistry, and physics.
Fortunately, teaching basics of Aerospace intersects in many ways with the knowledge needed to solve larger problems facing scientists (Critical Thinking). Learning about meteorology for pilots opens doors to understanding how pollution can move thousands of miles. Studying how GPS works connects with how GPS can track animal migratory movements. Investigating how air flow causes a wing to lift or how a rocket can propel itself can lead to a discussion of the work of scientists like Isaac Newton who used mathematics to clearly state the laws of motion.
EAA Chapter 1158 in West Bend, Wisconsin has been working with youth since 2000 to not only give them the thrill of flight but to stimulate their thinking to probe deeper into the science and math that has made the wonder of Aerospace achievements possible.
The teaching aids displayed have been chosen to illustrate in simple ways how many basic principles such the Bernoulli Effect, the strength of air pressure, the curious behavior of a gyroscope, and the importance of density in understanding weather mechanics can be exhibited in table top demonstrations.
STUDYING OUR ATMOSPHERE.
A SAMPLE LESSON: THE STRENGTH OF AIR PRESSURE.
OBJECTIVE: STUDENTS WILL BE ABLE TO STATE THE AVERAGE AIR PRESSURE PER SQUARE INCH AT SEA LEVEL AND EXPLAIN WHAT CAUSES IT.
MATERIALS: SOFT FOAM BLOCKS AND A PAIR OF LARGE (about 4 inch diameter) SUCTION CUPS
Introduction: Sitting in our living room the air in the room would appear to be invisible and a sensation of crushing pressure would not be apparent. In the next few minutes you will understand that although air molecules are too small to be seen their presence is very real and they do actually produce enormous pressure on every object in the room! In fact the weight of the air molecules in the average home is several tons! Add to that the fact that the air in the room is only a tiny fraction of the molecules stacked up over our heads reaching over 20 miles into the sky.
For many centuries only four facts about air were known. We could feel its temperature and motion, (cold and windy, for example), the sky contained clouds and storms, and air was necessary for fire. With the Renaissance came a shift in thinking from naive acceptance of “authorities” answers, to experimentation and discovery. Understanding of gases developed but there was no knowledge of the atmosphere as we know it. By climbing a mountain with crude instruments such as a jar that could be sealed and opened at the mountain top, observers began to formulate ideas about the atmosphere. It took centuries before aircraft and rockets could sample the air at very high altitudes. We now know that about 98% of the molecules that compose the atmosphere are found below 100,000 feet or about 20 miles. If a globe model of the earth with about a 1 foot diameter is used for a demonstration, the thickness of the atmosphere would be barely the thickness of 3 or 4 sheets of average paper!
The atmosphere is our friend. Not only is it necessary for plants and animals to utilize the atmosphere to sustain life as we know it, the atmosphere serves as a very efficient (sometimes violent) transport vehicle to distribute heat and water to all parts of the world. It also serves as a protective shell for “Space Ship Earth” shielding us from harmful radiation, cosmic rays, meteorites, insulating us from the freezing temperatures of space, and providing a “hiway” for birds, insects and plant seeds. There is no need to justify our learning about our atmosphere. Without it we wouldn’t be here!
Use about a half dozen soft foam blocks about 1 inch thick and about 4 inches square, Place just one on the demonstration table and show how it can easily be compressed. Place another on top of it and ask the students if the bottom one is compressed. Most will respond no. Continue to add blocks until all are used. Repeat the question. Most will still say no. Repeat the question again by saying: What if instead of 5 blocks, we used 50, or 500, or 5 million?” At some point students will get the idea that eventually the lower blocks will be compressed.
Explain that even though the compression may be invisible to the eye the second block did cause some compression because it had some weight. Air molecules are like the foam blocks but incredibly smaller and they do have some weight. Millions will fit on the head of a pin! Stack them up 20 miles deep and the air pressure at the bottom will be, on average 14.7 lbs per square inch. Because few of us live at sea level the pressure at higher elevations will be lower. Residents of Denver Colorado experience about 10 to 11 pounds per square inch because they live “further up the stack”. Climbers at the top of Mt. Everest may record only 5 or 6 inches on an instrument. Curiously, unless we experience rapid pressure changes, such as going up or down in the elevator of a tall building, or flying in an unpressurized aircraft and make a rapid ascent or decent, there will be little sensation. A notable exception, however, is a person with a head cold that blocks free air movement through a tiny tube connecting the inner ear to our nose and mouth. For those persons the experience could be severe pain to the ear drum and could potentially cause damage.
Using the pair of suction cups show how the lever handle on each cup will cause the rubber cup side to flatten or dish out depending on the position of the lever handle. With the levers in the flat position carefully join the pair and move the levers to the dished or cupped position. If you have been careful to insure that no dirt has spoiled the seal between the cups it will be impossible for the average student to pull them apart. Occasionally, a very strong adult may be successful. If time permits create two teams of three students each to provide the pulling force. Arrange the students so the two strongest hold the handles on opposite sides and the assistants help by pulling on the arms of the leader.
CAUTION! Insure that there is a long clear area behind each team. In the event that some dirt caused a small leak between the cups, air will enter the middle chamber destroying the relative vacuum and allowing the cups to separate suddenly. Also explain to students the risk of this event and brace themselves in such a manner to prevent a fall.
Depending on the age of the group the discussion can continue with a simple calculation of the force necessary to successfully separate the disks. Using pi times the radius squared, for area of a circle, a four inch disk will cover about 12 square inches. Using fifteen (rounding 14.7) the air pressure on the disk will be about 180 lbs. This assumes a perfect vacuum between the disks. Without any instrument to actually verify this assumption it might be wise to assume that the vacuum is less than perfect and therefore the net pressure difference will be somewhat lower.
CONCLUSION and DISCUSSION
Encourage students to tell what they have learned. Look for and reinforce statements that show implications not just isolated facts. Were they surprised? Did they expect that the disks could easily be pulled apart? Calculate how much air pressure could be found on just one desktop! What happens to the human body when it is exposed to very low air pressure such as on a mountain top? Why do mountain climbers carry oxygen tanks? How do we protect astronauts in space where a vacuum exists? How does .smoking affect a person’s ability to cope with high altitudes? What does it mean when the weather map shows areas of high and low pressure?
[Answer: Highs and Lows resulting in certain weather patterns cause relatively small and gradual changes in air pressure. Weather forecasters generally report pressure in inches of mercury as shown on the older style barometers. Converted to pounds per square inch a pressure change from 29 inches of mercury (a low barometric pressure) to 31inches of mercury (a high barometric pressure) would convert to approximately one pound per square inch change. People who report that they can “feel” the pressure change are usually responding to changes in relative humidity or a combination of factors that may accompany an approaching storm.]
Extra credit discussion. Students who find this demonstration interesting may want to do an internet search on topics such as air brakes or pneumatic controls. Both of these commonly used techniques rely on changes in air pressures to cause motion at a distance. Commercial buildings can employ pneumatic controls to regulate huge air handling ducts at a distance from the room needing air flow regulated. Meteorologists monitor air pressure constantly as an indicator of storm movements and to make wind forecasts.
The next lesson. Much has been written about what makes an airplane fly, or more specifically, how does a wing develop lift. Merely stating that air pressure is the answer is a gross oversimplification and denies students a true understanding. Numerous “table-top demonstrations are available and present an eye-popping visual proof how a wing can lower air pressure on its top side resulting in a considerable lifting force. Visit our demonstration table for a hands-on experience illustrating this fascinating topic.
This information has been extracted from the Air Camp curriculum supported by EAA chapter 1158, West Bend, Wisconsin. The material is provided for your use; however, if it is reproduced credit is required. Thank you.
Paul Lupton. Go to: eaa1158.org, for more information about Air Camp