Francis J. Degnan
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I. Introduction
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II. Gravity and Pressure
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Student activity sheet, Guess What?
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Teacher outline
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III. Gases
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Student activity sheet, Now What?
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Teacher outline
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IV. Fluids
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V. Flight
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Student activity sheet, What Now?
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Teacher outline
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VI. Constructions
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Teacher outline
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Student activity sheets
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The Twister
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The Circle Flier
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Student data sheet
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VII. Student Bibliography
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VIII. Teacher Bibliography
I. Introduction
The title implies taking off, reaching for the limitless skies. The students will be challenged to observe, predict, test and generalize through a series of demonstrations and investigations. These exercises will introduce and clarify some aspects of the science of aerodynamics. Gravity, pressure and the properties of gases are areas of initial interest. The investigations in these areas include hands on activities that will hopefully motivate the students to readily gather their data, record their findings and support their ideas.
This unit is primarily designed for presentation to the elementary student in grades three, four and five. It is intended to introduce the key elements of scientific investigation; observation, data collection and prediction. A majority of the activities ask the students to predict an outcome for an individual event. Some of these experiments are straightforward but others have been chosen because they to not result in what might be expected. They are intended to intrigue students and cause them to question and formulate conclusions.
The activities emphasize a sequential development toward an appreciation of some of the aspects of what makes an airplane fly. Considerations are first given to gravity, pressure and gases. The student should gain a clearer understanding that these are the elements in his environment that have a great effect upon him, even though in daily life they are usually taken for granted. It should become evident that the forces of pressure and gravity must be considered in order for flight to take place in our atmosphere. The activities that follow these elaborate upon Bernoulli’s Law, a principle directly related to flight. Finally there are constructions for the student to build. This involves the making of three different types of flying paper objects and the collection of data on their accuracy, duration and length of flight. Many of the activities can be done by the students individually or in small groups. This unit allows the teacher to have a rich resource of activities for the class to do. Most of the lessons are designed to be presented in a fifty minute period, however the constructions and the presentations of the Bernoulli activities may demand an extended period.
After some sections there are student activity sheets that are accompanied by teacher planning outlines. The student sheets in the unit have been reduced, they may be returned to original size by setting the enlarger on a copier to 120%. There is also material on file at the Yale-New Haven Teachers Institute office on this topic if further activities are desired.
II. Gravity and Pressure
Student activity sheet 1
Guess
What?
is to accompany this discussion. Gravity is a component of the environment that is often overlooked. The fact that objects fall and that this fall is due to gravity is usually the extent of the elementary experience. It is with this information that the activities begin to build. The first activity directs that two spheres, in this case balls of different sizes, be dropped simultaneously. The question to be answered is, “Which will land first?” The answer is that they will both hit at the same time. The students can be told that it seemed a radical discovery four hundred years ago when a scientist named Galileo taught that all objects fall with the same speed regardless of size. This was true unless there was air resistance—a topic that is on the next section’s activity sheet for students. Students may have heard Isaac Newton’s name and recall the fall of the apple, but are they aware that the observation of the apple lead him to theorize that the force that pulled the apple toward the earth was the same force responsible for holding the earth together? This force also holds us on our planet and gives us our weight. Our weight is determined by the earth’s gravitational pull on our mass. The gravitational force of this pull in turn is due to the earth’s mass. On other planets that have different masses, different amounts of gravitational force are exerted. Our weight would vary with these changes from planet to planet. Mass is the amount of matter something is made up of, and matter is anything that takes up space. As an extension the class could be asked, “Does an object have weight at the center of the earth?” No, because the earth’s matter pulls on it with the same force in all directions.
Now that we have established some understanding of gravity we can proceed to a consideration of pressure. The second activity is designed to illustrate that in a column of liquid the highest pressure is near the bottom. If three holes are put into a tall can and the can is filled with water the stream of water from the lowest hole will stream out the farthest, the hole half way up less and the top hole the least. Now it’s gravity that is exerting its force on the column of water and it’s the combined weight of the column that creates the pressure that forces the bottom stream out with the most force. Now an analogy must be drawn, this column of water could represent the ocean or our atmosphere! We are at the bottom of an ocean of air! We have columns of air exerting a force on us all the time. Our muscles allow us movement in our world. Astronauts were studied to see if their muscles weakened while in weightless space. Scientists discovered that indeed they did and exercise is necessary in a weightless environment.
This activity on the student’s sheet asks for first a guess of what will happen, what will the shape and distance of the streams of water from each hole be? Tape may be placed over all the holes and one at a time uncovered. Measurements might also be taken to show at what point each of the lower holes stream’s length is equal to the initial length of the stream from the top hole. The seconds hole’s stream will be the same as the top hole’s original stream when there is an amount of water above it equal to the original amount of water above the top hole. When the amount of water above the hole is the same the pressure producing the streams of water are the same.
Activity C checks the understanding of activity B. “If we are at the bottom of an ocean of air, what is above us? . . . above the sheet of newspaper?” When these questions are asked the students should respond that there is a column of air above us and above the paper. If this is a fourth or fifth grade they might multiply the length and width of the newspaper sheet by 14.7 pounds per square inch, the atmospheric pressure at sea level, and arrive at roughly 9,000 pounds rests uppon each average page. Even with these calculations completed the students most likely will not be able to predict that the paper does not move and that the meter stick may very well be broken at the table’s edge after being struck. This exercise provides a vivid examole of the pressure that is exerted at the bottom of our ocean of air.
If practiced in advance the card will stay on when the glass of water is inverted and the water will remain in the glass. This is activity D. This is another deceptive demonstration. We should ask, “Why does the water remain in the glass?” It may remain with the card holding it for only half a minute until the water’s seal is broken, but it is being held for that short time. Again the key to understanding the problem is understanding something else about pressure. In a fluid or gas at rest pressure is transmitted within a gas or fluid equally in all directions at any one point. In this case the direction happens to be up! If we pause a moment and consider the last statement we can understand why water drops are spherical. If an eye dropper is used to drop drops the shape of the drop at first resembles a tear. Once it begins to fall it becomes spherical. The pressure is being exerted equally in all directions creating the spherical shape. The same is true of bubbles rising in the water—they too become spheres as they head towards the surface. The original study of the distribution of pressure in fluids was done by Blaise Pascal in the seventeen hundreds. His work has had far reaching consequences. The principle of pressure distribution that is now called Pascal’s Law is the key in the study of hydraulics.
Guess What?
(figure available in print form)
