Raymond W. Brooks
The atmosphere is the mixture of gases that surround the earth and are held here by the force of gravity. There are several layers of the atmosphere which are separated by differences in temperature. As airplanes fly only in the troposphere and stratosphere we will concern ourselves with these two layers only.
The troposphere is the layer of the atmosphere that we live in. Most of the air is nitrogen (78%) and oxygen. (21%) This dilution of nitrogen is very important as oxidation would take place much more rapidly probably causing more damage by fires and rusting than we now experience.
Oxygen is very flammable and a good way to show this property is to do an electrolysis of water experiment. Use an inverted test tube to collect the gases hydrogen and oxygen then test each with a glowing splint placed at the mouth of the test tube to observe the reaction. The oxygen in the air is necessary for the combustion of the fuel in airplane engines to operate in the atmosphere.
Air like water is a fluid and has similar characteristics. One is that it exerts pressure in all directions and pressure increases with depth. A good way to show this is to place a piece of rubber over a thistle tube and connect it to a u-shaped piece of glass containing colored water with rubber tubing. Submerge the tube in water and have the students observe what happens to the water level in the u-shaped tube. After completing this exercise ask the students what they think will happen when you rotate the thistle tube in the water but keep the mouth at the same depth. This exercise will help the student to remember that air pressure decreases as you ascend and that it is exerted equally in all directions. You might also ask them what happens to them when they try to reach the bottom of a swimming pool. This will also lead to a discussion of flight suits, diving suits, and pressurized cabins.
Some jet planes fly in the lower layer of the stratosphere and so this can lead to a discussion about solar flares and other sources of radiation plus the ozone layer which protects us from harmful ultraviolet radiation from the sun.
