When driving a car or riding a bike, you only have to be concerned with turning left or right, other than obviously moving forward. Airplanes, however, can turn on three axis. Tie a string onto a model airplane. Cut the flaps off of the top of a cardboard box, and lay the box on it's side. Suspend the model airplane inside the box by poking a hole in the box and feeding the string up through the hole and taping it to the box. Use your model to demonstrate the three axis that an airplane can move around, namely pitch, roll and yaw. Pitch is the up and down movement of the front or back of the plane. Roll is where one of the wings dips. Yaw is a turning of the plane left or right on its axis.
Airplane wings are optimally shaped to force the air traveling over them to move faster, and this causes a lowering of pressure on top of the wing. When air moves swiftly across the surface of an object, it lowers the air pressure above it. Place two chairs about 3 feet apart, with the back of the chairs facing each other. Tie a piece of string between the chairs at the top of the chair backs. In the middle of the string, loosely tie a 10-inch length of 1-inch-wide lightweight ribbon. The ribbon will hang vertical due to gravity. Hold the ribbon out horizontally and turn on a hair dryer on its highest cool setting. Aim the air stream across the top of the ribbon. Let go of the ribbon and it will continue to stay horizontal. This is due to the lower air pressure across the top of the ribbon.
In aviation, the resistance of air on an object as it moves forward is called "drag." Friction with the air slows down objects as they move through it. Demonstrate how the shape of an object affects drag on it. Gather three identical sheets of paper. Stand on a step stool and drop one piece of paper. Crumple up another piece into a small ball and drop it from the same height. Make a paper airplane from the third piece of paper and drop it with the front of the plane aiming toward the ground. Gravity pulls all of these paper objects down and gives them speed through the air. Compare the length of time it takes each piece of paper to reach the floor and draw a conclusion regarding air friction on the different shapes of paper.
Airplanes are "heavier than air" vehicles, but giant hot-air balloons that can carry people up into the sky are "lighter than air." They are filled with hot air, and hot air rises. Prove that hot air rises by turning on a toaster and blowing bubbles across the top of it. As the bubbles encounter hot air coming from the toaster, they will rise.