Tarah S. Cherry
MATERIALS NEEDED
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Photocopies of the diagrams interspersed in this activity, paper strips 2 inches wide and 4 inches long, a rubberband-powered model airplane made of balsa-wood, a balloon, baseball, whiffle ball or styrofoam ball the same size as the baseball, a hand-held hair dryer, modeling clay, protractor, graph paper, and a candle.
OBJECTIVE
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Students are introduced to the four basic principles of flight. Students watch or get involved n demonstrations of the four principles, air pressure and the axis of rotation. Exhibits A, B, C, D, E, F, and G.
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1. EXPLAIN: Four basic principles govern flight. Two involve natural forces; two must be created.
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Gravity
—is the natural force that keeps an airplane on the ground or pulls it to Earth when in flight. The Earth pulls any object toward it, and so do the moon, planets and stars. Isaac Newton’s law of gravitational action states that there is a force of attraction between any two massive particles in the Universe.
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Lift
—The force supporting the weight of an airplane. This force of lift must be equal to the weight of the airplane in order for the airplane to maintain level flight. If the lift is more than the weight, the airplane accelerates upward. If the lift is less than the weight, the airplane accelerates downward.
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Drag
—The resistance of air to an object moving through it. The faster an object moves, the more drag it creates. Drag is proportional to the square of the speed. The more streamlined an airplane is designed, the less drag it produces, everything else being equal. The less drag an airplane produces, the faster it can fly.
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Thrust
—The force created by engine power to overcome drag. For an airplane to maintain constant air speed, the thrust and the drag must be equal. If thrust is greater than drag, the airplane speeds up; if thrust is less than drag, the airplane slows down.
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2. EXPLAIN: For an airplane to fly, lift must be equal to or greater than gravity. Because gravity acts on all objects according to the mass of the object, the heavier the plane, the greater the lift needed to overcome gravity. For this reason, airplanes are designed to be as light as possible.