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Sir Isaac Newton first presented his three laws
of motion in the "Principia Mathematica Philosophiae Naturalis"
in 1686. His third law states that for every action (force) in nature
there is an equal and opposite reaction. In other words, if object A
exerts a force on object B, then object B also exerts an equal and
opposite force on object A. Notice that the forces are exerted on
different objects.
For aircraft, the principal of action and reaction is very
important. It helps to explain the generation of lift
from an airfoil. In this problem, the air is deflected downward by
the action of the airfoil, and in reaction the wing is pushed upward.
Similarly, for a spinning ball, the air is
deflected to one side, and the ball reacts by moving in the opposite
direction. A jet engine also produces thrust
through action and reaction. The engine produces hot exhaust gases
which flow out the back of the engine. In reaction, a thrusting force
is produced in the opposite direction.
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