An object that falls through a vacuum is subjected to only one external force, the gravitational force, expressed as theweight of the object. An object that is moving only because of the action of gravity is said to be free falling and its motion is described by Newton's second law of motion. With algebra we can solve for the acceleration of a free falling object. The acceleration is constant and equal to the gravitational acceleration g which is 9.8 meters per square second at sea level on the Earth. The weight, size, and shape of the object are not a factor in describing a free fall. In a vacuum, a beach ball falls with the same acceleration as an airliner. Knowing the acceleration, we can determine the velocity and location of any free falling object at any time using the following equations.
X = .5 * a * t^2
where a is the acceleration, V is the velocity, and X is the displacement from an initial location. If the object falls through the atmosphere, there is an additional drag force acting on the object and the physics involved with describing the motion of the object is more complex.
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