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Free Fall and Graphs of Motion A Falling Apple Consider an apple falling from a tree It starts from a position of rest and gains speed as it falls. Gravity causes the apple to accelerate as it falls. Free Fall Describes objects that are only affected by gravity. The speed of an object in free fall increases or decreases by 9.81 m/s each second. 9.81 m/s2 is the acceleration due to gravity. “g” represents the acc. due to gravity Straight Up Now consider an object tossed straight up. As an object moves upward, it is accelerating (speed ). - the object slows at a rate of 9.81 m/s2 (acc due to gravity). The highest point At its highest point, the object has an inst. speed of zero (b/c it has to stop to change directions) The object will fall as if it were dropped from its highest point. The way down As the object is falling, it will accelerate at 9.81m/s2 The falling object will its speed by 9.81m/s each second. Height and Velocity The inst. speed at points of equal elevations are the same. The velocities are different b/c they are in opposite directions. Air Resistance & Free Fall Causes objects of different shapes to accelerate differently (stone vs feather) With negligible air resistance, falling objects can be considered freely falling. The path is symmetrical. Acceleration is constant. The magnitude of the velocities is the same at equal heights. Group Discussion Two stones are thrown from a cliff at the same time with the same speed, one upward and one downward. Which stone, if either, hits the ground first? Which, if either, hits with the higher speed? In a group discussion, make your best argument for each possible prediction. Set up numerical examples and solve them to test your prediction.
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