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Distance & Displacement. Distance & Displacement. Distance and displacement are two quantities which may seem to mean the same thing, yet have distinctly different definitions and meanings
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Distance & Displacement • Distance and displacement are two quantities which may seem to mean the same thing, yet have distinctly different definitions and meanings • Distance is a scalar quantity which refers to "how much ground an object has covered" during its motion.
Distance & Displacement • Displacement is a vector quantity which refers to "how far out of place an object is"; it is the object's change in position. • Recall that a scalar has only a magnitude and a vector is described by both a magnitude and a direction
Distance & Displacement • To test your understanding of this distinction, consider the following motion depicted in the diagram below. A physics teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North.
Distance & Displacement • Even though the physics teacher has walked a total distance of 12 meters, her displacement is 0 meters. During the course of her motion, she has "covered 12 meters of ground" (distance = 12 m).
Distance & Displacement • Yet, when she is finished walking, she is not "out of place" - i.e., there is no displacement for her motion (displacement = 0 m). Displacement, being a vector quantity, must give attention and regard to direction. The 4 meters east is canceled by the 4 meters west; and the 2 meters south is canceled by the 2 meters north.
Distance & Displacement • Picture the movement of the teacher on a piece of graph paper. • If the teacher moves up or to the right, her movement is positive • If the teacher moves down or to the left, her movement is negative
Distance & Displacement • Now for a final example. Seymour Butz views football games from under the bleachers. He frequently paces back and forth to get the best views. The diagram below shows several of Seymour's positions at various times. At each marked position, Seymour makes a "U-turn" and moves in the opposite direction.
Distance & Displacement • In other words, Seymour moves from position A to B to C to D. What is Seymour's resulting displacement and distance of travel?
Distance & Displacement • Seymour’s distance is 95 yards • He traveled 35 yards from point A to point B. • He then traveled 20 yards from point B to point C. • Finally he traveled 40 yards from point C to point D.
Distance & Displacement • Seymour has a displacement of –55 yards • He travels –35 yards left from point A to point B. • He then travels +20 yards to the right from point B to point C. • Finally he travels –40 yards to the left from point C to point D.