Distance


 * __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 quanity which refers to "how much ground an object has covered" during its motion.**
 * __Displacement__ is a vector quanity which refers to "how far out of place an object is"; it's the objects overall change in position.**



To test your understanding of this distinction, consider the motion depicted in the diagram below. A physics teacher walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North. 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). 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 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. Vector quantities such as displacement are //direction aware//. Scalar quantities such as distance are ignorant of direction. In determining the overall distance traveled by the physics teachers, the various directions of motion can be ignored.

Now consider another example. The diagram below shows the position of a cross-country skier at various times. At each of the indicated times, the skier turns around and reverses the direction of travel. In other words, the skier moves from A to B to C to D. What is the coach's resulting displacement and distance of travel? The coach covers a distance of (35 yds + 20 yds + 40 yds) = **95 yards** and has a displacement of **55 yards, left. http://en.wikipedia.org/wiki/Distance

-PRECIOUS L.**