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Measuring Motion - Distance Vs Displacement When thinking about and determining speed or velocity, there are two terms that are very important since speed and velocity are calculations dependent upon them. The two terms are distance symbolized as (d) and displacement which is symbolized by (x). Distance and displacement are two quantities that may seem to be the same yet have distinctly different definitions and meanings There are two types of measurements in physical science: scalar and vector. Scalar measurements are one-dimensional physical quantities that can be described by a single real number and usually includes units. In other words, a scalar measurement is a physical quantity that has only magnitude but no direction, unlike a vector measurement that includes magnitude and direction. . Distance is a scalar quantity that refers to "how far an object has traveled" during its motion. Speed's calculation is dependent upon distance, which means speed is a scalar measurement as well. Displacement is a vector quantity that refers to "how far an object is from its starting position"; it is the object's overall change in position. Velocity's calculation is dependent upon displacement. Since displacement is a vector quantity, so is velocity. To test your understanding of the difference between displacement and distance, consider the motion depicted in the diagram below. A student walks 8 meters East, 4 meters South, 8 meters West, and finally 4 meters North around the perimeter of a school. In this scenario, the student walked a distance of 24 m since 8m + 4m + 8m + 4m. The distance is 24m, but what is the student's displacement? After the student walks the distance of 24 m 8 m around the school, he ends up in the same position he started from so how far is he from his starting position? If you said 0 m, you're right! The student has walked a total distance of 24 meters, but his displacement is 0 meters. He ended in the E wut same place he started from. During the course of his motion, he has covered 24 meters of ground (distance = 24 m). Yet when he is finished walking, he is in the same place he started - i.e., there is no displacement for his motion (displacement = 0 m). Displacement, being a vector quantity, relies on direction. 8 m The 8 meters east cancels the 8 meters west; and the 4 meters south cancels the 4 meters north. Remember, vector quantities such as displacement are direction aware. Scalar quantities such as distance are dependent on direction. In determining the overall distance traveled by the student, the various directions of motion can be ignored. Let's draw a vector diagram to scale to show this. Vector diagrams are drawn "head to tail". The starting point is the "tail" of the first vector and the "head" should point in the direction he is traveling. Directions: Draw each vector this way to complete the vector diagram on the grid below. Start at the dot. What scale did you use for your vector diagram? Write a number sentence to show the distance (d). Write a number sentence to show the displacemen (x)
