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The Physics of Motion. The motion of objects can be described in words-words such as distance, displacement, speed, velocity and acceleration. These mathematical quantities that describe motion can be divided into 2 categories: vector and scalar
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The motion of objects can be described in words-words such as distance, displacement, speed, velocity and acceleration. • These mathematical quantities that describe motion can be divided into 2 categories: vector and scalar • Vectors: quantities that are described by both a magnitude and a direction. Ex. Go 200km West • Scalar: quantities that are described by magnitude alone. Ex. Go 200km
Test your understanding… • Consider the following quantities. Write them in your notes and decide whether each is a vector or a scalar. • 5m • 30m/s East • 5min. North • 20 °C • 256 bytes • 4000 Calories
Distance and Displacement • Distance and displacement are two quantities which may seem to mean the same thing, yet they have distinctly different meanings and definitions. • Distance is a scalar quantity which refers to "how much ground an object has covered" during its motion. If an object moves the distance is always positive and increasing. (The odometer in a car measures its distance traveled). • Displacement is a vector quantity which refers to "how far out of place an object is"; it is the object's change in position. Displacement is always compared to the original starting position, and it can be positive, negative or zero.
Example 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. start 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.
Displacement Displacement can be positive or negative, because it includes direction. If a compass direction is given it can be compared to a grid: N (positive) W (negative) E (positive) S (negative)
