Scalars and Vectors

Some of the physical quantities mentioned are specified simply by a number and a unit. For example, a mass may be stated as 4 kg, a temperature as 15 °C, and a time interval as 25 min. These quantities are called scalars; they have magnitude but no direction. Other physical quantities, called vectors, are specified by both a magnitude and a direction. For example, a wind velocity might be given as 20 km/h from the southeast. Almost all the quantities we will encounter in this book are classified as either scalar or vector. An important property of vectors is that they do not combine according to the rules of ordinary algebra, in the next chapter we will use the vector quantity displacement, which is defined as a change in position, to present the rules of vector addition and vector products.

A vector quantity is usually printed in boldface, A, and is typed or written with an arrow on top, . The magnitude of a vector is a positive scalar and is written as either |A| or A. We will come across many vector quantities, such as force, torque, momentum, and electric field strength.*

CHAPTER 2

Kinematics

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