Learning objectives By the end of this chapter, you should be able to:
distinguish between vector and scalar quantities combine and resolve vector quantities. Physical quantities can be divided into two basic types:
• scalar quantities have magnitude only, with no direction in space • vector quantities have magnitude and direction. Scalar examples distance (m)
Vector examples displacement (m)
speed (m s–1)
velocity (m s–1) force (N)
For the Leaving Certificate Physics course, you must know whether a quantity is vector or scalar. You can do this by learning off the following list of vector quantities, as all other quantities in this book are scalar.
Vector quantities
acceleration displacement
magnetic lux density momentum
electric ield strength velocity force
Representing vectors Vector quantities can be represented with arrows.
• The length of the arrow is proportional to the vector’s magnitude, so, for example, the arrow for a 10 N vector is twice as long as a 5 N vector arrow.
• The direction of the arrow corresponds to the vector’s direction.
Examples of vectors are given in Fig. 3.1. N 12 N W a S 45° E W b S
FIG. 3.1a 12 newton force acting 45˚NE; b 8 newton force acting east
LEAVING CERTIFICATE PHYSICS 23 8 N E N
A scalar quantity has magnitude only and has no direction in space.
A vector quantity has both magnitude and direction.
NOTE
We will explain many of these vector quantities in later chapters.
STS
Simple vector arrows are used to show forces acting on bodies such as air moving over and around a car in a wind tunnel.
