Vectors and vector addition

Some physical quantities, such as time, temperature, mass, density, and electric charge, can be described completely by a single number with a unit. Many other quantities, howevere, have a directional quanlity and cannot be described by a single number. A familiar example is velocity. To describe the motion of an airplane, we must say not only how fast it is moving, but also in what direction.


When a physical quantity is described by a single number, we call it a scalar quantity.In contrast, a vector quantity has both magnitude and a direction in space.

The simplest vector quantity is a displacement.Displacement is simply a change in position of point. such as the change of position from point p1 to point p2 by a line from P1 to p2 with an arrowhead at p2 to represent the direction of motion. Displacement is a vector quantity because we must state not only how far the particle moves, but also in what direction.



Fig.1.Vector A is the displacement from point P1 to point P2



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