The vector product, or cross product, is a form of multiplication of two vectors which yields a vector. The vector product of the two vectors a and b, written

a/b is defined as the vector

ab ½a½ ½b½ sin u nˆ,

where u is the angle between a and b when their initial points are brought

into coincidence, and nˆ is a unit vector perpendicular to both a and b point-

ing in the direction in which a right-handed screw would advance if rotated

from a to b. The situation is illustrated in Fig. 135.