Fundamental Laws and Basic Concepts

Abstract

Before taking up the main subject of this chapter let us make some comments about three types of time derivatives that we shall use in this book. The first is the partial derivative ∂/∂t ; when applied to some function ${\rm{f}}({\rm{t}},{\rm{\vec x)}}$, it expresses the rate of variation of the quantity f at a given and fixed point determined by the vector ${\rm{\vec x}}$ whose components x_i (i = 1,2,3) are x, y, z in rectangular coordinates.