Flow due to a moving sphere at small Reynolds numbers

1 Flow due to a moving sphere at small Reynolds numbers 

At low Reynolds numbers the Navier-Stokes equation for a stationary flow, dv/d t  

This equation and the continuity equation for an incompressible liquid, eq 1.6, determine completely the flow of the liquid. 

The vector field v(r, t) is free of sources meaning that it can be discussed with the help of its accompanying rotational field, defined by a vector A(r,t) related to v(r,0 

Here A is an axial vector (or pseudovector) whereas v is a polar vector. Axial vectors show the particularity of being changed to their opposites upon inversion of the coordinate system, in contrast to polar vectors (this is the case of the magnetic field in Electromagnetism). 

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