sentences:  It is also called velocity field; when evaluated along a line, it is called a velocity profile (as in, e.g., law of the wall).The flow velocity u of a fluid is a vector field
  
  which gives the velocity of an "element of fluid" at a position formula_2 and time formula_3
  
  The flow speed "q" is the length of the flow velocity vector
  
  and is a scalar field.The flow velocity of a fluid effectively describes everything about the motion of a fluid.