I understand that an example of a physical interpretation of the line integral of a scalar function with respect to arc length [tex]\int_C f(x,y,z)ds[/tex] might be the total mass of a wire where f describes the linear density of the wire. But can anybody give an example of a physical or geometric interpretation of the line integral with respect to x (or y, or z)? i.e. given some specific function f(x,y,z) and points A and B on that curve I can calculate [tex]\int_C f(x,y,z)dx[/tex] from A to B to answer an exercise in the textbook. But what would it mean?