In steady flow (when the velocity vector-field does not change with time), the streamlines, pathlines, and streaklines coincide. This is because when a particle on a streamline reaches a point, , further on that streamline the equations governing the flow will send it in a certain direction . As the equations that govern the flow remain the same when another particle reaches it will also go in the direction . If the flow is not steady then when the next particle reaches position the flow would have changed and the particle will go in a different direction.

A streamtube is a collection of streamlines.

It streamlines the nose.

they can use streamlines only they get less range, around 5ft less. and they arent as accurate. that being said, i got a spectre that hit 40ft stock and shot streamlines at 45ft, so you should check it out. a pack of streamlines is 5$ AUD. or something in USD

The direction of the velocity of a fluid at any point is taken to be tangential to its streamline at that point. When two streamlines intersect two tangents can be drawn at the point of intersection. It inturn means that the fluid has velocity in two different directions which is not possible. Therefore 2 streamlines cannot intersect.