Explain how to identify a starting position on a line.

Displacement is defined as the distance, in any direction, of an object relative to the position of another object. Physicists use the concept of a position vector as a graphical tool to visualize displacements. A position vector expresses the positionof an object from the origin of a coordinate system

A position vector expresses the position of an object from the origin of a coordinate system.

Position vector is basically a straight line which has one of its ends end fixed to a body and whereas, the other end is attached to a moving point which tells the position of that specific point relative to the body. As the point accelerates, the position vector will vary its length and the direction accordingly.