hodograph

/HH OW1 D OW0 G R AE0 F/
noun
  1. 1

    A curve described by the moving extremity of a line whose other end is fixed, this line being constantly parallel to the direction of motion of, and having its length constantly proportional to the velocity of, a point moving in any path; used in investigations respecting central forces.

Source: https://en.wiktionary.org/wiki/hodograph