Hodograph

Hodograph in kinematics is a curve of velocities. If a point move along any path its speed at any point has a definite value, and it is then moving in a definite direction, tangentially to the curve at that point. If from any convenient point lines be drawn representing in magnitude and direction the velocities of the actual moving point along its path of motion, the extremities of these lines will be a series of points forming a new curve. This is called the hodograph, and the rate of motion of the hodograph point measures the acceleration, or rate of change of velocity of the moving point. The hodograph of a projectile is a straight- line ; that of any planet, in regard to its motion round the sun, is a circle.