What is Kinematics?

Kinematics is the geometry of pure motion - motion considered abstractly, without reference to force or mass. Engineers use kinematics in machine design. Although hidden in much of modern technology, kinematic mechanisms are important components of many technologies such as robots, automobiles, aircraft, satellites, and consumer electronics, as well as biomechanical prostheses. In physics, kinematics is part of the teaching of basic ideas of dynamics; in mathematics, it is a fundamental part of geometric thinking and concepts of motion. The development of high-speed computers and robotics, and the growth of design synthesis theory and mechatronics have recently revived interest in kinematics and early work in machine design.

In his 1834 Essai sur la philosophie des sciences, André-Marie Ampère (1775-1836) sketched the outlines of a new field of study he named "cinematique," from the Greek kinema, motion:

There exist considerations which if sufficiently developed would constitute a complete science, but which had hitherto been neglected, or have formed only the subject of memoirs or special essays. This science ought to include all that can be said with respect to motion in its different kinds, independently of the forces by which it is produced. ... It should treat in the first place of spaces passed over, and of times employed in different motions, and of determination of velocities according to the different relations which may exist between those spaces and times (In Richard S. Hartenberg and Jacques Denavit, Kinematic Synthesis of Linkages [New York: McGraw Hill, 1964] 14-15; translation by Hartenberg and Denavit).

Working in the decades following Ampère's death, Franz Reuleaux (1829-1905) is considered the founder of modern kinematics. Reuleaux called it "the study of the motion of bodies of every kind…and the study of the geometric representation of motion" (Kinematics of Machinery 56).

Kinematics flourished in the 19th century as machine inventors learned to transmit information and forces (power) from one element in the machine to another. Steam- and water-based machines revolutionized the l9th century, but both of those energy sources generate circular motions, creating the need to convert these steady circular motions into nonsteady linear and curvilinear motion for machine applications. Practical inventors as well as mathematicians [Artobolevskii 1964] took up the challenge to create input-output kinematic devices that could convert circular motion into noncircular, complex, three-dimensional, intermittent motions. Thousands of mechanisms were invented, designed, and built, nurturing the widespread use and manufacture of machines. Reuleaux set out to codify, analyze, and synthesize kinematic mechanisms so that engineers could approach machine design in a rational way. He laid the foundation for a systematic study of machines by defining clearly the machine and mechanism, determining the basic mechanical building blocks, and developing a system for classifying known mechanism types. Reuleaux was the author of Theoretische Kinematik: Grundzüge einer Theorie des Machinenwesens, which appeared in English in 1876 as The Kinematics of Machinery: Outlines of a Theory of Machines. He also published another important work related to design of machines in 1861, which was translated as The Constructor (1893). Mechanical models designed by Reuleaux to embody his classification of kinematic mechanisms are the basis for the Kinematic Models for Design Digital Library (KMODDL).