Kinematics Case Study (Physics)

Kinematics

Kinematics is the branch of classical mechanics which describes the motion of points (alternatively "particles"), bodies (objects), and systems of bodies without consideration of the masses of those objects nor the forces that may have caused the motion. 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.

Working in the decades following Ampere’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 non-steady linear and curvilinear motion for machine applications.

In real life, we can apply kinematics is that the importance of peak bar velocity and starting posture adopted by a novice weightlifter to the outcome of a Snatch lift. Multiple observations of both successful and unsuccessful attempts were captured using 3D motion analysis (VICON MX: 500 Hz). The following data analysis was then used to derive feedback. In total, 133 attempts of loads ranging from 75 to 100% of 1 repetition maximum (1RM) were performed by the subject (age = 25 years, stature = 171 cm, mass = 74.8 kg, Snatch 1RM = 80 kg).

Variables included peak bar velocity, pelvis, hip, knee and ankle joint angles at the starting position for the right side and the difference between (left minus right) sides. No main effects for load, success, or their interactions were found for peak bar velocity. Starting position kinematics were mostly non-significant between the outcomes of Snatch attempts. Right ankle joint angle was the only exception, where unsuccessful attempts displayed greater (p = 0.0228) dorsiflexion. A more comprehensive finding was achieved through the partition modeling; this analysis provided valuable insight and coaching feedback for the subject in relation to his lower body kinematics at the starting position. Furthermore, the accuracy of this feedback was verified using a holdback data set. Specifically, anterior pelvic tilt (>17.6°) and hip joint (<89.6°) angle were identified as the key features to increasing the likelihood of success. In conclusion, this case study outlines a method of data collection and analysis to assist coaching feedback for an individual.