Kinematics

Kinematics is the study of motion. It does not investigate the cause which produces motion, but simply the space-relations from time to time, of the moving body. The more important motions are (1) uniform motion in a straight line when the speed is the same at every point, and the distance travelled is directly proportional to the time; (2) uniformly accelerated motion when the body starts from rest and increases its speed uniformly, the distance travelled from rest being in this case proportional to the square of the time and to the rate of change, of speed; (3) uniform motion in a circle; (4) simple harmonic (q.v.) motion, which is an oscillatory motion about a point, with a varying acceleration that is always proportional to the distance of the moving body from the centre. The propagation of a state of motion through a medium without actual transit of the particles composing the medium, is said to be produced by waves. The constituent particles oscillate about fixed positions, and transmit that condition of oscillation in all directions, with a speed that depends upon the elasticity and density of the medium.