Basic Kinetics

Abstract

The motion of mechanical systems is caused and influenced by forces and torques. Kinetics describes the effect of forces and torques on free systems. Constrained systems are thus assigned to free systems in accordance with the method of sections. Starting from the kinetics of the point, we will proceed to the kinetics of the rigid body and of a continuum. The basic equations of kinetics, the Newton and Euler equations, constitute, together with the law of conservation of mass, the mechanical balance equations. We also call Newton’s equations the principle of conservation of linear momentum or the momentum balance and Euler’s equations the principle of conservation of angular momentum, the balance of moment of momentum, or angular momentum balance. Momentum balance and the angular momentum balance are independent basic equations for a continuum, while for free point systems both equations are mutually convertible. The momentum balance and angular momentum balance can also be supplemented by the energy balance, which is however dependent on the first two principals in the case of isothermal processes in a continuum. Nevertheless, simpler solutions are at hand in many cases by using the energy balance.