Springs undergo deformations that cannot be neglected when acted upon by forces or moments. All bodies to be studied in this book are rigid, except for springs. Most bodies encountered in engineering work can be considered rigid from the mechanical analysis point of view becase the deformations that take place within these bodies under the action of loads can be neglected when compared to other effects produced by the loads. A body is said to be rigid when the relative positions of its particles are alwaysВ fixed and do not change when the body is acted upon by any load (whetherВ aВ force or a couple). The size of a body affects the results of any mechanical analysis on it. A body is formed by a group of particles. The size of a particle is very small compared to the size of the system being analysed. A particle is a body whoseВ size does not have any effect on the results of mechanical analyses on it and, therefore,В its dimensions can be neglected. The ability to understand mechanics and many other engineering disiciplines is dependent on mastering the concept of equilibrium. The concept must be really understood by every student. The conceptВ of equilibrium is the most basic and most important concept in engineering analysis. In statics, the concept of equilibrium is usually used in the analysis of a body which is stationary, or is said to beВ in theВ state of static equilibrium.

There is no unbalanced force or unbalanced couple acting on it. A body under such a state is acted upon by balanced forces and balanced couples only. The concept of equilibrium is introduced to describe a body which is stationary or which is moving with a constant velocity. 3.3 EQUILIBRIUM EQUATIONS FOR A RIGID BODY

Static equilibrium 3d problems