Strength of Materials

1.3 EXTERNAL AND INTERNAL FORCES

1.3.1 External Forces

Force may be considered as a measure of interaction between two systems. The interaction may be of mechanical, electrical, electromagnetic or chemical in origin. In this book, the interaction by mechanical origin alone is discussed. Mechanical interaction may be through contact with other members or due to the effects of fluid pressure, gravity or inertia.

A system (body) in a specified origin surrounded by other systems is considered. The body can be isolated from the actions of all the outside systems by representing such actions as a set of forces. These forces are denoted as external forces. Figure 1.1 represents such an isolated body and are the external forces acting on the system. ...