Answer:
When analyzing forces in a structure or machine, it is conventional to classify forces as external forces;
constraint forces or internal forces.
External forces arise from interaction between the system of interest and its surroundings.
Examples of external forces include gravitational forces; lift or drag forces arising from wind loading;
electrostatic and electromagnetic forces; and buoyancy forces; among others. Force laws governing these
effects are listed later in this section.
Constraint forces are exerted by one part of a structure on another, through joints, connections or contacts
between components. Constraint forces are very complex, and will be discussed in detail in Section 8.
Internal forces are forces that act inside a solid part of a structure or component. For example, a stretched
rope has a tension force acting inside it, holding the rope together. Most solid objects contain very
complex distributions of internal force. These internal forces ultimately lead to structural failure, and also
cause the structure to deform. The purpose of calculating forces in a structure or component is usually to
deduce the internal forces, so as to be able to design stiff, lightweight and strong components. We will
not, unfortunately, be able to develop a full theory of internal forces in this course – a proper discussion
requires understanding of partial differential equations, as well as vector and tensor calculus. However, a
brief discussion of internal forces in slender members will be provided in Section 9.
Explanation:
