Chapter 1 - Forces and moments

Abstract

This chapter presents a brief examination of the basic principles of force and moments, because the solution of many of the problems concerned with ship stability involves an understanding of the resolution of forces and moments. A force can be defined as any push or pull exerted on a body. When two or more forces are acting at a point, their combined effect can be represented by one force that has the same effect as the component forces. Such a force is referred to as the resultant force, and the process of finding it is called the resolution of the component forces. The chapter explains resolution of forces with respect to three cases: when two forces act in the same straight line, when two forces do not act in the same straight line, and when two forces act in parallel direction. The moment of a force is a measure of the turning effect of the force about a point. The turning effect depends upon the magnitude of the force and the length of the lever upon which the force acts—the lever being the perpendicular distance between the line of action of the force and the point about which the moment is being taken. When two or more forces are acting about a point, their combined effect can be represented by one imaginary moment called the resultant moment. The process of finding the resultant moment is referred to as the resolution of the component moments.