Biomedical Engineering Reference
In-Depth Information
Chapter 3
Center of Gravity
The weight of a body is an ever present force, and its consideration is of basic
importance to any analysis of strength and of structural equilibrium. This chapter
deals with the displacement and the rotation that this force can produce. To consider
the effects it causes, we represent this force acting on a given point of the body,
called the center of gravity of the body.
3.1 Objectives
To discuss the concept of center of gravity of a body
To determine the center of gravity of a body
To discuss the stability of the human body
To classify the state of equilibrium of a body as stable, unstable, or neutral
3.2 Weight and Center of Gravity
An extensive body can be imagined as composed of a very large number of very
small pieces, as tiny as a cell, if this body is, for example, a piece of the human
body. The resultant weight of this body will correspond to the sum of the gravita-
tional forces that act on each of these small pieces. There is a point where we can
consider that the resultant weight is applied, called the center of gravity, C.G. This
fact can be interpreted as if all mass of the body is concentrated at this single point
and, hence, this is the point of the application of the weight force. For homogeneous
bodies of regular shape, the C.G. is in its geometric center. An object will be in
equilibrium when suspended or supported by a force whose line of action passes
through this point, the C.G. But one can ask: why it is so important to know the
body's position of the center of gravity?
To respond to this question, let us begin by analyzing the situations illustrated
in Fig.
3.1
. Various bodies in this figure are in situations that we can ask what
