LAWS OF BONE ARCHITECTURE 187 



that are universally accepted by mathematicians, engineers and 

 scientists will be given. 



A clear understanding of the definitions and mechanical prin- 

 ciples given in the following paragraphs, 1 to 63 inclusive, is 

 indispensable in solving problems involving forces and stresses. 

 Obviously, in a paper of this nature a discussion of mechanical 

 principles must be brief and confined to the essentials. The 

 interested reader can find a full discussion of the subject in any 

 of the standard text-books of mechanics. 



Definitions 



1. Mechanics is that branch of dynamics that deals with the 

 laws that govern the action of forces upon solid bodies. 



2. Statics is that branch of mechanics that deals with the 

 laws and conditions of forces acting upon solid bodies at rest, 

 as for example, bridges, buildings, arches and other structures. 



3. Graphic statics deals with the graphic representation of 

 forces acting upon solid bodies at rest. 



4. Force is that action of one body upon another which tends 

 to change, or changes, the state of rest (or motion) of the body 

 acted upon. Force has direction, magnitude, and a point or 

 place of application, and is defined when these are known. The 

 line of action of a force is the line drawn through the point of 

 application of the force, or through the point at which the force 

 may be regarded as concentrated, parallel to the direction of the 

 force. The usual unit in use as a measure of force is the pound 

 (or ton, kilogram, etc.), which is the force exerted by gravity 

 upon the standard weight also called a pound (or ton, kilo- 

 gram, etc.). 



5. Effect of force. A force is the cause that may produce the 

 following effects: a) an opposition or balancing of other known 

 forces; b) change of motion of the body either in direction or 

 velocity; c) a measurable distortion of the solid body itself. 

 The second effect relates to the study of the laws of motion and 

 need not be further considered; the first and third apply to the 

 subject of statics. 



