CHAPTER LXII1 



MECHANICS OF MATERIALS 



Definitions. Mechanics is that science which treats of 

 the action of forces upon bodies and the effects which they 

 produce. 



Statics is that division of the science of mechanics which 

 treats of the forces acting on a body at rest, or in equilibrium. 

 In architectural design, statics is the principal branch of 

 mechanics to be considered, as nearly all the forces involved 

 are those of rest. 



Action of a Force. A force acting upon a body tends to 

 produce motion in two ways: 



1. It tends to produce motion in the direction of the 

 force. 



2. If a point of the body be fixed, it tends to produce 

 motion about that point. 



Condition of Equilibrium. Since a force acting upon a 

 body tends to produce motion in two ways, the following 

 conditions must be filled in order that equilibrium exist : 



1. The resultant of all the forces tending to move the 

 body in any direction must be zero. 



2. The resultant of all the forces tending to turn the body 

 about any point must be zero. 



The moment of a force about a point is the product of the 

 force into the perpendicular distance from the line of the 

 force to the point. 



Moments tending to produce clockwise rotation are called 

 positive moments, and those tending to produce counter- 

 clockwise motion, negative moments. 



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