MECHANICS. 



DR. WALLIS defines mechanics to be the geo- 

 metry of motion. 



Subdivisions of Mechanics. 



Mechanics, in its most extensive meaning, is the 

 science which treats of quantity, of extension, and of 

 motion. That branch which considers the state of 

 solids at rest, such as their equilibrium, their weight 

 and their pressure, &c. is called Statics ; and that 

 which treats of their motions, Dynamics. When 

 fluids are considered instead of solids, that branch 

 which treats of their equilibrium, &c. is called Hy- 

 drostatics; and that which treats of their motion, Hy- 

 drodynamics. 



By Sir Isaac Newton this science is divided into 

 practical and rational mechanics ; the first relating to 

 the mechanical powers; (viz. the lever, balance, 

 wheel and axis, pulley, wedge, screw, and inclined 

 plane;) the latter (or rational mechanics) to the 

 theory of motion; showing, when the forces or 

 powers are given, how to determine the motion that 

 results from them ; or conversely, when the circum- 

 stances of the motion are given, how to trace the 

 forces or powers from which they arise. 



Quantities. 



The five mechanic quantities are 



1 . The quantity of matter moved. 



2. The constant force that moves it. 



3. The space described from rest. 



4. The time of description. 



5. The velocity acquired. 



