6 BULLETIN" 556, TJ. S. DEPARTMENT OF AG1ICULTTJBE. 



MISUSE OF TEEMS. 



Considerable confusion often arises from the use of general terms 

 in a limited sense, or with different meanings by different persons. 

 For instance, strength, in the broad sense of the word, is the summa- 

 tion of the mechanical properties or the ability of a material to resist 

 stresses or deformations of various sorts. While such properties as 

 hardness, stiffness, and toughness are not always thought of in con- 

 nection with the term "strength," they are unconsciously included 

 when, in a specific instance, they are important. This may be 

 illustrated by some comparisons of oak and longleaf pine. For 

 floor beams or posts, the pine, because of its strength and stiffness as 

 a beam, has a slight advantage over the oak and is considered 

 "stronger." For handles, vehicle or implement parts, oak, because 

 of its greater toughness, or shock-resisting ability, is decidedly 

 superior to the pine and is considered "stronger." Thus it is seen 

 that the term "strength" may refer to any one of many properties 

 or combinations of properties, and is necessarily indefinite in meaning 

 unless so modified as to indicate one particular thing. To say, then, 

 that one species is stronger than another is a meaningless statement 

 unless it is specified in what particular respect it excels. 



The term strength, in its more restricted -sense, is the ability 

 to resist stress of a single kind, or the stresses developed in one 

 kind of a constructional member, as strength in shear, strength 

 in compression, strength as a beam, strength as a column. Used in 

 this way, the term is specific and allows no chance of confusion. 



RELATION OF PROPERTIES TO USES. 



There are many properties of wood, such as taste imparted to 

 foodstuffs, odor, ease of working, ability to take finish and to main- 

 tain shape, resistance to decay, etc., which, of course, are not given 

 in the accompanying tables, but which are very important in some 

 uses to which timber is put. In very few instances will strength 

 data of themselves be sufficient to determine the value of a species 

 for a given use. 



There are few, if any, cases in which two species have all the various 

 properties to the same degree or in the same relative proportion. 

 This fact accounts for the special uses of the different species and for 

 the difficulty in finding substitutes for certain species in particular 

 uses. Confusion arises from comparing species for a certain use upon 

 the basis of properties or strength values which are not of first 

 importance in that use. The most important strength values are: In 

 large beams, modulus of rupture, modulus of elasticity, and shear; in 

 long columns, modulus of elasticity and crushing strength in com- 

 pression parallel to grain; in material for spokes, tongues, or poles, 

 ax handles, etc., modulus of rupture, modulus of elasticity, work to 



