MISCELLANEOUS PROBLEMS. 531 



Strength of Materials. 

 There are three ways by which solid bodies resist force. 



1. Resistance to pressure. 



2. Resistance to stretch. 



3. Resistance to twist. 



RESISTANCE TO PRESSURE. 



The following rule applies to the strength of moderately 

 seasoned white or yellow pine : 



Divide the square of the length in inches by the square of the 

 least thickness in inches ; multiply the quotient by .004 and to this 

 product add I.; divide 5,000 by this sum and the result is the 

 strength in pounds per square inch of the area of the end of the 

 post; multiply this result by the area of the end of the post in 

 inches and the result will be the strength of the post in pounds. 



PROBLEMS. 



1. If a post of half seasoned white pine firmly fixed and equally 

 loaded is 8 inches square and 8 feet long, what weight in tons is it 

 capable of carrying? 



2. A rectangular pillar is 4 by 10 inches and is 12 feet long; how 

 many tons will it carry? 



3. How many tons will a post carry that is 4 by 4 inches square 

 and 15 feet long? 



4. The dimensions of a rectangular pine pillar are 6 by 8 inches, 22 

 feet long; what is the number of tons it will support? 



5. Find the width of a pillar 12 feet long and 12 inches wide, that 

 will carry a weight of 164 tons. 



NOTE As there is a wide variation in the strength of different 

 kinds of timber and also a difference in the strength of different pieces 

 of the same kind of wood, it is a good rule to estimate the load to be 

 carried at 50 per cent of the theoretical load they are computed to carry. 



RESISTANCE TO STRETCH. 



According to King, the tensile strength of materials is given 

 as follows : 



Elm 6,000 per square inch 



Poplar 7,000 " 



Maple 10,000 " 



Oak (white or red) 10,000 " 



White pine 10,000 " 



American Hickory 11,000 



