Transportation on Water 



343 





Exercise. What is the weight of a pine timber 12 inches in each 

 dimension and 10 feet long? How deep would it sink in water when 

 resting on one side ? Suppose it were kept stand- 

 ing in a vertical position in water (Fig. 116), how 

 deep would it sink before the pressure from below 

 would be sufficient to support it ? What fractional 

 part of the timber is out of water ? 



Consult the table of relative densities and that 

 of weight per cubic foot of substances in order to 

 answer these questions. Which of the woods, 

 pine, spruce, oak, cedar, and lignum vitas, would 

 you select for lightness in making a boat? Why 

 is cork well adapted for use in lif e preservers ? As 

 a float for fishing nets and lines ? Would a piece of 

 iron float on mercury ? on molten glass ? 

 your answers. If you had no other information 



m 



8(62.6) 



500 IBS . 



FIG. 116. Pres- 

 . sure varies with the 

 Explain depth ( d i a g ram ). 



than is presented in this table, would you judge that materials for 

 building boats must be limited to woods with densities less than that 

 of water? 



WEIGHT OF COMMON SUBSTANCES PER CUBIC FOOT 



Ash, dried 43.7 



Ash, green 52.8 



Beech 53.2 



Cedar ...... 35. 



Cork 15. 



Lignum vitae .... 83.3 



Oak 53 



Maple 46. 



Pine 29. 



Spruce 31.2 



Walnut . 41.6 



Iron, cast 449. 



Aluminum 165.6 



Copper 555. 



Lead . . . 



Tin . . . 

 Zinc . 



Steel . . . 

 Iron, wrought 



Brass . . 

 Water 



709.7 

 455.8 

 431.3 

 490. 

 489. 

 528. 

 62.5 



TABLE OF RELATIVE DENSITIES 



Water 1.00 



Water, sea .... 1.03 



Pine 5 



Oak 8 to 1.17 



Cedar 4 



Cork .25 



Lead 11.4 



Mercury 13.6 



Gold 19.3 



Iron 7.5 



Aluminum . . . . 2.65 



Glass . ... 2.5 



