12 



AXP ITS APPLICATIONS 



Putting / s = [M 'y-, the coefficient /u, is termed the Coefficient of Viscosity. 1 



ill/ 



The value of this coefficient varies with different fluids, and varies with 

 temperature for any particular fluid. 



For water, experiments by Poiseuille indicate that it follows the law 



-00003716 



~ -4712 + -01435 T + "0000682 T 2 



where T is in degrees F., and the corresponding value of the distortive 

 stress f, is given in pounds per square foot. Using the Fahrenheit scale 

 ami taking the poundal and the foot as units of force and space, this 

 formula becomes 



-001197 



~ '4712 + -01435 T + '0000682 T 2 ' 

 With the pound, foot, and degree Centigrade as units we get 



00003710 



1 + -03368 T + -000221 T 2 

 while using the poundal, foot, and degree Centigrade this becomes 



_ -001197 



1 + -03368 T + -000221 T 2 ' 



In C. G. S. units, the unit of force being taken as the weight of 

 1 gramme, and the temperature in degrees Centigrade, we have 



= -0000181 



" + 1 -03308 f+ -000221 T 2 ' 



The following table indicates the values of //, for water corresponding 

 to different temperatures,/, being expressed in pounds per square foot. 





Temperature. 



Kxpre-setl <limensionally we have /* =/ 8 ^ |f = stress -f- 



mass x acceleration 



But stress 



_ force 



area nrr 



.'. /u is of dimension 



/ 



space 



M 



r LT*- 



M 



stre ss x tinn 



