Saturday, June 18, 2011

Coefficient of Viscosity

It has been observed that forces of friction (f) between two layers each having area ‘A’ sq. cm, separated by distance ‘dx’ and having velocity difference of ‘dv’ cm/s is given by:
f µ   A dV/dx
Or   f =   ŋ A dV/dx 
Where ŋ  =  co-efficient of viscosity (k/as eta)
& dV/dx = velocity gradient.
If dx  =  1cm,   A  =  1cm2   &   dv  = 1cm/s
Then    f  =  ŋ
Thus,  “co-efficient of viscosity may be defined as the forces of friction required to maintain a velocity difference of 1cm/s between two parallel layers of a liquid 1cm apart and each having an area of 1cm2.”
UNITS OF VISCOSITY
f   =   ŋ A  dV/dx
ŋ   = (f/A) (dx/dV)
=   (dynes × cm)/(cm2 × cmsec-1)  =    dynes cm-2 sec.
1 dynes cm-2 sec = 1 poise
IN S. I. UNIT                  
n   =  (f/A) (dx/dV) = N × m /m2  × ms-1  =N.m-2s.

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