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.
No comments:
Post a Comment