The ultracentrifuge method for determining the molecular 
weights of proteins was developed by svedberg.

in this method protein molecules are subjected to 
gravitational forces greater in magnitude than thermal 
forces whereby causing them to diffuses.protein molecules 
are larger in size called macromolecules.
under high centrifugal forces these molecules can be made 
to sediment towards one end of a centrifuge tube.
The equation derived by svedberg for the molecular weight 
of a protein is

M=RTS/D(1-Vp)
where  R=gas constant
T=absolute temperature
s=sedimentation constant
D=diffusion constant
V=partial specific volume ofprotein
p=density of solvent


PRINCIPLE OF ULTRACENTRIFUGE IS "For most proteins however 
the value of V is in the range of 0.70 to 0.75".