# Macromolecules (Thermodynamics)

1. Apr 20, 2009

### Slepton

1. The problem statement, all variables and given/known data

A dilute solution of macromolecules at temperature T is placed in an untracentrifuge rotating with angular velocity w. The centripetal acceleration w2r acting on a particle of mass m may then be replaced by an equivalent centrifuge force mw2r in the rotating frame of reference.
a) Find how the relative density $$\rho$$(r) of molecules varies with their radial distance r from the axis of rotation.
b) Show quantitatively how the molecular weight of the macromolecules can be determined if the density ratio $$\rho1$$ / $$\rho2$$at the radii r1 and r2 is measured by optical means.

2. Relevant equations

F = mv2/r

density = mass /volume

3. The attempt at a solution