function [rt1, rt2]=f_buoyantsto(rhoS, rhoF, d, mu, g)

%* f_buoyantsto(rhoS, rhoF, d, mu, g)  
%  computes maximum rise rate of a sphere due to buoyancy
%  assuming no turbulence
%
%  input variables:
%  rhoS:	density of spherical object, kg/m^3
%  rhoF:    density of fluid. kg/m^3
%  d:           diameter of sphere, m
%  mu:      viscosity of fluid through which sphere is rising, Pa s
%  g:		acceleration due to gravity at this location, m/s^2
%
%  return variables:
%  rt1:		rise speed  m/s
%  rt2:     Reynolds number

%* compute rate of vertical rise 
rt1 = d^2 * g * (rhoS-rhoF) /mu /18;	
rt2=abs(rhoF*d*rt1/mu);    % Reynolds number test