1. The problem statement, all variables and given/known data Hi, I am doing physics lab on finding coefficient viscosity of fluids and how it changes by temperature by dropping a marble into fluids, finding terminal velocity, then using stoke's law to find viscosity. (using density of fluid, sphere, sphere diameter etc). The equation is found here https://en.wikipedia.org/wiki/Stokes'_law under Terminal Velocity.... I have just realized something and encountered a problem. For this experiment to work, the fluid at all temperatures should have the same density, however changing the temperature will change the density!!! How can I keep the density constant? Does what I am saying make sense? 2. Relevant equations The equation of stoke's law is found here https://en.wikipedia.org/wiki/Stokes'_law under Terminal Velocity. It is derived when the viscous drag force plus the buoyant force equal the weight of the ball at terminal speed 3. The attempt at a solution Trying to find a way to keep density constant but no success yet!