<P> If the particles are falling in the viscous fluid by their own weight, then a terminal velocity, also known as the settling velocity, is reached when this frictional force combined with the buoyant force exactly balance the gravitational force . The resulting settling velocity (or terminal velocity) is given by: </P> <Dl> <Dd> V s = 2 9 r 2 g (ρ p − ρ f) μ (\ displaystyle V_ (s) = (\ frac (2) (9)) (\ frac (r ^ (2) g \ left (\ rho _ (p) - \ rho _ (f) \ right)) (\ mu))) </Dd> </Dl> <Dd> V s = 2 9 r 2 g (ρ p − ρ f) μ (\ displaystyle V_ (s) = (\ frac (2) (9)) (\ frac (r ^ (2) g \ left (\ rho _ (p) - \ rho _ (f) \ right)) (\ mu))) </Dd> <Ul> <Li> V is the particles' settling velocity (m / s) (vertically downwards if ρ> ρ, upwards if ρ <ρ, </Li> <Li> r is the Stokes radius of the particle (m), </Li> <Li> g is the gravitational acceleration (m / s), </Li> <Li> ρ is the density of the particles (kg / m), </Li> <Li> ρ is the density of the fluid (kg / m), and </Li> <Li> μ is the (dynamic) fluid viscosity (Pa s). </Li> </Ul>

Glass tube filled with liquid by suction used for measuring