The type of liquid flow is situation-dependent. This explains why a bacterium in water experiences laminar flow whereas we don’t. It is a consequence of the amount of force exerted by us or the bacterium.
Looking at equation 5.5 we can understand why.
f(viscous critical force) = η^2 / ρm
η units are Pa.s
ρ units are kg.m^-3
We look at the effect of applied forces with the dimensionless ratio F(applied)/f(crit)
F/f(crit) = Fρm / η^2
For a large ratio value you can see that the equation will be dominated by the density and therefore inertial effects (proportional to mass). This results in Turbulent Flow.
For a small ratio it is the viscosity and thereby the frictional effect that dominates. Result: Laminar Flow.
Obviously if you apply enough force you can also create turbulent flow from a very viscous liquid. Which is one way a bacterium can feed, by using a burst of force to create turbulent flow to capture its food. Whoever said strength isn't everything obviously wasn't a bacterium.