Flow is described as laminar when
- A. the fluid particles move in irregular, mixing paths
- B. each fluid particle follows the same smooth path as the one before it
- C. the fluid is at rest
- D. the fluid is compressible
Explanation
In laminar or streamline flow the layers slide over one another without mixing, so the velocity at any fixed point stays constant in time and streamlines never cross. Above a critical speed the motion breaks up into eddies and becomes turbulent, which dissipates far more energy. The Reynolds number is what predicts which regime a given flow is in.