Fluid Mechanics
Transition from laminar flow to turbulent flow is aided by the

Surface roughness and curvature (i.e.sharp corners)
All of these
Pressure gradient and the compressibility of the flowing medium
Vibration

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Fluid Mechanics
A stream line is

Always the path of particle
Drawn normal to the velocity vector at every point
Fixed in space in steady flow
A line connecting the mid points of flow cross-section

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