No-slip condition
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In fluid dynamics, the no-slip condition states that fluids have zero velocity at boundaries.
The fluid velocity at all liquid–solid boundaries is zero. In other words, the outermost molecule of a fluid sticks to surfaces past which it flows. The no-slip condition gives rise to the velocity profiles of a flowing fluid. The velocity profile of a fluid in a pipe has zero velocity at the pipe wall, a continuous increase in velocity moving towards the center of the pipe, and maximum velocity at the center of the pipe.
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[edit] Physical justification
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[edit] Exceptions
As with most engineering approximations, the no-slip condition does not always hold in reality. For example, at very low pressure (e.g., at high altitude), even when the continuum approximation still holds there may be so few molecules near the surface that they "bounce along" down the surface.
