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In fluid mechanics, a flow condition (seeturbulent flow) in which local speed and pressure change unpredictably as an average flow is maintained. Common examples are wind and water swirling around obstructions, or fast flow (Reynolds number greater than 2,100) of any sort. Eddies, vortices, and a reduction in drag are characteristics of turbulence. Lowered drag enables golf balls to travel farther than they would do otherwise, and the dimpled surface of golf balls is meant to encourage turbulence in the boundary layer. If swimsuits with rough surfaces help swimmers to move faster, as has been claimed, the same explanation may apply.
This entry comes from Encyclopædia Britannica Concise. For the full entry on turbulence, visit Britannica.com.