Intuition might tell us that rough surfaces on clothing would inhibit the speed of an olympic athlete. why is this line of thinking not true in some cases? how can controlled roughness actually promote speed?

When it comes to clothing, roughness could promote proper aerodynamics and/or proper flow of air to and from the athlete’s body. Enough roughness could also lessen the air drag on the athlete’s body thereby reducing the amount of effort that he has to exert to gain the desired speed. 

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