The Effects of Friction on Swimmers

Friction, which is created when surfaces rub against each other, reduces the speed at which a swimmer can move through the water. Competitive swimmers are constantly seeking ways to reduce frictional resistance or drag. Even if they only reduce their time by a few hundredths of a second, it can mean the difference between winning and losing a race.

  1. Frictional Drag

    • Frictional drag is generated as the swimmer's body collides and rubs against the water. Faster speeds generates more frictional drag, as the collisions between the swimmer and surrounding water molecules increase in force and number. Not surprisingly, frictional drag is greatest between the swimmer and the water molecules closest to the contours of his body. There is also considerably more frictional drag generated when water molecules collide with larger areas such as the front of the body, which is constantly pushing against the water.

    Additional Problems

    • As a swimmer's speed increases, water further away from him also becomes affected. Eventually, the increased turbulence and movement of water around the swimmer creates changes in pressure and forms waves that produce additional forms of drag. These changes ultimately limit how fast the swimmer can go and increase the energy he must expend to maintain speed. It's no surprise that competitive swimmers use a number of different ways to reduce frictional drag in their quest to gain an edge.

    Reducing Frictional Drag

    • A freestyle swimmer can reduce frictional drag by rolling his shoulders from side to side with each stroke. This turns his body and minimizes his frontal area, allowing less of it to hit the water as he is moving through it. The effects of frictional drag means that having a larger, more muscular body is not necessarily a desirable characteristic for a swimmer. Many fast swimmers have smaller frames.

    External Modifications

    • Another strategy for reducing frictional drag involves the modification of external surfaces to make them smoother, with fewer rough areas to bump against water molecules. Wearing a swim cap over the hair, shaving body hair before a race, and wearing a closely-fitting swimsuit are all methods to reduce drag that have been used for years by competitive swimmers. Specially designed hydrodynamic swimsuits that mimic sharkskin is a more recent development that has quickly been embraced by elite swimmers.