Swimmers must fight the effects of friction as they push through the water. Friction is a force that reduces the motion of substances that encounter each other. Swimmers encounter frictional drag in water, just as cyclists and runners encounter frictional drag from the air pushing against them. Minimizing the resistance due to friction is possible for swimmers, but not always necessary.
In simple terms, friction makes it hard to slide through water, forcing swimmers to expend more energy to achieve higher speeds. For example, suppose two swimmers are traveling at the same speed through the water. One is wearing floppy clothing, the other is wearing skin-tight swimwear. The one wearing floppy clothing must work harder to maintain the same speed as the better-equipped companion. While the difference in energy expenditure might not mean much during a short swim, long-distance swimmers are very concerned with minimizing energy expenditure. Maintaining high energy levels helps swimmers move faster and for longer; even a fraction of a second might make the difference between winning and losing a competition.
Swimmers also experience pressure drag. Essentially, a fast-moving swimmer’s body shape displaces water, meaning the water in front of the swimmer is under higher pressure than the water behind. As a result, the faster a swimmer travels, the greater the pressure drag, or resistance applied by the high-pressure area of water in front.
To minimize both friction and pressure drag, swimmers often make themselves as sleek as possible. Shaving body hair, for instance, might reduce drag due to friction, just as perfecting arm and leg movements to minimize body surface area during strokes might reduce pressure drag. Wearing a swim cap or having a shaved head is another way to minimize both friction and pressure drag. The degree of drag reduction you can achieve depends on many factors, but the general consensus is that swimmers move faster through the water when the surface of the body is smooth and when body movements are sufficient to generate force without overly disrupting the water.
Some top-level swimmers wear special swimwear designed to minimize friction with surrounding water. Fabrics are often modeled after the outer surfaces of dolphins, sharks or other fast-moving sea creatures. Low-friction swimsuits might make a difference in high-level competitions, such as the Olympics, but for amateurs, such measures are typically unnecessary. For most people, a more practical solution for swimming faster would be to work on perfecting swimming strokes.
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