Drag in swimming

Drag is the term used to identify the resistance of water to swimmers' movements through it. That resistance is caused by a difference in pressure between the water in front of and behind swimmers. Objects tend to be pushed from areas of high pressure toward areas of low pressure. Consequently, if the pressure of the water in front of swimmers is greater than the pressure behind, their speed will be decreased unless they can overcome the added pressure by stroking with greater force. The reduction in speed will be in direct proportion to the magnitude of the difference in water pressure in front of and behind the body.

Fundamentals for reducing resistive drag

Water is a 1000 times more dense than air, so when the body moves forward through it, the water resists its movement with a force substantially greater than the resistance of air. That force is resistive drag. Swimmers will accelerate forward so long as the propulsive forces they apply are greater than the resistive drag forces holding them back. They encounter resistive drag as they move forward because they must actually push streams of water molecules out of their way to open a hole in the water for the body to pass through. The resistive drag is directly proportional to the turbulence they create as they swim down the pool and is determined by four factors:

• the space swimmers take up in the water,
• the shape they present to the water,
• limb movements that push water forward instead of backward, and
• the friction between the body and the streams of water that come in contact with it.