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May the Force Not Be With You

Swimmers not only compete against each other but against drag force. Fluid dynamics is the science of dealing with the pressure of fluid flow. In competitive swimming it’s the force that resists the motion of a body moving through the water.

Thrust pushes the swimmer forward and drag is the resistance of the water to the motion of the body. According to Dr. Timothy Wei, “It’s conceptually the exact same problem as an aerodynamicist studying an airplane. They put an engine on an airplane to push the airplane forward and the air is resisting the motion.” Basically, the swimmer is the engine in the pool, and the water is resisting the motion.

 Three Types of Drag

Frictional Drag: this is the dominant drag force of the water along the sides of the swimmer’s body, making it harder to move forward.

Pressure Drag: as the swimmer picks up speed, this is the drag force at the swimmer’s head as the swimmer propels forward through the water.

Wave Drag: Swimming creates waves in the pool causing a barrier wave that the swimmer must constantly push through.


To fight drag forces, swimmers use fluid dynamics to maximize thrust: cupping the hands, churning the arms, kicking hard, keeping the head down, and making the body as narrow an object as possible in the water (streamlining) to efficiently push as much water as possible behind them.

 Missy Franklin, multi-medal swimmer at the 2012 Olympics, says her size 13 feet are hard to find shoes for, but in the pool she uses them as flippers to propel her. With encouragement, passion, and proper technique, swimmers can battle drag force, using their bodies (no matter what size) as engines.

The above blog post was derived from a recent SIKids blog.


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