U.S. swimmer Missy Franklin is one of the top medal contenders at the 2012 Summer Olympics. Just as engineers design planes and boats to be more aerodynamic, Franklin will need to master the basic principles of fluid dynamics in order to be the fastest swimmer in the pool. "Science of the Summer Olympics" is a 10-part video series produced in partnership with the National Science Foundation.
Missy Franklin and Fluid Dynamics
LIAM McHUGH, reporting:
Just 17 years-old, Missy Franklin is already a swimming phenom. In 2011, she set a world record in the 200 meter backstroke, and dominated at the World Championships, bringing home five medals - three of them gold - success she hopes to continue at the 2012 Summer Olympics.
MISSY FRANKLIN (U.S. Swim Team): Being in the water just is so natural for me and it comes like walking on land. I absolutely love what I'm doing and I think that gives me huge advantage.
McHUGH: One of Franklin's biggest advantages in the pool is her size - six foot one with strong shoulders and long limbs that allow her to maximize thrust and overcome drag, two key components of fluid dynamics.
Dr. TIM WEI (University of Nebraska-Lincoln): Thrust is what pushes the swimmer forward and drag is the resistance of the water to the motion of the body.
McHUGH: Timothy Wei is dean of the College of Engineering at the University of Nebraska – Lincoln, and has been supported by the National Science Foundation. Wei has applied his knowledge of fluid dynamics to the sport of swimming, helping elite swimmers optimize their strokes and move faster through the water, much as an engineer designs cars, boats and airplanes to go faster and be more aerodynamic.
Dr. WEI: It's conceptually the exact same problem as an aerodynamicist studying the design of an airplane. They put an engine on an airplane to push the airplane forward and the air is resisting the motion. So the swimmer doesn't have engines. The engines are their body parts. And so they try and move their body parts in as efficient a way as possible to push water backwards.
McHUGH: From the moment the race starts, Franklin is in a battle against three types of drag. Frictional drag, sometimes called viscous drag, happens when friction pulls the water next to her body along with her, making it harder to move forward.
Dr. WEI: That's the frictional effect of the water as it goes by the body. That's really more the dominant drag force in a swimmer.
McHUGH: As she picks up speed, Franklin also encounters pressure drag as the water moves around her head and body and doesn't reattach until past her feet, creating a pressure difference.
Dr. WEI: You'll have high pressure on the front, low pressure on the back. And what you end up with is there is a pressure difference between the front and the back. So that is a force which is pushing the object backwards.
McHUGH: Franklin also encounters a third type of drag called wave drag. As she moves forward, some water is pushed in front of her creating a wave barrier to her progress.
Dr. WEI: Just like a speedboat has to climb over the top of that bow wave, a swimmer has to swim over the top of that.
McHUGH: Franklin counters these three types of drag with thrust, the propulsive force that moves her through the water.
Dr. WEI: The whole process of swimming technique is getting your body to move in as efficient a way as possible so you maximize the thrust. You take advantage of all the different kinds of thrusts that are available to you, which is the arm motion and the kicking motion.
McHUGH: Franklin creates thrust by cupping her hands and churning her arms in an effort to push as much water as possible behind her. She also kicks hard with her size 13 feet, what she calls her own personal flippers.
FRANKLIN: Something about my last part of my race just really gets me going and I just move my arms and legs as fast as I possibly can.
McHUGH: In addition to thrust, Franklin relies on technique to help reduce her drag. Her stroke and body position are engineered to minimize her contact with the water, something swimmers call streamlining.
Dr. WEI: That's basically to just try and make yourself as thin and narrow an object as possible. Think about an airplane. You don't stick big things off the airplane wing that's going to block the flow and so you're going to do the exact same thing as a swimmer.
FRANKLIN: Each swimmer's stroke is so different, but just everything comes together - the way you put your hands in, the way you do this, the way you do that. Everything just makes your stroke unique.
McHUGH: Using streamlining and thrust to counter drag, Franklin takes advantage of the principles of fluid dynamics to reach for Olympic gold.
A force may be thought of as a push or pull in a specific direction. A force is a vector quantity, so a force has both a magnitude and a direction. When describing forces, we have to specify both the magnitude and the direction. This slide shows the forces that act on an airplane in flight.
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