Relating to Physics: the Physics Behind Competitive Swimming

            Although, I was a competitive swimmer for fifteen years, I never really considered the physics behind my sport and the techniques my coaches encouraged me to implement in order to improve. In swimming, there are four strokes: butterfly, backstroke, breastroke, and freestyle. Below I have included one of the fastest swimmers of all time, Michael Phelps doing the butterfly stroke, which also happened to be my stroke when I swam.

 

         When one is swimming one must consider the forces acting on a swimmer. As with any object, a human body displaces water creating an upwards buoyancy force that allows us to stay above the water and not sink. A thrust force is created by a swimmer using their arms to pull themselves forward in the water by displacing water behind them as well as kicking. The drag force exists as the swimmer is moving through a fluid of water. One can determine the buoyancy force by equation: F-b= pgV where p is the density of the water and V is the volume of water displaced by the object. Additionally, one can find the drag force of a swimmer by the equation F-drag= (1/2)pACv^2 where p is the density of water, A is the cross sectional area, C is the drag coefficient, and v is the velocity. To maximize their velocity, professional swimmers try to minimize both their cross sectional area by changing how they move their arms and rotate their head to prevent a large cross sectional area exposed to the water. Essentially, a swimmer wants to be like an arrow with a minimum amount of cross-sectional area and therefore the drag force. Swimmers also try to minimize the force of drag by decreasing their drag coefficient by shaving their bodies and wearing wet suits. In doing so, a smaller force of drag allows for a higher net force forward by the same force of thrust the swimmer is able to produce. Additionally, I realized because swimmers are doing work on the water to overcome this force of drag, which is a non-conservative force, heat is lost to the pool. This is why pools are warmed by people swimming and require temperature maintenance.

         Bernoulli’s Equation can also be applied to swimming:

 

P1 + 1/2ρv1^2 + ρgh1 = P2 + 1/2ρv2^2 + ρgh2.

 

For example, one can see how when a swimmer swims by diving under the water their pgh component increases such that as they rise above the water their potential energy under the water is converted to kinetic energy, which allows them to swim forward and propel out of the water at a faster speed. This makes sense to me because it explains some of the technique behind breastroke and butterfly. In these strokes, the swimmer must dive under and come up to breathe. By doing so, one can convert their potential energy from diving forward under the water into kinetic energy to increase the speed of swimming.

 

 

 

 

Link for first photo: https://www.olympicchannel.com/en/stories/features/detail/michael-phelps-olympic-medals-record-how-many-gold-swimmer-world-record/

For more information on the physics of swimming: https://www.real-world-physics-problems.com/physics-of-swimming.html#:~:text=By%20moving%20his%20or%20her,the%20swimmer%20through%20the%20water. (link to second photo)

https://www.wired.com/2016/08/wanna-swim-like-ledecky-take-dive-physics-drag/