Physics can be applied to every aspect of swimming. Before even entering the water, swimmers model free fall and angled projectile motion as they dive off the starting blocks. U.S. Masters Swimming states that diving at a 45 degree angle maximizes the speed and distance of the dive. Competition suit brands, such as Speedo and Arena, have to be knowledgeable about the physics of water resistance in order to produce their extremely tight and specially-designed "Fastskins" that are known for helping swimmers achieve best times by strategically compressing their bodies to maximize speed and to minimize water resistance. However, the best examples of physics found in swimming are found when applying Newton's 1st, 2nd, and 3rd laws to the sport.
Newton's 1st Law states that an object at rest tends to stay at rest and an object in motion tends to stay in motion, at constant velocity and in a straight line, unless acted upon by a net force. It is also known as the Law of Inertia. When swimmers dive into the water, they hold themselves still in a horizontal streamline position for a few moments before starting their kick. Water resistance acts as the net force, which quickly begins to slow swimmers in streamline position. This is when they know to start kicking because, otherwise, the water will end up stopping them. Furthermore, taller and bigger swimmers have greater inertia, so their speed off the block and speed of flip turns are naturally slower. Nevertheless, larger swimmers are often stronger and therefore able to produce enough of a force to dive and turn quickly.
Moving on, Newton's 2nd Law says that the net force on an objects is equal to its mass times its acceleration. The more force a swimmer can apply, the faster he/she will go. It is common, especially in longer events, to see swimmers start out strong, then slow down and start to look tired, and finally speed up at the end for a strong finish. As swimmers get tired, they begin to produce less force, thereby beginning to decelerate. Towards the end of a race, knowing they are in the home stretch and are going to be able to live to finish the event, swimmers muster enough force to accelerate. During practice, a common set is one involving descending times, which exhausts swimmers, since they have to increase the force they are applying to be able to accelerate.
Finally, Newton's 3rd Law states that all forces come in pairs that are equal in magnitude and opposite in direction. It is commonly said as "for every action, there is an equal and opposite reaction." This law is the most obvious to observe when watching a swimmer. As the hand and arm push the water backwards, the water pushes forwards with a force that is of equal magnitude. This motion keeps the swimmer afloat and allows him or her to move forward in the water. Every stroke involves the swimmer pulling down and back in order to move up and forward.
Clearly, physics is exemplified everywhere in the sport of swimming. Physics explains why certain stroke techniques are more effective and why some swimmers are faster than others. Even Michael Phelps' success can be credited to his expertise at applying Newton's first three laws to his sport. After reading this, maybe we will see you in Tokyo 2020 with the other great physicists who call themselves the USA Olympic Swim Team!
The pages of APlusPhysics.com, Physics in Action podcasts, and other online media at this site are made available as a service to physics students, instructors, and others. Their use is encouraged and is free of charge. Teachers who wish to use materials either in a classroom demonstration format or as part of an interactive activity/lesson are granted permission (and encouraged) to do so. Linking to information on this site is allowed and encouraged, but content from APlusPhysics may not be made available elsewhere on the Internet without the author's written permission.
APlusPhysics.com, Silly Beagle Productions and Physics In Action materials are copyright protected and the author restricts their use to online usage through a live internet connection. Any downloading of files to other storage devices (hard drives, web servers, school servers, CDs, etc.) with the exception of Physics In Action podcast episodes is prohibited. The use of images, text and animations in other projects (including non-profit endeavors) is also prohibited. Requests for permission to use such material on other projects may be submitted in writing to firstname.lastname@example.org. Licensing of the content of APlusPhysics.com for other uses may be considered in the future.