SCIENTIA.

Why can’t everyone swim like Michael Phelps? There is a combination of sciences that need to be explored to attain the definitive answer to this question. The slight change in the degree of entry into the water from the blocks to the slow push off on the opposite wall may mean the difference between winning and losing a race. We often look at science for the reason things happen, swimming is no different. The physics involved in being a swimmer can assist us in understanding not only why we cannot all win, but how we can all improve.

 

To understand how we can enhance our performances in races, we must talk about the fastest moment in swimming: the dive. Let’s explore the dive into further detail and how someone can go under 5 seconds for 15-meters. The first concept I would like to explore is the position of the swimmer on the blocks. The physics involved in the dive is using chemical energy to move your arms forward, then adding the kinetic energy of the forward direction and the gravitational potential energy of falling, therefore you enter the water faster. These add up to the total energy that launches us forwards. There are many types of race starts, from a grab start to a front-weighted kick start [Ricardo Peterson Silveira, 2018], that swimmers can experiment with to find the best fit for themselves. Ricardo’s paper concluded that there isn’t enough evidence available for us to determine the best race start, however swimmers currently tend to prefer the track starts. In all types of sports involving a track start, athletes that have higher hips on the track tend to have a faster reaction time and a greater horizontal force, [Bezodis, N.E., Willwacher, S. & Salo, A.I.T., 2019] allowing them to push off with greater velocity.

 

Newton’s 2nd Law of Motion, which states that “Forces equals Mass times Acceleration,” [Britannica/E.Gregersen, 2021] tells us that you will achieve a faster acceleration from a greater force. To increase this force, we must use our arms to pull the blocks, whilst swinging in a coupling motion, ending up in a perfect streamline. Using the whole body creates a bigger force than just the legs. Once we have broken the inertia of the start, carrying the momentum into the water is important, as water is denser than air and drastically slows us down. The formula, Momentum equals mass times velocity [Physics Classroom/Tom Henderson] shows us that we have to keep the velocity the same otherwise the momentum will decrease.

 

As we enter the water, it is best for your feet to enter where your hand has entered since your fingertips have already broken the surface tension of the water. The water molecules on the surface of the water have strong attraction towards each other as each molecule is pulling each other from all directions, however molecules on the surface don’t have a pull from all directions so they have a stronger pull from neighbouring molecules [Biolin Scientific/Susanna Lauren, 2020]. This is where a tight streamline would be incredibly helpful. Swimmers may want to flick their hips upwards just before entering the water so that their lower bodies enter the hole created by the upper body, thus minimising the surface area of the body that is in contact with the surface of the water.  Entering the water at the optimal angle of 30 degrees [M.T.Gallivan and T.B.Hoshizaki, 1986] will allow for the best glide phase, close enough to the surface of the water to exit without being too far under the water.

 

The advantage many champion swimmers have is making use of the principle behind Newton’s 3rd Law. Known as “underwater kicks”, “dolphin kicks”, “butterfly kicks” or 5th stroke, swimmers move their lower body in an upward and downward motion underwater after their initial entry into the water. Usually, average swimmers don’t have strong enough underwater kicks, as their upward kicks are just a reset for the downward kick. In Newton’s 3rd Law, it states that “for every action, there is an equal but opposite reaction” [Britannica/E.Gregersen, 2021] so every movement creates an advantage to move faster through the water. Having both a powerful up-kick and down-kick will be useful for your dives and turns, helping you touch the wall before your opponents. 

 

This review discussed the applied theories of physics implemented to analyse the perfect dive. Overall, the perfect dive consists of 3 major concepts: the starting position, the entry, and the underwater kicks. As a rapidly evolving sport, the willingness to apply new theories and new techniques will assist swimmers with improving their ability to be best both in and out of the pool.  

​

Written By: Prin Chantarangkul (Year 12 Student at Bangkok Patana School)

​

Works Cited

Bezodis.N, (2019) ‘The Biomechanics of the Track and Field Sprint Start: A Narrative Review’

 https://link.springer.com/article/10.1007/s40279-019-01138-1#Sec31 

Editors Britannica, (2021) ‘Newton’s laws of motion’

 https://www.britannica.com/science/Newtons-laws-of-motion 

Hadhazy.A, (2008) ‘What Makes Michael Phelps So Good?’

https://www.scientificamerican.com/article/what-makes-michael-phelps-so-good1/ 

Kerchgessner.R, (2016) ‘The Physics of Swimming’

https://aplusphysics.com/community/index.php?/blogs/entry/30558-the-physics-of-swimming/ 

M.T.Gallivan and T.B.Hoshizaki, (1986) ‘Optimization of Swimming Starting Performance’

         https://ojs.ub.uni-konstanz.de/cpa/article/view/1518

PhysicsClassroom, ‘Momentum’

https://www.physicsclassroom.com/Class/momentum/u4l1a.cfm 

Poirier-Leroy.O, (2021) ‘7 Reasons Calaeb Dressel’s Start is the Best in the World’

https://www.yourswimlog.com/caeleb-dressels-start/ 

Real World Physics Problems, ‘Slingshot Physics’

https://www.real-world-physics-problems.com/slingshot-physics.html 

Ricardo Peterson Silveira, (2018) ‘Key determinants of time to 5m in different ventral swimming start techniques’

https://www.tandfonline.com/doi/full/10.1080/17461391.2018.1486460