what does awim have to do with science

The science of pond

by Chris Woodford. Last updated: August 15, 2021.

Humans evolved from bounding main creatures but—looking at our bodies—y'all'd never know information technology. We couldn't be less well suited to moving through water if we tried. We don't float too well, can't breathe for long beneath the surface, and rapidly tire as we thrash through the waves trying to move ourselves forth; in a straight race with a dolphin or a shark, yous'll always come last!

But there's ane big advantage we humans practice take: we know nigh science. We empathise how forces work and how to use them to our advantage. If you've never thought well-nigh swimming every bit a scientific discipline, at present's the time to kickoff. Apply some scientific thinking and you'll notice y'all can swim much more than finer. If y'all're a nervous nonswimmer, thinking almost the solid science that keeps people afloat tin requite yous enough confidence to break through your fear. And then what are we waiting for? Let's take the plunge—with a closer look at the scientific discipline of swimming!

Photo: Swimming takes humans back from the land to the body of water—or the pool! You have to apply forces to move yourself through the water and other forces tedious you down. Sympathize those forces and you tin can swim much more effectively. Photo past R. Jason Brunson courtesy of U.s. Navy.

Contents

1. What is pond?
2. Newton's laws of swimming
3. Minimizing your drag
4. Swimming efficiently
5. Floating and buoyancy
6. Question: Does pond warm the pool?
7. Find out more than

What is swimming?

That sounds like a piddling question, just information technology helps to be articulate.

Swimming is moving your body through water (a moderately pasty fluid) that'due south either still (equally in a swimming puddle), turbulent (every bit in the ocean), or somewhere in betwixt. If you're swimming completely under the surface (for example, scuba diving), y'all're moving through relatively still water; other times, y'all're going to exist moving along at the more turbulent interface between air and water, with your legs, arms, head, and body moving from one chemical element to the other and back again, speeding up or slowing downwards as they cantankerous the edge.

Photograph: Fifty-fifty the all-time swimmers take to move along the inclement interface between air and water. It's the most inefficient place to swim, simply the but place you can do it if you need to breathe air. Photo by Michael R. Holzworth courtesy of US Navy.

Water versus air

Before we tin can sympathise the science of pond, information technology helps to remember that air (a gas) is very different from water (a liquid). The biggest difference is that water is much more dense (the same volume of it weighs much more) and pasty (in other words, thicker—in the same way that treacle is more viscous than water).

Artwork: Water is much more dense than air (has many more molecules per unit of volume), which is why it'due south harder to swim through and why it feels common cold, even when information technology's the aforementioned temperature as the air in a higher place. Getting into "cold" water is like touching "cold" metal: both feel cold considering they conduct (and steal) heat from your body very finer.

The divergence between air and water makes a huge difference to how we tin can move on air and state. When you walk on land, the master thing your trunk has to do is piece of work confronting gravity (lifting your legs, swinging your artillery, and keeping y'all from toppling over through constant adjustments of your balance) and a lilliputian bit of friction where your shoes meet the basis. If yous move more chop-chop (say, on a bicycle), air resistance becomes a more important forcefulness than gravity; unless you're walking into a really stiff wind, you barely notice the air while y'all're walking. When you're in the water, gravity is much less of import considering your buoyancy (tendency to float) largely cancels information technology out. The main force you take to recall about as a swimmer is elevate—water resistance. We'll come to that in a moment.

Other differences between water and air are important if you swim outdoors, specially in the wintertime months: because water is much more dumbo than air (more than precisely, considering it contains many more molecules per unit of book, and those molecules are bonded together), it removes oestrus from your torso about 25–forty times faster than air at the same temperature. (That's why surfers and "wild" outdoor swimmers tend to article of clothing wetsuits to avoid hypothermia, the very dangerous cooling of the torso's core that can kill y'all.) Considering water is so much denser than air, it takes a much longer fourth dimension to warm upwards. That'southward why the ocean temperature typically lags backside the land temperature by ii–three months in countries such as the East Coast of the United states of america and the UK (where the sea is often warmest in September).

Newton'southward laws of swimming

If yous honey science merely pond scares y'all, you lot'll find it very helpful—equally I did when I was learning to swim—to think most Newton's three laws of motion. Among the most central rules of physics, these 3 bones principles are enough to explicate completely the motility of almost every single object y'all're ever likely to come beyond.

The first law outlines the concept of inertia. Information technology says that things stay still or motion steadily (at the same speed) unless something pushes or pulls them (unless some kind of a strength is applied). The 2nd and third laws are of more involvement. The 2d constabulary explains the connection between force and acceleration: if you lot push or pull something, it starts moving (if it was nevertheless to begin with) or goes faster (if it was moving already); the bigger the force you utilize, the more acceleration you get; the longer you apply the force, the bigger the alter in momentum yous can accomplish.

Where swimming is concerned, the 3rd police is perhaps the near important. It says that when you apply a forcefulness to an object, the object returns the favor and applies an equal strength to you—in the reverse direction. This law is often called action and reaction and it's the simplest way for a scientific non-swimmer to brand sense of the h2o. You lot probably know already that if yous kicking backward against the wall of a swimming pool, you shoot frontward through the water. The same applies to bodily pond strokes. Simply speaking, if you want to swim forwards through water, you have to pull water backward with your hands. If you want your body to stay up, floating on the surface, yous demand to boot down with your legs. If you lot're swimming along and y'all desire to end all of a sudden and stand upward, you can pull your hands downwards in front of you (in a kind of round move—a bit like bowing down) and your legs will swing downward backside yous, and then yous land in an upright position on your feet. Master these bones moves—elementary applications of Newton'southward 3rd law—and you lot'll notice you'll be able to swim easily and end confidently whenever you need to.

Photo: Isaac Newton tells united states nosotros have to pull water backward to get forward, as this swimmer is doing by using his outstretched hand and forearm as a paddle. This part of the stroke is called the catch and pull. Photo past Alan D. Monyelle courtesy of The states Navy and Wikimedia Commons.

Minimizing your drag

Photo: Speed cyclists realize they accept to minimize drag because they can feel the air pushing hard against them. Even though h2o is "thicker" and swimmers feel the elevate of the h2o much more, they don't e'er realize the importance of minimizing drag.

Lots of other scientific factors make a big difference to how well y'all can move through the h2o. In one case yous've mastered the basic science of swimming, minimizing your drag in the h2o is the next step: that will assist you swim faster and for longer, using the minimum amount of energy in the procedure. Many beginners don't really understand this, simply it'southward exactly the aforementioned as cycling: in the same way that cyclists have to minimize the expanse they present to the wind (crouch forward, put their arms in, and generally streamline themselves), so swimmers have to create as little resistance to the water as they peradventure can. In exercise, this ways making your body completely horizontal, so (in the example of forepart crawl) your caput is well down in the water rather than poking upward with your trunk sloping downwards behind it. (That'southward why you have to learn how to exhale in at the side and breathe out underwater.) You can likewise minimize elevate by slicing your hand in and out of the water to make your strokes and, in front crawl, y'all can learn to swivel (rotate) your trunk every bit you swim from side to side. And it helps to pin your ankles and point your toes like a ballerina so your feet aren't dragging in the water as brakes.

Your own body shape besides plays a part in how much elevate y'all create, and a well-fitting swim suit or moisture suit can make a big departure. (Y'all'll have noticed that peak male swimmers always wear tight-fitting "jammers" or skimpy trunks instead of baggy boardshorts with cool, billowing pockets.) Some other affair that affects drag is the extent to which y'all disturb the water as you swim (the more turbulence you lot create, the more you'll discover elevate is a trouble). Similarly, if you're swimming something like triathlon and you can find a slap-up place in the slipstream of someone in front end, you'll minimize drag only similar a cyclist slipstreaming a car or a bus. Just fifty-fifty if you work hard to minimize all these factors, you'll even so typically use about four times more free energy swimming a certain altitude than you would would running the same length. Swimming is hard work! [1]

It'due south worth noting that sea-h2o is harder to swim in than pool water, for several reasons. First, except on beautifully at-home summer days, the bounding main is most ever more turbulent, so your torso doesn't slice through the h2o similar a dolphin. Sea-water is likewise more dense than freshwater because of the salt information technology contains, and that makes it slightly more than viscous as well. And cold h2o (in the ocean) is more viscous than hot water (in a heated puddle); the viscosity of water at 10°C (50°F) is twice that of h2o at xl°C (~100°F). [ii] If the water is peculiarly cold, your body will shiver to keep you warm, and that will apply up more oxygen and energy. All these things make a common cold body of water swim a tougher proffer than a swim in the heated pool, but the upshot is that your body is working harder and getting more practise.

Unlike with cycling or sprinting through air, it's hard to built up any momentum when yous're pond: though you certainly glide for a short time, water resistance will yet bring you chop-chop to a halt. What nosotros have hither is the first law of motion in action. If water were every bit calorie-free equally air but you lot could still float and swim through it, you could stroke for a while and then rest, allowing your momentum to keep you moving forward (much as y'all can stop pedaling on a bicycle every so often). But the force of the water pushing against you brings you rapidly to a residual. You'll likewise experience inertia when you try to change direction: since velocity is speed in a item direction, changing direction means changing velocity—and information technology requires yous to employ a forcefulness, even if you swim at constant speed. If you're doing front crawl and you decide you want to plough around in a semi-circle and go back the manner you lot came, information technology's actually quite difficult to change the direction of your motion without stopping and reversing or doing a somersault.

Swimming efficiently

"Professor Hildebrand celebrated his 77th birthday past swimming a half mile in 22 minutes. He said, "I used swim fins and webbed gloves considering a man of intelligence should employ his power efficiently, not just churn the water.""

Joel H. Hildebrand, The New York Times Obituary, May 3, 1983.

Swimming is superb aerobic exercise (vigorous exercise that really pumps your heart and lungs) and very tiring; the ii things are, of class, connected. You tin can swim farther for longer by swimming more efficiently, which ways using equally little free energy as possible for each stroke past minimizing drag, and getting equally much forward propulsion as y'all tin can.

With front crawl, the object is to extend your hand equally much as you can and bring it dorsum as far as possible, dragging every bit much water back (with a cupped hand and a bent forearm) as yous peradventure can. (Pond teachers call this two-function process the "catch" and "pull.") If you make a long, complete stroke with a proper follow-through, you're applying your pulling forcefulness for longer and each stroke volition count for more. Yous can come across this from Newton's second law of motion, which is often written:

strength = mass × acceleration
F = m a

Since acceleration is velocity divided by fourth dimension, it's too true that forcefulness is equal to the charge per unit of change of momentum:

F = mv / t

and that:

force × fourth dimension = mass × velocity
F t = m v

To put information technology some other way, if you lot want to produce the biggest possible alter of momentum, you lot need to use your strength (pulling back on the h2o) for as long as possible—with as long a stroke every bit possible and a practiced, complete follow-through. It'due south besides worth remembering that the human body is a machine (in the strict scientific sense of that word): our limbs work like levers, pivoted at our joints (which are effectively fulcrums), multiplying strength or speed. When you lot're doing front end crawl, information technology's important to reach forward and pull your arm backward as much every bit you possibly can. You go more leverage on the water that way and the force you lot create pulling backward volition give you lot more than force to go forrard. A good follow-through also decelerates your limbs more than slowly, and reducing the dispatch reduces the forcefulness they feel, reducing the likelihood of pulled muscles and other injuries.

Photo: It's important to reach forrard and extend your arm every bit much as possible. Photo past Joseph Yard. Clark courtesy of US Navy and Wikimedia Commons.

The conservation of momentum tells us that the momentum you requite your body, going frontwards, is the same as the momentum you give the water, pulling astern. That implies that you demand to pull as much water backward as you lot mayhap can with each stroke. Cupping your mitt helps; keeping your elbow loftier every bit you pull back helps too, so your forearm works as a kind of paddle, and you pull back an entire arm's worth of water rather than a mere handful. Y'all'll find this is much harder and more than tiring to brainstorm with, which is a good sign: information technology shows you lot're creating much more force.

Energy and power

It takes energy to push your body through the water—and your body loses the same corporeality of energy in the process. The rate at which something uses energy is called power. According to an interesting weblog post in Wired by physicist Rhett Allain, champion swimmers can briefly reach a power of 1200 watts (the maximum power of a clothes washing machine or a very powerful vacuum cleaner), which is similar to what a champion cyclist can achieve for brusk periods, pumping abroad apartment out. In his volume The Human Motorcar, British zoology professor R. McNeill Alexander quotes power figures for pond that are in the hundreds of watts. [3] This is consistent with the power that meridian cyclists routinely generate (and it'southward also similar to the figure in the calculation in the box at the end of this commodity.)

Nautical chart: Top swimmers (and cyclists) tin can produce several hundred watts of ability, which is almost twice as much every bit the rest of the states. This chart shows how that amount of power compares to some familiar everyday appliances. In theory, a swimmer could power three LCD TVs, iv old-fashioned lamps, or 20 energy-efficient lamps.

Floating and buoyancy

Things float because when nosotros place them in water, the pressure level of the water underneath them pushes up and supports them; in other words, water pressure pushing upward balances weight (the force of gravity) pulling downward. That's one of the reasons why we swim in a horizontal position: spreading the body flat makes it piece of work more than like a raft, so there'due south more than upthrust from the water below. You probably know that it's much easier to float on your back than standing directly upwards, when y'all need to "tread water" (kicking and push your arms downward to create an up strength that stops you sinking).

Photo: Our bodies are surprisingly buoyant, simply nosotros float better in some positions than others. This swimmer is practicing a survival technique called the prone or "dead man's float," which helps y'all bladder in water for longer and conserve energy. Photograph past William R. Goodwin courtesy of US Navy.

A non-swimmer's biggest fearfulness is sinking under the h2o and drowning, but it's much harder to sink when you're swimming than you lot might suppose. (Unlike when you accidentally fall into a river, where y'all're more probable to sink and drown because your clothes get wet and cease you swimming properly; factors such as the coldness of the water also play a part.) Depending on your torso type (how big you are, how much you weigh, how big your lungs are, how fat you are, and and so on), yous may be surprisingly buoyant: you lot might find information technology quite hard to sink even if yous desire to. It's fairly well known that fatter people are more buoyant than skinnier ones, and that's considering fat is less dense (more buoyant) than muscle. Wearing a wetsuit (made from a constructed rubber chosen neoprene, which traps air bubbles inside it) makes you even more buoyant, which is why scuba divers typically take to wear weights to make them sink.

Is it amend to float or to sink? If you're a boat, it's certainly amend to do one or the other! Unfortunately, about boats do a bit of both: they crash and drag direct through the waves—in the very turbulent interface between the air and the h2o. The fastest boats are hydrofoils and hovercraft (which aim to lift themselves clear of the waves) and submarines (which sink beneath them). If you're a swimmer, neither of these is really an option. Nosotros can't choose whether to sink or float: we have to drag through the water. Nevertheless, understanding the science of swimming and mastering how we apply information technology can aid u.s.a. poor land creatures to move as efficiently through the h2o as possible!

Question: Does swimming warm the pool?

If y'all're a fan of science, yous probably know virtually i of the greatest physics experiments of all time, which was carried out by James Prescott Joule in 1840. He was proving what's now chosen the law of conservation of energy—the basic idea that we tin't create or destroy energy, merely only convert information technology from 1 class to some other. He did information technology using this apparatus, in which a weight (1) running over a pulley (2) pulls on a rope (3) and spins a paddle bike then it agitates water inside a closed container (four), heating information technology upwardly by a modest corporeality. After repeating the experiment quite a few times to get a measurable temperature rise, Joule calculated that the potential energy lost by the falling weight was exactly the same as the oestrus energy gained by the h2o in the container.

Recently someone emailed me asking whether swimmers warm the water they're continuing or moving in, which is a more complex question than you might think for all sorts of reasons. Just it set me thinking about Joule's experiment and whether a puddle full of people, swimming furiously, would warm the water past a noticeable amount. This is the kind of "back-of-envelope" calculation that all physicists love!

Let'due south assume some things to make life piece of cake:

1. As people swim, all the energy their bodies produce in the process ends upward as heat in the h2o.
2. The only affair warming the water is the concrete agitation caused by the swimming. I'm going to completely ignore the ordinary heat lost from the swimmer's bodies to the cooler h2o (mostly past conduction).
3. All the free energy that goes into the water stays there. None goes into the air above or the material surrounding the pool.
4. The swimmers tin can happily keep pond away at a abiding rate indefinitely, no matter how hot the water gets (if indeed it does). At that place's no reason why the swimmers couldn't be replaced by other people and, if necessary, nosotros could put them in heatproof suits!
5. The specific rut chapters of h2o (the amount of energy it takes to heighten 1g of water by 1°C) stays the aforementioned every bit the temperature changes.
6. And then on. I'm only interested in a "guesstimate," not an exact calculation.

Allow'south assume that in that location are 50 swimmers in an Olympic size pool and they swim so fast that each of them consumes 1500 kJ of free energy per hour and puts that much estrus into the water. (That's a figure I've pulled from p26 of Richard Muller'southward first-class book Physics for Future Presidents, but information technology seems to be confirmed elsewhere. It's the equivalent of a few hundred calories.)

If 50 swimmers swim for 1 hour, we go a total heat energy input of 7.5 x 10viiJ.

How much does that warm the water? An Olympic-sized pool has a (fairly gigantic) volume of 2.5 million liters, and a liter weighs virtually a kilogram, so we have a mass of h2o of 2.5 ten ten6kg.

The specific heat capacity of h2o is well-nigh 4.2 joules per gram per °C (in other words, it takes 4.2 joules to enhance the temperature of i gram of h2o by 1°C).

So an free energy input of 7.5 10 x7J raises the puddle temperature past 7.5 x x7 / (4.2 × thou to catechumen kilograms to grams × 2.5 x x6) = 0.007°C!

If the h2o is 20°C to commencement with, how long would it take the swimmers to make it eddy?

We'd need a temperature rise of 80°C and nosotros know it takes an hour to give united states 0.007°C, then we'd demand our swimmers to keep going for eleven,200 hours = 466 days = about a yr and 3 months.

Respond

Does swimming warm the pool? 1. Yes—the energy swimmers generate has to go somewhere. ii. No—the heat they produce by swimming is so minute that information technology makes no difference any, and the rut lost from the h2o would more than brand up for it.

Discover out more

On this website

• Aerodynamics
• Energy
• Laws of motion
• Solids, liquids, and gases
• Surfing
• Scientific discipline of sport

Books for older readers

Science of swimming

• Swimming Science: Optimum Operation in the Water by Dr. John Yard. Mullen (ed). Ivy Printing/Quarto, 2018. An engaging, well-illustrated guide platonic for general adult readers who'd similar a little scientific insight.
• The Science of Sport: Swimming by past Alexander Marinof and Dr John Coumbe-Lilley. The Crowood Printing, 2017. This book puts the emphasis on getting your mind and body in elevation shape for swimming; there's less nearly physics, fluid dynamics, and those sorts of topics.
• Exercise Physiology: Nutrition, Free energy, and Human Performance past William McArdle et al. Lippincott Williams & Wilkins, 2015. The scientific discipline of swimming is discussed around p600 (including energy expenditure, drag, buoyancy, and the effect of water temperature).
• The Human Auto by R. McNeill Alexander. Columbia University Press, 1992. This book explains how the homo trunk works like a physical automobile, combining physiology with engineering concepts. Pond is covered on p112.

Swimming—general

• Swimming Anatomy: Your Illustrated Guide for Swimming Strength, Speed and Endurance past Ian McLeod. Human Kinetics, 2010. An illustrated guide to how man muscles work in swimming.
• Swimming Fastest: A Comprehensive Guide to the Science of Swimming past Ernest W. Maglischo. Homo Kinetics, 2003. Excellent, detailed, well-illustrated guide roofing all the different strokes.
• The Handbook of Swimming by David Wilkie and Kelvin Juba. Pelham, 1996. David Wilkie'southward books are older and harder to detect, but very clear guides that I find embrace the science of swimming very well.

Books for younger readers

• The Science Behind Swimming, Diving and Other Water Sports by Amanda Laser. Raintree/Capstan, 2016. A very basic 32-page introduction for ages viii–10.
• Swimming Science by Hélène Boudreau. Crabtree, 2009. A 32-page guide for ages eight–11.

Videos

There are lots of YouTube channels devoted to pond and triathlon; if y'all scout a few of them, y'all'll quickly realize how central science is to improving your swimming technique. Here's simply a tiny selection of freestyle (front-crawl) videos to starting time you off:

• Swimming Freestyle Smooth by Skills NT Pond.
• Three Front Crawl Technique Tips past Freestyle Optimizer.
• The Pull—How To Swim Front end Crawl by GTN.
• Easiest Way to Swim Freestyle by Phlex Swim.

References

1. ↑    "Chapter 10: Energy Expenditure During Walking, Jogging, Running, and Pond" in Exercise Physiology: Nutrition, Free energy, and Human Performance past William McArdle et al. Lippincott Williams & Wilkins, 2015, p601.
2. ↑    H2o - Dynamic and Kinematic Viscosity: Applied science Toolbox, 2020 [Accessed: May 25, 2020.]
3. ↑    Alexander quotes ~200 watts. The Human Machine by R. McNeill Alexander. Columbia Academy Printing, 1992, p.115.

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