The Physics of Water and Learning to Swim

Learning to swim and the physical properties of water rarely cross over, and I think that’s

a real shame. Water is truly an amazing substance that is the foundation of life as we

know it, but more importantly, we can swim in it.

The following ramble will shine a bit of light on the important features of water that can

make your swimming journey much easier and maybe make a bit of sense out of the

exercises and drills we get you to do here at CreateFit.

We’ll cover three main features:

- Density & Buoyancy

- Viscosity

- Turbulence & Efficiency

You may recognise terms but allow me to delve into why they’re vital to a much more

rounded understanding of how to swim.

Density & Buoyancy

We are around 70% water, but the rest of our body is made of lighter biological material

like fat, muscle, and air-filled spaces. This means water is slightly denser than us, which

is what allows us humans to float.

To have complete control over that floating, the lungs do most of that heavy work. Your

lungs work in much the same way a helium balloon works in air. Instead of a balloon full

of helium (which is lighter than air), it’s your lungs full of air, and instead of the

atmosphere, it’s the water supporting you.

The more air you hold in your lungs, the less dense your body becomes, increasing your

buoyancy and making it easier to stay high in the water. This matters because good

buoyancy helps keep your body horizontal, reducing drag and allowing you to swim

faster with less effort.

Next time you’re in the pool, try this: while floating, breathe slowly in and out, and notice

how your body rises and sinks with each breath. That simple change in lung volume is

one of the easiest ways to feel buoyancy in action.

Viscosity

Water is much thicker than air. In physics terms, it has a higher viscosity, meaning it

resists motion more strongly. This resistance is exactly what allows you to move forward

in the water.

When you swim, you are pushing against a dense, resisting fluid. Your hands and forearms act like paddles, pressing water backwards to generate forward motion

(Newton’s 3rd Law of Motion). If your hand slips through the water too easily, very little

force is transferred and propulsion is lost.

This is why we are often saying to “feel the water” or “hold the water.” A slow, controlled

catch allows you to apply pressure to the water, using its viscosity to your advantage. A

rushed stroke, on the other hand, causes the hand to slide through the water with

minimal resistance, wasting energy.

Viscosity also explains why technique matters more than raw strength. Two swimmers

with the same fitness can move at very different speeds depending on how effectively

they apply force to the water. Efficient swimmers maximise the surface area of the hand

and forearm and apply steady pressure throughout the stroke. Water’s resistance is not

your enemy. It is the medium that makes swimming possible.

Turbulence and Efficiency

When water flows smoothly around your body, it is relatively efficient. When that flow

becomes chaotic, swirling, and broken up, it becomes turbulent. Turbulence costs

energy.

Turbulence increases drag. Every overly splashy kick, wide arm movement, or poor body

position creates disturbed water behind you, forming a turbulent wake that slows you

down by pulling you backward. The harder you fight the water, the more resistance you

create.

Efficient swimming is therefore not about overpowering the water, but about moving

through it cleanly. A streamlined body position, smooth hand entry, and controlled kick

all help maintain more orderly flow around the body, reducing turbulence and

conserving your valuable energy.

This is especially important because drag increases rapidly with speed. As you try to

swim faster, turbulence grows disproportionately, meaning that small inefficiencies

become very costly to you. That’s why elite swimmers appear smooth and relaxed even

at high speeds. They are minimising wasted motion to the very best of their ability.

A useful mental shift is to think less about “making more power” and more about “losing

less energy.” Reducing turbulence doesn’t just make you faster; it makes swimming feel

easier and more sustainable. Efficiency in swimming is, at its core, the art of moving

water as little as possible while still moving yourself forward.

Swimming should be all about understanding the water. When you use buoyancy to stay

high, viscosity to generate propulsion, and efficiency to reduce turbulence, you stopwasting energy and start moving with the water instead of against it. Swim smarter, not

harder!

CreateFit Swim Coach: Sacha Mulcahy

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Flow and propulsion with Front Crawl