The Physics of Water and Learning to Swim
- Feb 2
- 3 min read
Updated: Mar 17
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 stop wasting energy and start moving with the water instead of against it. Swim smarter, not harder!
CreateFit Swim Coach: Sacha Mulcahy
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