Водні гідродинаміка плавання: опір, воронковий рух та техніка

Hydrodynamic Forces in Swimming

The total resistance experienced by a swimmer is composed of three distinct components: skin friction, form drag, and wave drag. Skin friction arises from the viscous shear within the boundary layer surrounding the swimmer’s body.

Form drag develops due to the separation of the flow behind the swimmer's body, creating a pressure differential that opposes motion. This effect is influenced by the shape and orientation of the swimmer.

Wave drag results from the energy expended in generating bow and stern waves as the swimmer moves through the water. The magnitude of wave drag increases significantly with speed.

F_friction = ½·ρ·C_f·S_wet·v²        F_form = ½·ρ·C_d·A_frontal·v²
Elite whole-stroke mechanical efficiency: only 5–9%
(runner/cyclist: roughly 20–25%)

Thrust comes from shed vortices, not a flat push

Early "paddle theory" assumed a hand pushes straight backward against still water. Modern particle-image-velocimetry studies show the real mechanism is closer to how a fin or a small wing works: the hand follows a curved, S-shaped sculling path that continuously changes its angle of attack, generating thrust from a combination of lift and drag rather than a single backward shove. This is why elite freestyle and butterfly pulls trace a visible hourglass pattern through the water rather than a straight line.

Why body position matters more than raw power

Human body density sits close to water's, so a full inhale noticeably increases buoyancy versus a full exhale — but the centre of buoyancy (near the air-filled chest) sits above and forward of the centre of mass (near the denser hips), so the legs tend to sink unless corrected by head-down alignment and a stabilising kick.

If the hips sag even 5-10° below horizontal, frontal area — and therefore form drag, which scales with velocity squared — can increase by 50% or more, a far bigger performance cost than most stroke-timing errors.

Frequently asked questions

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