Laws for bodies gliding in water

A body moving in water produces various complicated effects that need to be explained to understand swimming. Forces arising in water are divided into braking and driving forces. The total resistance, which counteracts the human body in the water, consists of three forms: The frictional resistance is caused by the fact that individual water particles are pulled along a certain distance by the skin of the swimmer (boundary layer flow).

With increasing distance from the float, this so-called static friction decreases. This frictional resistance depends on the surface structure, which is why swimmers have increasingly been using low-friction swimming suits in recent years. The most important resistance for swimming is the form resistance.

Here, water particles are moved against the direction of motion/swimming and have a braking effect on the swimmer. The form resistance depends on the body shape and the water turbulence in the wake. See body shapes and flow.

The last resistance that occurs during swimming is the so-called wave resistance. Simply explained, this means that by swimming and gliding, water must be lifted against gravity. Waves are created.This resistance depends on the depth of the water, which is something that more and more swimmers are taking advantage of and completing the glide phases in much deeper water.

Hydrodynamic lift

The hydrodynamic lift is clearly visible on the wing of an airplane. The wing structure of an aircraft is designed in such a way that the air flowing around it travels different distances on the sides of the wing. Since the air particles come together again behind the wing, the air must flow around the wing sides at different speeds.

This means: faster at the top and slower at the bottom. This creates a dynamic pressure below the wing and a suction pressure above the wing. So consequence the airplane takes off.

The same thing, but not in such a perfect way, happens with the float in the water. This lift is illustrated by the following example. If you lie down flat in water, your legs sink down relatively quickly. However, if you are constantly pulled through the water by a partner, the hydrodynamic buoyancy causes the legs to be held at the water surface. The direction of action in swimming is divided as follows: Resistance: Against the swimming direction Hydrodynamic buoyancy: Perpendicular to the swimming direction Drive: In swimming direction