definition

With physical laws, an attempt is made to further improve and optimize the individual swimming styles. These include static buoyancy, hydrodynamic buoyancy and the various opportunities to move in the water. It uses biomechanical principles and physics.

static buoyancy

Almost every person manages to float on the water surface without buoyancy aid. This apparent weight loss is due to static buoyancy.

For example, a body dips into the water, it displaces a certain body of water. It acts on this body, a buoyancy (static buoyancy).

  • The static buoyancy corresponds to the weight that displaces the body of water mass
  • The static lift is opposite to the weight. (upward)

For example, in the water it is possible to easily lift a squat float through a much weaker person. If you now lift body part of the carried out of the water, the static buoyancy decreases, and the lifting is difficult.

Deep breathing increases the lung volume and thus the total body volume, increasing the static buoyancy.

Ex. A floating float exhales and sinks to ground.

The decisive factor for the buoyancy of the body in the water is therefore the specific gravity (density of the body). The greater the density of the body, the more the body sinks in the water. Athletes with heavy bones and many muscles have a greater density and sink much more, and thus have disadvantages when swimming. Women have more subcutaneous fatty tissue compared to men, and thus have greater static buoyancy and better water management.

static buoyancy and water position

The water situation is crucial for fast and long swimming. 2 physical points of attack are important for the correct position of the water. On the one hand the body center of gravity (KSP) and the volume center (VMP). The human KSP is located approximately at the navel level and is the point of application for the downward force of gravity. The VMP is the point of attack for static buoyancy and due to the voluminous rib cage it is approximately at chest level. In the water KSP and VMP shift over each other. Ex. A cuboid (half Styrofoam, half iron) is not on the water surface, but the metal half sinks, and the cuboid is vertical, with the Styrofoam side up.

Similar to the cuboid, this principle works with the human body. KSP and VMP approach each other and as a result the legs sink and the body is increasingly vertical in the water.

Important! Legs that are too low in the water do not generate propulsion and increase water resistance, ie legs to the surface.

In order to avoid the sinking of the legs, it is advisable to work with a diaphragm / abdominal breathing instead of chest breathing, so that the VMP is kept as close to the KSP as possible, and leave the head in the water and stretch the arms far forward. This results in a shift of the KSP headwards towards VMP.

Laws for bodies floating in the water

A body moving in water has various complex effects that need to be explained to understand how to swim.

Forces created in the water are differentiated in braking and driving.

The total resistance, which counteracts the human body in the water, consists of three forms:

The frictional resistance arises from the fact that individual water particles are pulled along the skin of the swimmer a certain amount ( boundary layer flow ). With increasing distance from the float this so-called static friction decreases. Dependent on this friction resistance of the surface structure, which is why in recent years in swimming swims increasingly with low-friction swimsuits.

The most important resistance to swimming is form resistance. Here, water particles are moved against the movement / swimming direction and act on the float braking. The shape resistance depends on the body shape and the water turbulence in the wake. See body shapes and flow.

As a last resistance, swimming causes a so-called characteristic impedance. Simply put, this means that by swimming and sliding, water must be raised against gravity. Waves arise. This resistance is dependent on the water depth, which more and more swimmers take advantage of and complete the gliding phases in much deeper water.

Hydrodynamic lift

The hydrodynamic lift is clearly visible on the wing of an aircraft. The wing surface of an aircraft is designed so that the air flows around different lengths paths on the wing sides. Since the air particles come together again behind the wing, the wing sides have to flow around at different speeds. And that: faster above and slower down. This creates a dynamic pressure below the wing and a suction pressure above the wing. So the sequence takes off.

The same but not so perfect happens with the float in the water.

This buoyancy is illustrated by the following example. If you lie down flat in water your legs sink relatively quickly. But if you are constantly pulled by a partner through water, the hydrodynamic lift causes the legs to be held on the water surface.

The direction of action in swimming is divided as follows:

Resistance : Against the swimming direction

Hydrodynamic lift : Perpendicular to the direction of swimming

Drive: In the direction of swimming

Body shapes and flow

Not the frontal area of ​​a body, as assumed earlier, but the ratio of frontal area to body length plays the most important role in the resistance in the water.

This can be illustrated by the following example.

If you draw a plate and a cylinder mitgleicher face by water, although the water resistance in front of the body is the same size, the turbulence in the wake are significantly different.

The term forehead resistance is therefore not entirely correct, since the turbulence in the wake slows down the body more.

According to recent findings, the spindle-shaped structures of the penguins have the least turbulence in the wake. Fish with these body shapes are among the fastest swimmers.

An example of the backflow:

A person walking through the water pulls a partner who is perched on the surface of the water by the resulting suction effect behind him.

Drive in the water

Propulsion in the water can be done by changing the shape of the body (fins movement in fish) or by drive-generating structures (propeller). In both methods, water is set in motion and thus acts on the floating body. The mutual reaction is called abutment.

In the following, the three principles for locomotion in water are explained in more detail.

1. Pressure paddle principle:
Eg duck feet : Here the feet of ducks are moved perpendicular to the direction of movement (backwards). At the back creates a negative pressure (dead water), which slows down the floating body. A lot of energy is necessary and the propulsion is low.

2. Reflection principle:

Eg Squid : The squid collects water in its body and ejects it through a narrow channel. This causes a drive on the body

3rd undulation principle:

Eg Dolphin : behind each body, rotating water masses appear in the wake. However, these rotating masses of water are in most cases disordered and have a braking effect. In Delphin, the masses of water are arranged by a body wave and thus can be useful for propulsion. These ordered masses of water are called vortexes. In swimming, however, it is very difficult by a body movement to move the water masses into an orderly rotation. In the power range, however, it allows very high swimming speeds.

drive concepts

Conventional drive concept:

In the conventional drive concept, the body parts used for the drive are moved in a straight line and opposite to the direction of swimming (actio = reactio). Here, large volumes of water with increasing speed but little propulsion are moved (paddle steamer).

Classic drive concept:

Drive by means of hydrodynamic buoyancy (comparison to the ship's propeller).

However, this drive concept is controversial, since the propeller is always flown from the same side with water and the palms do not swim. In addition, this drive works only after a certain run length, the arm pull while swimming is only 0.6- 0.8 m.

Vortex drive concept: (currently used model)

The rotating masses of water in the wake of the feet and hands have become increasingly important in recent years as an abutment producer.

A vortex arises when masses of water move from the traffic jam to the suction area. It tries to accommodate a lot of body of water in a small space, comparatively with the curling up of a carpet. The vortex occurs behind the feet as a roll form, and behind the hands as a pigtail shape.


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