Water carries our bodies
2.0 Why does our body float ?
Contrary to popular thinking, the human body does not sink. It floats, more or less depending on the person. But if you immerse yourself completely in the water without any strong support, whatever your position, you will notice that you are attracted by the surface and not by the bottom.
Here's a simple example :
Do air bubbles in water rise to the surface or sink? Now let's take the human body, what is in our lungs?
We can therefore conclude that the more air we fill our lungs with, the more we float. Before you can «sink» , you need to empty your lungs completely (which is not so easy). It's up to you! Give it a try!
2.1 Archimedean buoyant force
Here's a more scientific explanation of why we float in water.
Archimedes' buoyancy is the force applied to our body in water. It is a vertical force, from bottom to top. It applies to the centre of buoyancy (the geometric centre of the volume underwater, in this case our body). For us in the horizontal position, this centre is located at the level of our navel (it can be represented by a point).
Archimedes' buoyancy allows our body to rise to the surface after a jump, for example, or a voluntary descent underwater. Its intensity is equal to the weight of the volume of fluid moved. AP = mass of water x g.
To illustrate, if you breathe out in water, the rib cage deflates and the volume of the body (underwater) decreases, so the intensity of the buoyancy force decreases. If the buoyancy is less than the weight, the body sinks.
Buoyancy DOES NOT depend on the shape of the body or the amount of surface area of the body on the surface of the water.
2.2 Hydrodynamics or the projectile body
Water is a fluid with density. When we move, the shape of our body acts as a brake. Water is a resistant environment whose characteristics cannot be changed. So we can change our own characteristics to move with less effort.
Our body, like a boat, has to find the most hydrodynamic position to move with minimum braking and maximum efficiency.
The most hydrodynamic position for us is: the neck in extension (chin towards the chest), the arms in search of maximum extension (arms stretched behind the ears, hands one on top of the other in the flow), the legs closed, in extension up to the toes.
Of course, when we swim, our body deforms, and the hydrodynamic position can't be as optimal as if we weren't moving. But you have to keep this position in mind, and try as far as possible not to move too far away from it. The further you move from this position, the more your body becomes a brake on movement.
For example, if your neck is not extended and you look forward when you swim, even if your head is underwater, this is already a hindrance. Let's exaggerate the position. Have you ever tried to swim a front crawl with your head still above the water? Keeping the full stroke. Try it and you'll see that it's much more tiring because in this position your legs sink, unless you have a very good stroke, and your body comes to stand perpendicular to your direction of movement.
Again with the aim of being as hydrodynamic as possible, an aerial return of the arms is used in the various swims. This is simply because air is 800 times less dense than water. This means there is much less resistance in the air, allowing the arm to return quickly.
2.3 The swimming theorist
Raymond CATTEAU revolutionised the teaching of swimming. Before him, there was a certain way of teaching, which is totally different today. His method, which is based on logic, has won unanimous acclaim for being so easy to understand and apply. He is mentioned in all training courses, whether by the FFN (French Swimming Federation) for the BPJEPS (Professional Diploma in Youth, Popular Education and Sport) or the DEJEPS (State Diploma in Youth, Popular Education and Sport), or in STAPS (Sciences and Techniques of Physical and Sports Activities) specialising in swimming. More than just a reference, it is the benchmark that is quoted today when talking about teaching swimming.
In his book, La Natation de Demain, the aim is to bring swimmers and coaches back to the basics of movement in the water. In other words, mainly posture and motor coordination. The coach's job is not to correct the swimmer from an external point of view, but rather from the swimmer's internal point of view (his sensations). In addition, the swimmer becomes involved in his or her training, because with this method the swimmer is asked to think rather than just apply. The aim is to make the swimmer aware of the impact of each of their actions on their stroke. They must therefore think about what they are doing at any given moment. It's up to the coach to pass on his knowledge, in an educational and non-directive way. For example, if a swimmer raises his head too much, he's no longer correctly aligned and doesn't go through the water as well. These effects are reinforced at high speeds. So rather than telling the swimmer to pull his head in, we're going to get him to think about how he positions himself in the water and what the best solution is. If he's not convinced, the coach will set up contrasting tasks to prove to the swimmer what he wants him to understand. In fact, we no longer describe a movement to the swimmer, we ask him to feel its effects. This is a cognitivist learning model based on muscle control.
