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Swimmer at rest (not in motion) ->
In order for an object to float in water, the object must be less dense than the water. The floating happens by the buoyancy force that is acted upon by the water. This is based on Archimedes' principle, that any object that is suspended in a fluid is acted upon by an upward buoyant force equal to the weight of the fluid that is displaced by the object.
The weight of the object is equal to the buoyant force being acted upon the object.
The buoyant force acts through the center of buoyancy, which is the center of the immersed part of the object, which is the volume displaced by the object.
To maintain the object's orientation in the water, this buoyant force must pass through the center of mass of the object.
An object floating in water will eventually reach translational equilibrium.
<- Swimmer in motion
By moving her arms through the water, she creates a thrust force that propels her forward. When she is moving at a constant speed, the thrust force is equal to the drag force, which is created by her motion through the water.
For the freestyle stroke, the thrust force is primarily created by the swimmer's arms, whereas the feet mostly help maintain the streamline position, which helps reduce drag.
Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. This is often seen on camera when Olympic swimmers are about to break the surface of the water, which looks as if they are perfectly wrapped in glass.
Swimmer During a Flip Turn ->
If we snapshotted the forces acting upon a swimmer during their flip-turn, specifically when the swimmer is about to push off of the wall (there is a slight pause where the swimmer is stationary, but for a very short time), the forces would be as follows:
According to Newton's Third Law, every action has an equal and opposite reaction. Therefore the force in newtons acting upon the swimmer's feet by the wall is the same as the force in newtons of the swimmer's feet acting on the wall.
The buoyancy forces and weight forces still apply to the swimmer when she's on the wall. Therefore, these two forces would be equal.
When the swimmer pushes off the wall, however, the drag force applied on the swimmer by the water increases, so the swimmer would not be in equilibrium. Though the swimmer is accelerating forward, the drag force of the water prevents the swimmer from accelerating further.
The Effect of Limb Position on Drag
The Effect of Limb Position on Drag
Breastroke
Historically, breastroke is the slowest swimming stroke in terms of speed.
This is because during leg recovery, the thighs are pulled forward into the water against the swimming direction, which creates drag.
The way you "shoot" your arms out in front of you affects your propulsion
Backstroke
One of the main contributors of drag in the water is not maintaining a streamlined (straight) body position in the water.
This streamlined position is especially important in backstroke as kicking from the hips allows the swimmer to keep the legs straight, whereas kicking from the knees causes the calves to drop, breaking the streamlined position.
Using the knees instead of using the full leg by incorporating the hips hence causes drag.
One crucial part to swimming backstroke is keeping your head aligned while rotating your whole body.
Butterfly
The hardest stroke, Butterfly, is considered the most difficult because of the precision of the technique required.
Having a strong core is essential since you use it to lift yourself up a bit.
Having a strong "down" kick will help you propel through the water as well as putting your head down before your arms come around.
Propulsion Forces - Why these forces matter
In order to even create propulsion, your hand or foot must be pushing the water backwards.
Using your whole entire arm or leg creates way more propulsion than just using one part of it. It's all about the surface area.
The duration of a stroke matters as well. For example, in butterfly, when finishing your stroke, be sure to finish with both arms parallel to each other in front of your head rather than spread apart.
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