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Putting physics to work in swimming


In our Swim Faster Madison program, I’ve discussed some of the physical forces that we work with to swim faster, especially buoyancy and gravity, and drag and propulsion. Now I’m going to talk about two more principles that govern the point where each arm enters the water and why it is important to “anchor” the catch.


The Law of Conservation of Energy (still with me?) looks at what happens when potential energy transforms into kinetic energy. Imagine a ball in a vacuum chamber held up in some way. We know that gravity would drop the ball to the bottom of the chamber when the ball is released. So the ball sitting above has potential energy, and the dropped ball has kinetic energy (until it stops). The equation for this effect is that the change in potential energy plus the change in kinetic energy is zero—they balance each other out.


Now let’s fill that chamber air. First, the ball will not drop as quickly as in a vacuum because the molecules in air dissipate some of the kinetic energy. Now the equation above is unequal, and the difference represents the work done by the dissipative forces of the air. This is the drag force that the air creates. Fill the chamber with water, and the ball drops even slower and the difference between potential energy and kinetic energy increases again.


In physics, the term conservation means something that doesn’t change. It is conserved. The Law of Conservation of Energy states that the total energy of an isolated system remains constant; it is said to be conserved over time. It means that energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another. So where does that energy go in a chamber filled with air or water? It becomes thermal energy (heat) from the friction caused by the dissipating force.


Okay, so what does this have to do with swimming faster, anyway? Well, everything actually. When we talk about an “isolated system” it means that gravitational force or the density of water don’t change. We work on streamlining from a wall and observing how the drag force of water slows the body to a stop. At the starting point, potential energy is in the muscles that will drive you forward, and kinetic energy is your movement through the water. Eventually you stop as all of the energy is dissipated by the water. The energy is converted into heat. You may not feel it, but it’s there. Push off fast enough and you could (theoretically) boil water.


An ideal swim stroke minimizes drag and maximizes propulsion. Factors that affect drag are a body position that isn’t horizontal, arms that cross in front of the head, or hips the swing left and right rather than around the axis at the center of your body. At Swim Faster, we do a lot of work to maintain a streamline form and rotation. The better you get at this, the faster you swim. We also work on the propulsive force of the stroke itself. I ask swimmers to imagine parallel tracks in the water. All of your propulsive force should be along those tracks. Any deviation from those lines is wasted energy.


Getting back to our Law of Conservation of Energy, the stroke is kinetic energy, and the goal is to reduce as much as you can the differential between the potential energy from your body and the kinetic energy of your stroke. Please take note that even the fastest swimmers work at this goal all the time.

Studies of swimmers have shown that a “front quadrant” stroke is more effective than when each hand is opposite the other in a windmill fashion—and here I’m talking about distance swimming where “conservation of energy” means being able to maintain a swimming pace for several minutes, or even hours. (Sprinters can windmill because all of their energy comes from an anaerobic system and the goal is to move the arms through the water as fast as possible.)


A “front quadrant” stroke means that one hand is always in front of the shoulders. Watch a proficient swimmer, particularly in the middle distances, and you see that they extend the arm starting the catch while the opposite arm recovers. I call this anchoring the catch. Note that there isn’t a glide in the stroke. While extending the arm, the swimmer rotates to start the pull, and the hand, arm and body are always active. No glide, just full extension. It is the the critical moment where your transfer of potential energy to kinetic energy is most efficient.


This brings up another topic of physics, the Bernoulli Principle. In fluid dynamics, an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy. This is the principle behind an airfoil, where the pressure above the curved top of a wing is less than the pressure below, causing the wing to lift.


When a swimmer drives the hand into the water with fingertips first, then wrist, then elbow, and extends, the arm and hand act as an airfoil, creating (beneficial) lift in the stroke. This creates the moment in the stroke where you can smooth out your body hand to hips while you travel forward. If you hold the hand out in a glide, your movement (kinetic energy) starts to slow. The goal is to establish a good catch as the opposite hand recovers and then start to pull with maximum propulsion.


One of the sets I use in my program is to start a lap in a full catch-up stroke. Transition to a three-quarter catch-up and into then a normal stroke. Repeat this exercise to help you find the optimal timing of recover-catch-pull in your freestyle stroke, optimizing the conservation of energy and exploiting the Bernoulli Principle. I encourage all swimmers to build this set into their warm-up and drill routines to help develop the ideal timing in their freestyle.

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