Wednesday, 1 August 2012

Why Micheal Phelp's Shaves Himself and Surface Tension in the Olympics

Water sticking to the surface of skin

I love swimming.  I have been swimming well since I was young.  Although I never really participated in any races I would consider myself a decent swimmer.  I was watching the Olympic swimming and was looking at how these swimmers break the surface of the water.  There are several forces at play that can make a break a swimmer.  These forces are the resitant (surface area contact with water) and propellant forces.  With underwater cameras and understanding these physical principles it is possible to make swimmers faster.

Frontal resistance - the greatest ally or downfall of a swimmer caused when the body rides too low in the water.  To elliviate this swimmers roller the body in the water to reduce the surface area of their body on the water.

Skin Friction- is the area where the water is in full contact with the skin to travel at 0 m/s^2.  One easy way is to do what most swimmers do is to shave themselves and use body lotion.  Micheal Phelps and the rest of the Olympians probably do   This can decrease the time by about 1 second for every length of the pool.  A second way used biomimetics from understanding the surface tension of fish.  This is mentioned later.

Eddy Resistance - is caused by poor swimming technique and riding low in the water so small vortexes are still bound to the swimmer after each stroke.  The swimmer will want to get rid of these small eddy currents to propel the forward faster.

Lift - the most important to swimming shows that the Bernoulli principle affects swimming stating that the speed of the fluid particle increases as it travels through a horizontal streamline.  The S shaped pattern when the swimmers arm passes over the bodies axis of rotation produces lift like a propeller.

If one were to think that the swimmers technique is fully optimized frontal resistance, eddy currents and lift should be optimized as well.  The one physical factor that is more difficult to change would be the surface area contact with the water and the breaking of the surface tension.  Can swimmers swim better underwater if  they have the ability to change the surface tension on their skin and suits?

Some swimmers discovered that they could kick underwater faster than they could swim on the surface. Those who were great kickers would kick almost the entire length underwater and then surface right before the turn, do a stroke and a turn and go as far as they could underwater on the next length.

The result of this was that the International Swimming community decided that swimmers were supposed to swim, not just kick and now, at all levels of swimming, there is a 15 meter rule. That rule came into existence about 10 or 12 years ago and it requires a swimmer to be on the surface by the time they reach 15 meters from the start or a turn. If you go past 15 meters underwater you are disqualified (DQ). You'll notice that most lane lines have one red marker about 9 yards from the wall ... that is the same as 15 m from the other wall.

So breaking the water surface reduces the speed in swimming.   The surface tension will make a difference of a few tenths of a second which is about the time that is needed to win or lose a competition.  This is a difference between gold, silver, bronze and invisibility in swimming.  So controlling surface tension is important.  Could a swimmer cover themselves in soap to reduce the surface tension?

 A second way that is even more popular today with rocktape and new materials is to use compression suits with seamless fabrics and using a fish skin riblet.  The compression suits reduce muscle wobble.  The fish skin riblet designed by Speedo made with repetitive grooves of tens of millimeters to one millimeter grooves which can reduce the friction resistance of a fluid.  In fact films of this kind are made by 3M and are used in yachting to reduce biofouling.  Possibly, a surfactant or biofoam could be applied on the front side of a swimmers body to reduce the surface contact.

Swimming pools have dividers in the lanes that have a disc that rotate when hit by a wave to dissipate the surface tension waves in a competitive pool