Wednesday, 1 August 2012

'Don't be Splashy' Olympic Syncronized Diving

I was watching Olympic synchronized diving and was cheering on the Canadians.  The men's and women's teams both won metals.  It was my first time waching this competition and was suprised that they really judge splashiness.  One way to stop splashiness is to change the posture of the divers by using rocktape to help them streamline into the water.  What causes the splashyness?

The antithesis to divers are bellyfloppers.  Everybody has probably belly flopped at some point (not everybody is an Olympic diver).  So what is belly flopping and how does water's properties play into making splashes?

Two factors play here: the compressive strength and the shear strength. The compressive strength (and oppositely the tensile strength which is related to the surface tension) of a material like water depends on the molecules. The shape of water molecules determines how they line up (or don’t line up) when under pressure and compressed to move closer together. Atoms in a body of water will try to find an equilibrium position and distance themselves throughout the material (in this case the ocean) to return to equilibrium. The compression strength is what makes the belly flop hurt and makes me cringe. Compressive strength is measured in dynes/cm2.

The shear strength is like the shearing force or rigidity. Shear strength is measured in dynes/cm2. Water has zero rigidity. Like if you were to turning a round jar of water with a fish in it--the jar turns but the water does not, and the fish is still facing the same direction. This is because the sides of the jar slide across the water without affecting it--water has no shear strength. Put gelatin in the jar and you have a material with shear strength--and the fish will turn with the jar (do not try this at home). In the case of the belly flopper, since he jumped with his whole body parallel to the plane of the water he confronted the in-compressibility of water mentioned above.

However, during training the Canadians and other divers are likely to suffer severe injuries if they attempt a new dive and spin out of control.  One example is the German diver Stephan Feck who during his 3 meter spring board dive hit the surface of the water with his back after failing a pike.  See horrific video here.

What the Feck?

At several points during the evolution of the sport people created better tools to make the once named fancy diving safer and more fun.  A tool called the bubble machine invented by Herb Flewwellyn (a Canadian) in the late 1960's makes diving a little safer.  It works by creating a mass of bubbles in the center of the diving well.  The bubbles break the surface tension of water to create a "softer landing zone" .  The compressibility of the water would still be a factor but the initial hitting of the water may relieve some of the energy needed to break the water.

So the next time you dive in water you put your hands in front to break the water as the Olympic swimmers do, and, if you do it right, you slide right into the water without pain--again because water has no shear strength. You also displace as little water as possible making less of a splash. Diving like this would make me cringe less.

(Some info was found here in this great explanation of seismic waves).