Wednesday, 2 March 2011

I hate belly flops

Watching this video makes me cringe!!

Everybody has probably belly flopped at some point so they are probably doing the same face as I am right now. But after watching this video I am wondering why the water was such a hard landing.

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.

If the guy in the video were a better diver like lets say David Hasselhoff in Baywatch then perhaps it would have looked better. So the next time you dive in water you put your hands in front to break the water, 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).