What Is Gray's Paradox And What Do Dolphins Have To Do With It?

By Antonia Čirjak on May 4 2020 in Questions & Answers

The idea behind this paradox was to try and determine how dolphins can achieve such extremely high speeds and accelerations while swimming, given how small their muscle mass is.
The idea behind this paradox was to try and determine how dolphins can achieve such extremely high speeds and accelerations while swimming, given how small their muscle mass is.
  • Gray’s paradox originates from the famous British zoologist James Gray who stated that dolphins should not be able to swim as fast as they do give their muscle strength.
  • This paradox was proven to be wrong by other scientists in 2008, by researching dolphins in greater detail.
  • It was discovered that dolphins could actually exert much more force than it was originally believed.

Gray’s paradox is a well-known paradox that dates all the way back from 1936. It was first stated by the esteemed British zoologist Sir James Gray. The idea behind this paradox was to try and determine how dolphins can achieve such extremely high speeds and accelerations while swimming, given how small their muscle mass is.

Gray tried to estimate how much power a dolphin could utilize based on its anatomy, and he concluded that this power should not be enough to go against all of the forces in water. This is why it is called a paradox because the dolphins manage to achieve something they should not be able to. Gray assumed that the skin of a dolphin contains some properties that allow it to go against the drag forces in water.

The Paradox Is Wrong

It needs to be noted that Gray’s paradox is not correct. Scientists from West Chester University, Rensselaer Polytechnic Institute, and the University of California in Santa Cruz managed to prove Gray wrong in 2008. They used a method called digital particle image velocimetry to do so. They videotaped dolphins while they were swimming through water that was filled with a large number of small air bubbles.

The names of these dolphins were Primo and Puka. By using special computer software and measurement tools made for aerospace, they managed to analyze the particle-image velocimetry captured at 1,000 frames per second, which is an extremely high frame rate.

Gray assumed that the skin of a dolphin contains some properties that allow it to go against the drag forces in water.
Gray assumed that the skin of a dolphin contains some properties that allow it to go against the drag forces in water.

Using this method, they were able to measure the exact force a dolphin can utilize. The results were astounding, to say the least. It was discovered that a dolphin could utilize almost 200 lb of force whenever it thrusts its tail. This force is actually ten times larger than what James Gray believed, so his hypothesis was proven to be wrong. Not only that, but it was also discovered that at peak force, dolphins could utilize anywhere between 300 and 400 ln of force.

Other Important Research

More research was done on the dolphins while they were doing tail-stands. A tail-stand is a trick that dolphins often do when they create an illusion of walking on water. They do this by holding the majority of their bodies above water while strongly moving their tail underwater to support themselves. 

There was other research done that is tied to Gray’s paradox. For example, researchers from Taiwan did research on the swordfish. They tried explaining the swimming capacities of the swordfish, so they developed the concepts of “circulating horsepower” and “kidnapped airfoils.” This is important because the swordfish can swim at even higher speeds than dolphins. This is another way of disproving Gray’s paradox.

While Gray’s approach was not completely wrong, seeing as how he assumed that the forces of drag and thrust are equal in force but move in opposite directions, he did not include some important facts. It is necessary to mention that a swimmer does not need to actually use energy to overpower the drag forces in the water using only their muscles. The thrust forces help them during this task. Since higher drag forces also create a higher trust force, no energy principles were violated, which means that Gray’s paradox actually does not exist.

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