Whales and Larvae are Surprisingly Similar
You wouldn't think that a 100-foot-long, 170-ton blue whale would have anything in common with fish larvae, which measure millimeters in length. But researchers have shown that these two animals, and a host of others, are surprisingly similar.
A team from Harvard University has studied the science behind swimming, and using simple hydrodynamics, found that virtually every animal - from the tiniest fish larvae to the biggest creature on the planet - propel themselves the same way through water.
"What we wanted to investigate was how the speed of an organism changes as a function of how large it is, how quickly it moves and how much it moves," lead researcher L. Mahadevan said in a press release. "To resolve that in detail, however, is very complex, because there is a great deal of differences in morphology and what parts of the body different creatures use to swim. The question is: Is there anything in common across all these organisms? The answer, we found, is yes."
The findings were published in the journal Nature Physics.
Researchers began by delving into the physics of how different creatures swim.
"We instead thought that while swimmers exhibit a huge diversity in shapes and kinematics, at the end of the day they all live in the same media, water," explained co-author Mattia Gazzola.
Based on their mathematical model, the research team determined that the size of the organism, the amount it moves, and how quickly it moves all control how fast it moves.
But, this straightforward relationship, the researchers point out, is limited by a resistance factor, caused by skin friction, because water "sticks" to the organism's body. And the resistance changes as the marine animal moves at intermediate or fast speeds.
When all the compiled data - including 50 years of observations - were plotted on a graph, the researchers found that the swimming speed of virtually every organism, from fish larvae to frogs to birds, amphibians and even whales, could be described by one of the two equations.
"While it wasn't a surprise that the resistance changed at organisms moved faster, the fact that those challenges could be so simply described was interesting and provocative, because we are talking about organisms that range in size from a few millimeters to the size of a blue whale," Mahadevan said.