Press Trust of India
New Delhi, December 1
Does the claim of walking on water by some Indian yogis have a scientific basis?
A definite answer to this is yet to come but the US biologists S Tonia Hsieh and George V Lauder at Harvard University have explained how some lizards are able to run on water at speeds of about four kilometres per hour or more.
Basilisk lizards (Basiliscus plumifrons) are proficient water runners, regularly dashing across bodies of water to evade predators. The Harvard scientists have made direct measurements of the force produced by the lizards while running across water using "digital particle image velocimetry."
The technique involves seeding the water with reflective particles and illuminating the area of interest with a thin laser sheet. Particle movement can then be traced and the forces calculated.
Waterfowl are known to slap the water with their feet during flapping take-off. However, they obtain a great deal of lift from their wings. Basilisk lizards that weigh up to 200 grams are unique in that they regularly run across water, using only their feet as a source of both lift and thrust.
In their study, five juvenile basilisks were induced to run across a 0.8-m-long water track. Each running sequence was filmed with two synchronised high-speed cameras.
They found that the lizards produced greatest support and propulsive forces during the first half of the step, when the foot moves primarily vertically downwards into the water. They also produced large transverse reaction forces that change from medial to lateral throughout the step.
"These forces may act to dynamically stabilise the lizards during water running," the scientists reported in the Proceedings of National Academy of Sciences.
"This study quantifies the forces produced after the foot impacts the water to understand how basilisks are able to produce both propulsive thrust and lift during bipedal locomotion on water," they said.
"Our results give insight into the mechanics of how basilisk lizards run across water," they said and added "basilisk lizards, therefore, serve as interesting model organisms for examining the mechanics of this remarkable locomotor feat".
http://www.hindustantimes.com/news/1...8,00040010.htm
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