As energy is alternately stored and released on both sides of the animal’s body, the tail whips strongly back and forth. This whip-like action propels the animal through the water like a living bullet。
Source of Energy
What causes the fibers to store so much energy? In finding the answer the Duke University scientists learned that the shark’s similarity to a belted radial tire doesn’t stop with the skin. Just as a radial tire is inflated by pressure, so, too, is the area just under the shark’s collagen “radials”. Instead of air pressure, however, the pressure in the shark may be due to the force of the blood pressing on the collagen fibers。
When the shark swims slowly, the pressure on the fibers is relatively low. The fibers are more relaxed, and the shark is able to bend its body at sharp angles. The animal swims this way when looking around for food or just swimming. However, when the shark detects an important food source, some fantastic involuntary changes take place。
The pressure inside the animal may increase by 10 times. This pressure change greatly stretches the fibers, enabling much energy to be stored。
This energy is then transferred to the tail, and the shark is off. The rest of the story is predictable。
Dolphin Has Speed Record
Another fast marine animal is the dolphin. This seagoing mammal has been clocked at speeds of 32 kilometers (20 miles) an hour. Biologists studying the dolphin have discovered that, like the shark, the animal’s efficient locomotion can be traced to its skin. A dolphin’s skin is made up in such a way that it offers very little resistance to the water flowing over it. Normally when a fish or other object moves slowly through the water, the water flows smoothly past the body. This smooth flow is known as laminar flow. However, at faster speeds the water becomes more turbulent along the moving fish. This turbulence muses friction and slows the fish down。
In a dolphin the skin is so flexible that it bends and yields to the waviness of the water。
The waves, in effect, become tucked into the skin’s folds. This allows the rest of the water to move smoothly by in a laminar flow. Where other animals would be slowed by turbulent water at rapid speeds, the dolphin can race through the water at record breaking speeds。
Other Animals Less Efficient
Not all animals move as efficiently as sharks and dolphins. Perhaps the greatest loser in locomotion efficiency is the slug. The slug, which looks like a snail without a shell, lays down a slimy trail over which it crawls. It uses so much energy producing the slimy mucus and crawling over it that a mouse traveling the same distance uses only one twelfth as much energy。
Scientists say that because of the slug’s inefficient use of energy, its lifestyle must be restricted. That is, the animals are forced to confine themselves to small areas for obtaining food and finding proper living conditions. Have humans ever been faced with this kind of problem?
1.According to the passage, a shark can use movement to do something except______________。
［A］to find food
［B］to avoid being chased by its enemies
［C］to find a new place to live
［D］to show its braveness
2.Examples of automobiles, rockets and submarines are used to show that _______________。
［A］humans are the most clever living creatures in the world
［B］human inventions enable us to travel in almost any kind of environment
［C］humans are very successful in inventing transportation tools
［D］humans can’t move like other animals in any circumstances
3.What is the key to the shark’s swift locomotion in water?
［A］The skin.［B］The tail.［C］The muscle.［D］The jaw。
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