2010年3月12日托福机经英文版原文(康老师)

　　2010.3.12北美

　　2. 人的行走和鱼游鸟飞相比，那种更耗energy，结论是是人类走路最耗能量。

　　Locomotion: Energy Cost of Swimming, Flying, and Running

　　The energy expended by animals as they swim through water, run on land, and fly in the air in the different kinds of locomotion is not immediately obvious to us. We know that a flying bird must continuously expend energy to keep from falling to the ground, and that in water many animals are neutrally buoyant and expend little effort to keep from sinking, but man has no experience in flying under his own power and he is a clumsy and ineffective swimmer. Walking and running we know more about, for man is our best and most cooperative experimental animal. Except for man and dog running animals have not received much attention, and studies of swimming and flying animals have only recently been carried out at a satisfactory level of success. In this article I shall compare the energy cost of these three kinds of locomotion.

　　Other types of locomotion exist, such as the hydraulic system of the earthworm, in which the body fluids in combination with the muscular body wall function as a "skeleton." Spiders lack extensor muscles in the limbs and use blood pressure to stretch their legs; the squid and octopus use jet propulsion in swimming. The mechanics of these types of locomotion have been well analyzed but their energy cost is completely unknown.

　　Differences in the physical qualities of the media in which animals move account for such structural adaptations as streamlining of the body in flying and swimming animals, and the use of levers for propulsion in running animals. The weight of most swimming animals is fully supported by the surrounding medium, but running and flying animals must support the full weight of their bodies. The running animal has a solid support, but the flying animal must support its weight against a fluid of low density and low viscosity. In contrast, when the aquatic animal swims through water, it meets the resistance of a medium of high viscosity and density; running and flying animals have the advantage of moving in a medium of low viscosity and low density.

　　以上机经是康老师2011年10月－12月托福预测范围里的。