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Part one: 科技英语文体特征 Stylistic Features of EST (English for Science and Technology) Aerodynamics in Car Design Automobile designers are working on ways to build automobiles that get good gas mileage. One way to do this is to make cars more streamlined by reducing drag or wind resistance. Scientists define drag as a force that retards, or slows, an object that is moving through the air. All moving objects are subject to drag. Studies estimate that at 88 kilometers an hour, one-half of the car’s fuel and more than 60 percent of the car’s horsepower are used to overcome drag. So if car designers can reduce drag they can improve on the car’s gas mileage, or fuel efficiency. To find out more about drag, car designers use engineers who are specialists in aerodynamics. Aerodynamics is a science that involves the study of moving air and the forces that act on objects moving through the air. The aerodynamics specialists measure air resistance in units indicating coefficient of drag, or CD. The coefficient of drag is the ratio of the amount of wind resistance an object encounters to that of a flat plate of the same weight held vertically. As an example of CD, a 1.2-by 2.4-meter piece of plywood held vertically would have a CD of about 1.1. Other shapes would have a lower CD. A watermelon of the same weight as the plywood would have a lower CD. A falling parachute would have a CD of about 1.3. In comparison, the typical automobile would have a CD of about 0.45. Wind Tunnels: The Basic Tool Engineers use wind tunnels to study the CD of automobiles. Wind tunnels are the basic tool of aerodynamic research. They are used to test design models, or smaller representations, of bridges, buildings, spacecraft, and most recently, automobiles. A wind tunnel can have a width of 12 to 24 meters and be as long as 275 meters. The tunnel has a special section where a test model is placed. The object tested can be a full-size car or a clay model of the real thing. A huge fan blows air into