Drag
(vehicle)
Drag
is the resistance or retarding force that an object, such
as an automobile, experiences as it passes through the air.
Drag is made up of two components, one due to pressure and
the other due to friction. Pressure-related drag arises from
the difference in air pressure between the front and rear
surfaces of the body. This has to be overcome to keep the
body moving through the air, and is particularly significant
in the case of relatively flat-surfaced, bulky objects such
as motor vehicles. If the body moving through the air is slender
and streamlined, however, like a modern aircraft, resistance
due to friction represents a higher proportion of total aerodynamic
drag. It is caused by the airflow rubbing against the surfaces
as it passes over them. Aerodynamic drag increases as the
square of the air speed, in other words if the speed doubles,
the drag increases fourfold; if the speed quadruples it increases
sixteen-fold, and so on. A specific example of this: as a
car accelerates from 100 to 141 km/h, the aerodynamic drag
doubles. See also drag coefficient.
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