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Net aerodynamic or hydrodynamic force: Drag acting opposite to the direction of movement of a solid object such as cars, aircraft, [3] and boat hulls. Viscous drag of fluid in a pipe: Drag force on the immobile pipe decreases fluid velocity relative to the pipe. [4] [5]
The force on an object that resists its motion through a fluid is called drag. When the fluid is a gas like air, it is called aerodynamic drag or air resistance . When the fluid is a liquid like water it is called hydrodynamic drag, but never "water resistance".
For most large objects such as bicyclists, cars, and baseballs not moving too slowly, the magnitude of the drag force \(F_D\) is found to be proportional to the square of the speed of the object. We can write this relationship mathematically as \(F_D\propto v^2 \).
Air resistance is an example of a drag force which objects experience when moving through the air. At a walking pace, a person rarely experiences the effects of air resistance. However, a person swimming at the same pace uses up much more energy - this is because air is 800 times less dense than water.
At highway speeds, over 50 % 50 % of the power of a car is used to overcome air drag. The most fuel-efficient cruising speed is about 70–80 km/h (about 45–50 mi/h). For this reason, during the 1970s oil crisis in the United States, maximum speeds on highways were set at about 90 km/h (55 mi/h).
Air friction, or air drag, is an example of fluid friction. Unlike the standard model of surface friction, such friction forces are velocity dependent. The velocity dependence may be very complicated, and only special cases can be treated analytically.
4 Μαρ 2017 · The forces that a moving vehicle must overcome are the tire rolling resistance, the driveline friction, elevation, vehicle acceleration changes, and also aerodynamics. Let us assume that the vehicle moves along a flat surface at a constant speed and the external forces are limited to the tire friction and to the aerodynamic drag.
