Types of Drag
Types of drag are generally divided into the following categories:
- parasitic drag, consisting of
- form drag,
- skin friction,
- interference drag,
- lift-induced drag, and
- wave drag (aerodynamics) or wave resistance (ship hydrodynamics).
The phrase parasitic drag is mainly used in aerodynamics, since for lifting wings drag is in general small compared to lift. For flow around bluff bodies, drag is most often dominating, and then the qualifier "parasitic" is meaningless. Form drag, skin friction and interference drag on bluff bodies are not coined as being elements of "parasitic drag", but directly as elements of drag.
Further, lift-induced drag is only relevant when wings or a lifting body are present, and is therefore usually discussed either in the aviation perspective of drag, or in the design of either semi-planing or planing hulls. Wave drag occurs when a solid object is moving through a fluid at or near the speed of sound in that fluid—or in case there is a freely-moving fluid surface with surface waves radiating from the object, e.g. from a ship.
For high velocities—or more precisely, at high Reynolds numbers—the overall drag of an object is characterized by a dimensionless number called the drag coefficient, and is calculated using the drag equation. Assuming a more-or-less constant drag coefficient, drag will vary as the square of velocity. Thus, the resultant power needed to overcome this drag will vary as the cube of velocity. The standard equation for drag is one half the coefficient of drag multiplied by the fluid mass density, the cross sectional area of the specified item, and the square of the velocity.
Wind resistance is a layman's term for drag. Its use is often vague, and is usually used in a relative sense (e.g. a badminton shuttlecock has more wind resistance than a squash ball).
Read more about this topic: Drag (physics)
Famous quotes containing the words types of, types and/or drag:
“Science is intimately integrated with the whole social structure and cultural tradition. They mutually support one other—only in certain types of society can science flourish, and conversely without a continuous and healthy development and application of science such a society cannot function properly.”
—Talcott Parsons (1902–1979)
“The rank and file have let their servants become their masters and dictators.... Provision should be made in all union constitutions for the recall of leaders. Big salaries should not be paid. Career hunters should be driven out, as well as leaders who use labor for political ends. These types are menaces to the advancement of labor.”
—Mother Jones (1830–1930)
“Dying smokers sense
Walking towards them through some dappled park
As if on water that unfocused she
No match lit up, nor drag ever brought near....”
—Philip Larkin (1922–1986)