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The Basics
Drag is the force of resistance caused by air or liquid pressure. If you have ever put your hand out the window of a moving car and felt the wind pushing against it, or walked into the wind on a breezy day and noticed how hard it is to move forward, you have experienced drag.
Drag affects an object’s ability to travel through air or fluid in several ways. Drag slows an object down. It forces a powered object to use more fuel. Drag can even pull an object apart if it is not designed to withstand the force of drag.
Aerodynamic drag, which affects objects in flight, comes from two primary sources: form drag and friction drag.
Unlike this Boeing 767 airplane, a parachute is designed to increase drag to slow its descent.
Friction Drag
One source of drag is friction created by the movement of air or liquid as it crosses the surface of an object. This is called friction drag or surface drag. Rough surfaces create more drag than smooth surfaces. This is why engineers design aircraft with smooth, sleek surfaces.
Form Drag
The force needed to separate the air or liquid stream so it can go around an object is a source of drag. This is called form drag or pressure drag. The less streamlined an object is, the more force the air will exert; streamlined objects are less affected.
A shark has a smooth, streamlined shape
that reduces drag as it swims through the water,
much like a jet flying through the air.
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Try it yourself! Learn about drag with these easy and fun experiments. Adobe Acrobat® version (file size: 64 KB) Download Now |
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Download a printable, letter-size version of the classroom poster on drag. Adobe Acrobat® version (file size: 182 KB) Download Now |
Ludwig Prandtl, 1875–1953
German engineer and professor of applied mechanics whose work formed the basis for the modern science of aerodynamics.
