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Air drag12/9/2023 Note that C has no units, and to calculate force one must multiply by the area in the figure as well.60 Drag Forces on the Body A skydiver maintains a horizontal (flat) body position with arms and legs spread, which reduces the terminal velocity and increases the fall time. Figure 3 below shows the drag coefficient C for various shapes. For more details on how air drag is calculated please see NASA's site. It is usually determined experimentally, by taking measurements of an object in a wind chamber. The drag coefficient in the equation for drag is quite complex, and depends on various factors such as those listed above, and also includes air viscosity and how compressible a fluid is. The wind slows down upon contact with the turbine and these collisions combined with the shape of the turbine blades allows it to spin, providing wind power. It might seem strange that a stationary object can be affected by air drag, but air drag occurs when there is a relative motion between the air and the object, so it can be viewed as if the turbine is moving through the stationary wind. The flow of air through a wind turbine causes the turbine to spin, because of the collision of the particles and the turbine. This equation is an approximation and only works for ordinary objects (with a size between a few millimeters and a few meters) and ordinary speeds (no more than a several meters per second), so it fails to describe the motion of very small objects like dust, or very fast objects like bullets. ![]()
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