(Related to Textbook Section 9.3.3 - Drag Coefficient Data and Examples)
The drag coefficient for an object can be strongly dependent on the shape of the object. A slight change in shape may produce a considerable change in drag.
When falling at terminal (steady) speed, a sky diver's weight is balanced by the aerodynamic drag. If the air speed in a vertical wind tunnel equals the terminal speed, the sky diver can remain motionless. Any change in shape (bend or straighten arms or legs, rotate a hand, etc.) alters the drag coefficient (and the drag) and causes the sky diver to rise, fall, or rotate until an equilibrium configuration is again produced. (Video courtesy of Flyaway.)
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