Word: wing tip
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Dates: during 1888-1888
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...when the force is slowly applied. When a force is exerted suddenly, considerable resistance is offered even by as mobile a body as air. Birds are enabled to fly only by the resistance of the air during the downward stroke of the wings. During the upward stroke, less resistance is offered, owing to the fact that the wing is convex on the upper side, and is at the same time contracted in area, thus moving with less velocity. In fact instantaneous photographs show that it takes twice the time to complete the upstroke that is needed for the downstroke. Unless...