Which Way is "dn" or the 'Force of Gravity' in Some Simple Accelerated Systems
Albert Allen Bartlett · The Physics Teacher · 1972
Everyone uses the words "up" and "down." There is little ambiguity about their use when one thinks of experiments performed in a coordinate system that is at rest with respect to the surface of the earth. In a more complicated system, however, such as an accelerating car or elevator, a merry-go-round, or an orbiting satellite, an observer will have a perception of "up" that may be quite different from that of an observer at rest. Let us examine some of these perceptions.