The definition of a fulcrum is a pivot point around which a lever turns, or something that plays a central role in or is in the center of a situation or activity. 1  A pivot point around which a lever turns is an example of a fulcrum. 2  A person around whom all activity revolves is an example of the fulcrum.
Weightlessness, condition experienced while in free-fall, in which the effect of gravity is canceled by the inertial (e.g., centrifugal) force resulting from orbital flight. The term zero gravity is often used to describe such a condition. Excluding spaceflight, true weightlessness can be experienced only briefly, as in an airplane following a ballistic (i.e., parabolic) path. Crews of spacecraft are subject to the problems of weightlessness. It was learned from early Soviet and U.S. manned missions that there is a reduction in heart and respiration rates and a progressive loss of body weight and bone calcium during flights of relatively short duration.
AS HEAD of physics at Isaac Newton's old school, I am prompted by Mr Rowe's letter to write to explain the misunderstandings he apparently has. Neither an astronaut in orbit round the Earth nor the Moon, which is also in Earth orbit, is weightless, despite the frequent misleading use of the term.