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.
Weight refers to the force experienced by an object due to gravity. Mass refers to the amount of matter in an object. An object with a mass of 1 kilogram will weigh approximately 9.81 newtons. (newton is a unit of force) Mass is also an inertial property meaning the tendency of an object to remain at a constant velocity unless acted upon by an outside force.