Rusk, Rogers D. Formerly, Department of Physics, Mount Holyoke College, South Hadley, Massachusetts.
Last reviewed:April 2019
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The motion of a body acted on by gravitational attraction and by no other force. Bodies in free fall experience weightlessness, a condition induced by the effective lack of resistance to gravitational force. Although this condition is sometimes referred to as zero gravity or microgravity, these terms are misnomers, because gravity does exist in space. Free fall is described in physics by Newtonian mechanics and Einsteinian general relativity. In many cases, the term is invoked to describe bodies accelerating toward the center of Earth's gravity, either through the atmosphere (Fig. 1) or in orbit around the planet, including artificial satellites, such as the International Space Station, and the natural satellite of the Moon. Isaac Newton's perception that the Moon must be in continual free fall toward Earth led the English physicist and mathematician to develop his universal law of gravitation in 1685 CE. See also: Acceleration; Center of gravity; Earth; Gravity; Moon; Newton's laws of motion; Planet; Relativity; Relativistic mechanics; Satellite (astronomy); Satellite (spacecraft); Space flight; Space station; Weightlessness
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