# gravity

[grav-i-tee]

## Origin of gravity

## Synonyms for gravity

Dictionary.com Unabridged
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

## gravity

## Word Origin for gravity

C16: from Latin gravitās weight, from gravis heavy

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
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## gravity

Online Etymology Dictionary, © 2010 Douglas Harper

## gravity

[grăv′ĭ-tē]

A Closer Look: With his law of universal gravitation, Sir Isaac Newton described gravity as the mutual attraction between any two bodies in the universe. He developed an equation describing an instantaneous gravitational effect that any two objects, no matter how far apart or how small, exert on each other. These effects diminish as the distance between the objects gets larger and as the masses of the objects get smaller. His theory explained both the trajectory of a falling apple and the motion of the planets-hitherto completely unconnected phenomena-using the same equations. Albert Einstein developed the first revision of these ideas. Einstein needed to extend his theory of Special Relativity to be able to understand cases in which bodies were subject to forces and acceleration, as in the case of gravity. According to Special Relativity, however, the instantaneous gravitational effects in Newton's theory would not be possible, for to act instantaneously, gravity would have to travel at infinite velocities, faster than the speed of light, the upper limit of velocity in Special Relativity. To overcome these inconsistencies, Einstein developed the theory of General Relativity, which connected gravity, mass, and acceleration in a new manner. Imagine, he said, an astronaut standing in a stationary rocket on the Earth. Because of the Earth's gravity, his feet are pressed against the rocket's floor with a force equal to his weight. Now imagine him in the same rocket, this time accelerating in outer space, far from any significant gravity. The accelerating rocket pushing against his feet creates a force indistinguishable from that of a gravitational field. Developing this principle of equivalence, Einstein showed that mass itself forms curves in space and time and that the effects of gravity are related to the trajectories taken by objects-even objects without mass, such as light. Whether gravity can be united with the other fundamental forces understood in quantum mechanics remains unclear.

The American Heritage® Science Dictionary
Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

## gravity

The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.