[Q] Gravity

[Rob Galaxy]

What is gravity?

[CraigD]

Gravity is the mutually attractive force between 2 bodies directly proportional to the product of their masses [math]m_1[/math] and [math]m_2[/math] and inversely proportional to the square of the distance between [math]r[/math] them – stated mathematically, [math]F = \frac{G m_1 m_2}{r^2}[/math].

 

Although this simple 17th century definition – Newtonian gravity - describes gravity to a reasonable approximation adequate for most practical purposes, general relativity describes if better.

 

Note that both Newtonian gravity and general relativity are empirical laws, telling us what gravity is, but making no attempt to tell us why. Although much scientific work has been done toward answering this “why” question (major areas of research include quantum gravity and string theory), so far no explanation has been very successful or widely accepted.

[NLN]

In layman terms, gravity is a natural phenomenon by which objects with mass attract one another. In everyday life, gravity is most commonly thought of as the agency which lends weight to objects with mass. Gravitation compels dispersed matter to coalesce, thus it accounts for the very existence of the Earth, the Sun, and most of the macroscopic objects in the universe. It is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth, for the formation of tides; for convection (by which hot fluids rise); for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena that we observe.

 

As the previous answer noted, modern physics describes gravitation using the general theory of relativity, in which gravitation is a consequence of the curvature of spacetime which governs the motion of inertial objects. The simpler Newton's law of universal gravitation provides an excellent approximation for most calculations.

 

Machines Like Us

[enorbet2]

If you enjoy having your mind blown read any of the new books on the attempt to unify gravity with the other 3 forces (resolving why gravity seems so weak by comparison) hoping to bring the macrocosm and the microcosm together. Wiki is OK but I recommend Lee Smolin's "Three Roads to Quantum Gravity" which instead of a compendium is a fairly linear and coherent effort to explain deep theory in a way an amateur can grasp but it will likely twist you up before you disentangle. Quite a romp.

[maddog]

Wiki is OK but I recommend Lee Smolin's "Three Roads to Quantum Gravity" which instead of a compendium is a fairly linear and coherent effort to explain deep theory in a way an amateur can grasp but it will likely twist you up before you disentangle.

I read Smolin's book, excellent! Also, I would recommend Roger Penrose's book, "Road to Reality". I will admit this is a bit more rigorous. Also, excellent read.

 

 

maddog