Quote (Kazuki @ Fri, Apr 17 2009, 11:21pm)

There are two forces in nature that we experience every day: gravity and magnetism. You may have magnets on your refrigerator, and you know that a magnet will attract a refrigerator with a certain amount of force. The force depends on the strength of the magnet and the distance between the magnet and the metal. You also know that magnets have two poles -- north and south. Either pole will attract iron or steel equally well, north will attract south, and like poles will repel one another.Gravity is the other common force. Newton was the first person to study it seriously, and he came up with the law of universal gravitation:

Each particle of matter attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

The standard formula for gravity is:

Gravitational force = (G * m1 * m2) / (d2)

where G is the gravitational constant, m1 and m2 are the masses of the two objects for which you are calculating the force, and d is the distance between the centers of gravity of the two masses.

Quote (heepajunk @ Sun, Apr 12 2009, 03:54am)

While gravity is very well described by theory as the effect mass and energy have on spacetime, it is still unclear how this fits in with our other accurate descriptions of reality, i.e. waves and particles.
This is currently one of the biggest problems confronting modern physics, and to complicate matters there seems to be more gravity and energy in the universe than visible matter can account for.

So basically we're shit out of luck until we can harvest massive amounts of experimental data to test front-running theories - like string theory - which have yet to be subjected to nature's arbitration 
Time will tell.

Quote (sillybillyxp @ Fri, 17 Apr 2009, 01:32)

It'll help if you envision the universe as a big blanket (this represents space). If you lob a large, heavy object onto that blanket, it will push the blanket down. Then, if you roll a ball along the now inclined-surface surrounding that heavy object, it will accelerate. In fact, it accelerates faster if the object is heavier, as heavier objects will cause more of a slope in that inclined surface. That's the impact of gravitational acceleration and the mass of the object: heavier/denser object = larger g. I guess that effectively explains it.

Quote (Crematoria @ Sun, Apr 12 2009, 12:07pm)

Gravitation is a natural phenomenon by which objects with mass attract one another. In everyday life, gravitation 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 fluid flow occurs under the influence of a temperature gradient and gravity); for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena that we observe. 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.

The terms gravitation and gravity are mostly interchangeable in everyday use, but a distinction may be made in scientific usage. "Gravitation" is a general term describing the phenomenon by which bodies with mass are attracted to one another, while "gravity" refers specifically to the net force exerted by the Earth on objects in its vicinity as well as by other factors, such as the Earth's rotation.

Quote (sillybillyxp @ Thu, Apr 16 2009, 11:32pm)

It'll help if you envision the universe as a big blanket (this represents space). If you lob a large, heavy object onto that blanket, it will push the blanket down. Then, if you roll a ball along the now inclined-surface surrounding that heavy object, it will accelerate. In fact, it accelerates faster if the object is heavier, as heavier objects will cause more of a slope in that inclined surface. That's the impact of gravitational acceleration and the mass of the object: heavier/denser object = larger g. I guess that effectively explains it.

Quote (jimmy123 @ Thu, Apr 16 2009, 05:16pm)

gravity is a force pulling together all matter (which is anything you can physically touch). the more matter, the more gravity, so things that have a lot of matter such as planets and moons and stars pull more strongly.