What exactly is gravity?

Question

What is the actual definition of "gravity." We all know how gravity works and it's effects. But nobody really "knows" what gravity is and why large masses attract other masses.

many seem to give me the formula. i know the formula. but that doesn't explain how it could happen. it just shows that we can measure gravity. but it does not give us the definition of it

and telling me that it holds us to the earth is not an answer!!!! that is just the effect it has! but not the definition!!!!

Answer 1

Hello Kenton -

Well - that's a good question. Newton thought of gravity as a force, and he developed the equations that describe it, complete with a fudge factor G, that he basically admitted was not the full description of the phenomenon.

Einstein came along and figured out that it isn't really a force, it just acts like one when objects are observed in a gravitational field. It is essentially the warping of spacetime (by mass) in such a way that objects do not travel in straight lines in 3D space.

Think of it this way: two spacecraft are each occupied by a single pilot standing on the floor. Neither spacecraft has any windows. One is in deep space and is accelerating at 1g. The other is sitting statically on the surface of the earth, where it is subjected to the earth's gravitational field. Einstein noted that the pilots cannot tell the difference between these two scenarios. Then he figured out that THAT'S BECAUSE THERE REALLY IS NO DIFFERENCE. The surface of the earth provides a force to prevent us from falling through it toward the center of the earth, just as the engines provide a force to accelerate the spacecraft in empty space. Now think about if the surface suddenly turned to empty space, but the earth's mass remained concentrated at the core. You would suddenly start to fall inward in a weightless condition. You would not feel the effects of acceleration, or force, as you would in a car or a jet. You would not feel a push on your back; your head would not snap back. There are no forces acting on you in the normal sense of the word. It is the local curvature of spacetime that creates this condition, where the straightest line that you can travel without an outside force acting on you is not necessarily a straight line in 3D space (as Newton said), but is generally skewed toward the most massive object around. In this case, the object is not really applying a force, it's just changing what is meant by a "straight" line with no external force. In order to keep from moving in this direction (i.e. toward the center of the earth) you must apply an opposing force to keep from falling inward. This can be done by throttling up your engines at 1g, or by sitting on the surface with 1g pressing up against your feet.

Now, this is not really useful when solving most physics problems, because the Newtonian description works quite well. That is, an object floats in orbit because the "centripetal force" of gravity is just sufficient to bend a straight path into a curved one. But there really is no force - it's just a convenient way to attack the problem.

Answer 2

Things with mass are attracted to other things with mass. The confusing part is that while the other forces have an associated particle, the carrier particle for gravity has not been observed. To be exact, it's a mystery. If and when someone answers this, they'll be up for a Nobel prize, not prattling on about it here.

Answer 3

Gravity is the force that holds you to the surface of the Earth

Answer 4

We still don't fully understand what is gravity. Some says it is due to some mysterious "graviton" particles while other tends on the space-time curve theory (which is true but doens't explain how gravity works anyways)

Answer 5

omg! we're learning about gravity in class!!

gravity is the force that objects exert on each other because of their masses

i really don't know how to explain gravity. sorry...

Answer 6

Gravity is a force

Answer 7

enables you to walk on a surface on earth while it may make you float on the moon or in space where gravity is a rare luxury

Answer 8

force with acceleration 9.8 m/s2
"The natural force of attraction between any two massive bodies, which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them."
Dictionary.com

Answer 9

each of them have there gravitional accleration like earth is 9.8m/s^2 or 10. Depending on mass and desinty its different

Answer 10

I thought it was a force and an acceleration. -9.80m/s/s
Right??