# COMMUNITY : FORUMS : SCIENCE

## My Theory for How Gravity Works

So I've never really found out how gravity actually works, why it happens. But a few days ago I had a epiphany. I don't know if I spelled that right. So everything is at least a little bit magnetic, even stuff like wood, no matter how little. So all of this stuff would be attracted to all the other stuff electromagnetically, right? Even a little bit? So when you get huge amounts of this stuff (I'm thinking planets here) there is enough electromagnetic attraction to pull it together, and voila! We have gravity! Plus when you have planets, there's tons of stuff like iron and other metals and metaloids, that could be very strong, magnetically. So if I'm wrong (which I probably am), can someone explain how gravity actually works to me? I'm constantly thinking about stuff like this, I get theories like this every once in a while, many of them right. But not this complicated, more stuff like figuring out how air pressure and vacuums work, but basic principle stuff.

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makes sense to me.i'm pretty gullible.
hungyhipo 27 years ago
basically what kiteman is saying is every object has mass and the more mass something has the more it has a pull on other objects so technically my computer is pulling me to it but the affect is so little that it can not be seen but the earth has so much mass that it pulls things down get it ok
Kiteman8 years ago
If you managed to properly describe gravity in terms of electromagnetism, you'd be more famous than Einstein!

The "simple" model is that gravity is not actually a force (although it's effects can be treated like one in Newtonian physics).

Instead, mass distorts spacetime; the more mass, the more bending.

This is the bit that plaits most peoples' minds: objects move in straight lines through spacetime, but because mass has distorted the spacetime, the straight lines are actually bent, so (to those animals that only evolved to see three dimensions of spacetime and live along the fourth, they appear to move in curves such as the arc of a thrown ball or the orbit of a Moon.
8 years ago
I understand his theory (at a low level), but in physics we've been talking about circles, including centripetal force. Does it have anything to do with gravity?
8 years ago
As Kiteman wrote, "it depends." The analysis of circular motion you are working through in class is completely general. You don't need to know what kind of force is involved, just that there is a force (specifically, a force applied perpendicular to the velocity. If it is always perpendicular to the velocity (as the velocity vector changes due to the force), it's called a central force.

For the problems you're solving, I'll bet that most of the time the central force you're considering is from a string, or maybe friction on car tires, or some such thing. Gravity is one particular example of a central force. It has the interesting added complication that it's not a fixed, constant force, but depends upon the distance from the center (1/r2).
8 years ago
For little circles, no, for big circles, yes - it depends what is providing the centripetal force - a piece of string, or the gravitational attraction of planets.

Kelsymh?
8 years ago
I forgot about that, the gravity would be the force
8 years ago
Minor nit-pick. You wrote, "objects move in straight lines through spacetime, but because mass has distorted the spacetime, the straight lines are actually bent..." That sort of paradoxical phrasing is inherently confusing, particularly to non-technical readers.

Trajectories in GR are curved, not straight: they have non-zero second derivative along the metric-element (ds) direction. Technically, they are called "geodesics" and are the paths of minimum or maximum distance through the curved spacetime. In particular, they are curved in the full four-dimensional spacetime, not just in the three-dimensional spatial slices of a particular rest frame.

A more familar example of geodesics (and the reason for the name!) involve minimum distance paths on the surface of the Earth. To get from point A to point B on the surface of a sphere in the shortest time (shortest distance at constant velocity) you want to follow a Great Circle trajectory. This path is the intersection of the plane defined by points A, B, and the center of the sphere, with the surface of the sphere.

The Great Circle path is curved in the "flat" three-dimensional space containing the sphere, but it is also curved in the frame of the spherical surface itself. Except for the special cases of travel along the Equator or directly North or South, any great circle route involves a constantly varying compass heading, and is therefore "curved" in the canonical East x North coordinate system.
8 years ago
I bow to your superior knowledge!

Guess where I'm I'm going to start passing all the physics questions on to?
8 years ago
>Jaw drops< I...buh...wha... kelseymh just replaced Kiteman as the head "Sciency" guy... *sniff* It's the end of an era...
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