2011-12-07, 03:43 AM
Kalovale Wrote:I don't quite grasp this. What's a "rocky planet"? Gravity should be strongest at infinitesimally close to the core, shouldn't it? Or am I interpreting it the other way, and it should be read "gravity caused by a rocky planet (as opposed to gaseous or liquidy ones) is generally the strongest when compared at the surface"?
Think about it for a bit.
Ignoring all other matter, if planet A was really far away, it's a no-brainer to say that the direction of gravity from your perspective is towards planet A. Now throw planet B into the mix, which has the same mass and size (for simplicity's sake). If you were equidistant between these two planets, the net gravitational pull on you is zero. Throw planet C into the mix, which is just as far away from you, and all other planets are the same distance away from each other as well as being identical in mass and size. Net gravitational pull is still zero. We can keep on doing this for a however many planets.
Now imagine that you are in the center of a planet, ignoring all other matter. How will gravity pull at you? Because there's an equal amount of matter at any given distance away from you in all directions, the net gravitational pull is zero.
The thing about reality is, with the exception of black holes, it's not really accurate to treat bodies as a point mass. The way the educational system teaches it gets you "good enough" results (negligible difference) if you're sufficiently far away from something, just like how we don't factor in time distortion if we're moving at 200mph across Utah's salt flats.