Hiall. This might be a childish and stupid question, but today my litle brother was asked if he knew why the water didnt fall off the planet if its round (testing his knowledge i guess hehe), he responded with gravity.

If gravity can hold down such a mass of water, wouldnt that tremendous force crush us to the floor?

interesting, but no

for one, there is surface area displacement, so not every molecule is being draw to the ground at a single focal point. it is spread around a large surface area which makes up the earth
2ndly, we evolved on this planet. Somewhere in our evolutionary cycle we were able to overcome gravity, or it was never a problem. Evolution and the materials that came before life were able to be there without gravity destorying them.

Makes you wonder about jupiter though

Gravity is stronger as you get closer to the core.

Everything that has mass has gravity. If you have an orange floating in space (far out there without the influence of any other planets) the place some peas near the orange, they will be drawn to it.

Likewise, there may be small planets like this out there. So small that we could hold them in our hands.

And further likewise, there are planets that are millions of times more massive than this "Earth"

This post was edited by Torm1 on Jan 9 2011 11:18pm

as toothfairy said already too, we evolved on this planet. due to this, we evolved necessities such as ability to withstand such pressure. however, if you were to go a couple thousand feet below the ocean's surface, it would be a different story. hence why they have those enclosed suits that weigh like 500 lbs. (think its men of honor where they show a suit like that). also gravity holding down water, you should look more at molecules singularly and not as a mass.

its true... water stacks on water, weighing it down
as well the planet has a massive surface area and the water is spread out all around us (doesn't really matter if it was stacked up, it would still stay with us unless it left the thermospehere ya dig? ;P lol)
also we have most likely evolved to overcome gravity... thats why we have such a nice skeletal system, high blood pressure and nearly water-tight skin.

another interesting thing you should teach him about gravity and water could be the tides... and the role of the moon

buoyancy too is a interesting gravity related topic

inb4peoplestartdeningevolutionandsayinggoddidit

Actually, gravity gets weaker when you get closer to the core, and if you get to the exact center of the Earth, the Earth will exert no gravitational force on you:
http://en.wikipedia.org/wiki/Shell_theorem

Theoretically if you have an orange and a pea and no other forces are acting on either, then yes, they will attract, but the force will still be incredibly small, and if you were to put them a few feet away from each other they'd probably take quite a long time to actually come together (I don't feel like doing the math, though).


Nope. Small planets in our hand? Those wouldn't be planets. There is space debris like this in our solar system, though. Check out the Asteroid Belt some obvious examples.

As for super-large planets? The sun's mass is ~333,000 times the mass of the Earth. Anything that massive will be a star because it'll have enough pressure to begin nuclear fusion. Jupiter's a pretty big planet and it's only ~317 times more massive than Earth.