posted on May, 14 2008 @ 05:16 PM
Mabus, can't add too much more than ArMaP but some extra things to think about when regarding weight and gravity...
Originally posted by Mabus
Why is it the sun with its gravity wont pull in the planets with their gravities?
The real question is what determines the strength of gravity to an object? You weigh an amount here on earth, but on the moon or another planet I
heard you'd weigh different. What's up with that?
The strength of gravity is soley determined by the amount of mass (and therefore energy) an object has. This is because our current theory of
gravity, general relativity, tell us that what we experience as a gravitational force is really just a bending or curvature of spacetime caused
directly by the presence of matter or energy.
Don't get confused with weight and mass they are NOT the same thing at all. Rest mass of an object doesn't change weight is soley the product of
mass x gravitational field strength which is why an object can have the same mass here and on the earth but a different weight, the different weight
due of course to the fact that the moon is less massive and therefore less of a gravitational field.
Originally posted by Mabus
Why is it the sun with its gravity wont pull in the planets with their gravities?
By the way, if the sun was a solid surface planet would it still have the other planets orbiting it? And how much would you weigh if you could
stand on the sun if it wouldnt kill you like if it was a solid suface planet? Are there any discovered solar systems that dont have suns in their
center because they have a planet in the center?
(i). The sun having a solid surface is completley irrelevant to it's gravitational pull, it is simply the fact that it is so massive (compared to
the planets) that makes it the centre of gravitational focus for our solar system.
(ii). The solid surface question doesn't make much sense. Where are you going to place the solid surface? You can work it out, just take your mass
and multiply it by the gravitational field strength of the sun.
(iii). No there are no systems with planets at the centre because the stars are much more massive. You see when a gas cloud collapses to form a star
the material surrounding it is pulled into orbit around it (this is a very simplistic picture of course!) which may eventually form planets. Since
stars form first before planets the greater gravitational field of the star is established first and hence all objects formed after orbit the star.
Of course there are multiple star systems, binary and even trinary stars are known to have planets. (These systems must be strange places indeed,
imagine sunrise where a redgiant a blue star rise together, spectacular!) In this case the planets orbit a star and the stars orbit the common centre
of gravity. Hope this helps,
Timelike.
[edit on 14-5-2008 by timelike]