Quote:
Originally Posted by pilgrim
If the mass of the star mass was a point particle at the centre the force you would feel would be much greater because you would be closer to the mass. However, the star is an extended object so if you were a particle inside the star you would see the centre and most of the mass to your one side but now there would be some considerable mass (the outer layer of the star you had to go through to get tothis point in the star) on your other side as well. This would have 2 effects. Firstly now there is less mass pulling you towards the centre of the star (smaller gravitational force) and secondly there is now also some mass pulling you in the opposite direction so in effect the force towards the centre you feel at that point is lesser than if there was a point particle of the star's mass at the centre.
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You're right.
It turns out that if you're somehow embedded in a spherically symmetrical mass-distribution, the gravitational force you feel is easily calculated. You feel
only the gravity of the matter that lies at a smaller radial distance from the centre than your own distance.
All the matter lying farther out than your radius exerts no net gravitational force on you -- a consequence of the fact that the gravitational force within a spherical shell cancels down to zero at all points enclosed by the shell.
Grant Hutchison