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The basic question "Why planets revolve around the Sun?", is explained by taking into account the heaviness of Sun. The lighter bodies are considered to move around heavier bodies,as like lighter planets are considered to move around heavier Sun.

The reason for lighter bodies moving around heavier bodies is said to be because of greater gravitational pull exerted by heavier bodies. But, I don't know why heavier bodies produce greater gravitational pull than lighter bodes.

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    $\begingroup$ As written, this question implies a child-like understanding of gravity. $\endgroup$ – Alfred Centauri Oct 21 '13 at 13:00
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    $\begingroup$ Actually bodies orbit around their common center of mass. It just happens that when one body is much larger than all the others it can be well approximated as the center of mass of the whole system. For example the center of mass of the solar system is well inside the sun. $\endgroup$ – Michael Brown Oct 21 '13 at 13:02
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    $\begingroup$ @AlfredCentauri.Suppose if we had not known about gravity,and if Newton would have asked Alfred "Why an apple always falls down from the tree?".I think Alfred would have responded to Newton "you are having child-like understading".Alfred would had not known that child like understanding question is going to end with the theory of gravitation.Remember every one are still child in understanding nature. $\endgroup$ – Immortal Player Oct 21 '13 at 13:25
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But,I don't know why heavier bodies produce greater gravitational pull than lighter bodes.

"Heavier" (more massive) bodies produce a stronger gravitational field than "lighter" (less massive) bodies.

But, two bodies, one much more massive than the other, exert the same gravitational "pull" (force) on each other.

This follows from Newton's Law of Universal Gravitation (from Wiki):

enter image description here

So, the "pull" is the same on each but, if one body is much more massive than the other, the force accelerates the more massive body far less than the other. This is why, in the case of the Sun and planets, it is the planets that seem to orbit a (near) motionless Sun.

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  • $\begingroup$ I had not seen your answer while working on mine. As mine is a different pov I will leave it in. $\endgroup$ – anna v Oct 21 '13 at 13:31
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Because gravitationnal forces always add up (unlike electrical force from positive and negative charges, for example), so as you add mass you always increase force.

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  • $\begingroup$ think. if you increase charge do you not increase the force either attractive for unlike of repulsvie for like? $\endgroup$ – anna v Oct 21 '13 at 14:22
  • $\begingroup$ yes of course you do, but there is no large body of same-sign charges that, if growing, will have more of its charge. That's because, no matter what, when growing such a body will end up attracting opposite charges. For gravitation, adding matter will increase mass. That's, for me, the reason why gravitation always wins when looking towards larger scales. $\endgroup$ – Nicolas Oct 21 '13 at 14:30
  • $\begingroup$ Actually, as you add mass, the volume and diameter of the body will also grow, and thus the surface gravity will not grow as fast. But for rocky bodies (including planets, moons, asteroids) the mass grows with the third power of the radius, while gravity decreases with the second power. $\endgroup$ – MSalters Dec 13 '17 at 14:37
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The basic question "Why planets revolve around the sun?", is explained by taking into account the heaviness of Sun.

No, the basic question that science has been able to answer is : How planets revolve around the sun, not Why.

This means that a mathematical model of assuming heavier masses attract more led to the central force of gravity formula of Neutonian gravity:

gravity

The two masses contribute proportionately to their value.

The observation was that planets are ordered about the sun according to their masses and Neutonian gravitation showed us how we could model their motion and predict motions of other celestial bodies using the proposed theory.

So the theory can answer why the earth has a large radius orbit around the center of mass of the solar system and the sun a small one, but in the end the why large masses contribute more than small ones to the force between two masses. ends up to the answer "because that is what our observations have told us" .

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