Gravitational force means"the force experienced between two heavenly bodies".A body falls on any planet due to gravitational force.But smaller planets are not attracted by larger planets or stars(sun) due to this force. What is the reason for this?
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asked Apr 5, 2017 at 4:00
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2$\begingroup$ Possible duplicate of Why doesn't the Moon fall upon Earth? $\endgroup$– RuslanCommented Apr 5, 2017 at 4:59
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$\begingroup$ Duplicate #2: physics.stackexchange.com/q/312492 $\endgroup$– YashasCommented Apr 5, 2017 at 7:29
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1$\begingroup$ This is a new question, and has a simple answer : the earth and the sun and all the planets move about the center of mass of the solar system. Everything moves!. $\endgroup$– anna vCommented Apr 5, 2017 at 11:35
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1$\begingroup$ Please do not make edits that change your question entirely, especially after answers have been given, but ask a new question instead $\endgroup$– ACuriousMind ♦Commented Apr 5, 2017 at 12:12
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$\begingroup$ Hi DARYL JOSEPH G, Welcome to Phys.SE. Echoing what @ACuriousMind said I roll back the question to v2. Oh, he already did it. $\endgroup$– Qmechanic ♦Commented Apr 5, 2017 at 12:14
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3 Answers
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Tie a weight to a string.
Pull on the string. The weight hits you. You are doing to the weight what gravity does.
Now swing the weight in a circle. You are still pulling the weight toward you, doing what gravity does.
answered Apr 5, 2017 at 4:53
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Newton was the first to connect "falling motion" and the motion of "heavenly bodies". He said these two motions had the same origin: the gravitational force. But to explain how the Earth and other heavenly bodies do not fall, while the apple does, he needed to define how motion works and what quantities are involved. In what are now known as Newton's laws (because they seem to hold for all bodies) he said that bodies can and will move in a straight line with constant velocity if no forces are present, and the effect of forces acting simultaneously is such as if only one force was acting, equal to their sum. Whatever the force, its effect is a change in the motion of the body, possibly in both direction and magnitude. Finally he stated that if a body exerts a force upon another, it will in turn be subjected to an equal and opposite force. These elements, expressed mathematically, allow to describe exactly the motions of the falling apple and the heavenly bodies under their respective conditions.
But to answer your question maybe math is not necessary if we think of similar examples. While a force changes motion, it cannot avoid the inertia of the body, its tendency to "go as it was going". So a force applied sideways to the direction of motion will make it turn (slower or faster depending on how strong the force is compared to how fast the initial motion was). But by the time the turn happens, the body has moved forward a bit. Similarly when turning on a car, the friction of the street on the side of the wheel pushes it sideways, but does not make it turn in place, unless the force is strong enough. In such a way, the Earth is moving away from the Sun whose force acts sideways to the motion, but it can only make it turn a bit every time the Earth moves forward. Unlike the car, the Earth is moving in a frictionless space and loses almost no energy in its motion, so unlike the car, its forward motion is sustained for extremely long time.
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As Earth has tangential velocity it will not be pulled into the Sun, but will go into orbit. If it had little or no tangential velocity then it would be pulled into the Sun.
