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The Sun has a strong gravity. The planets also have gravity. So they attract each other. But then why dont they go and mix up with the Sun?

If it is the orbit of the planets or a pre-existing motion of a planet, then what is the reason behind this kind of motion? How did they happen to maintain the balance when there is no other force acting on the planets (except the sun)?

Lets say, somehow they had their motion from the very starting point. But now there is the gravity of sun acting on them, which means this pre-existing force will keep reducing until it vanishes. So after some time is passed, there would not be any balance in the solar system and thus they are supposed to fall down in the sun. But in reality that doesnt happen. So what is the reason and explanation?

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The planets do fall towards the sun. Constantly. But they miss. Constantly.

  • Place a satellite high above the ground. It falls and crashes.

  • Now, throw it lightly sideways with a sideways speed. It falls and crashes but farther to the side.

  • Throw harder sideways so the sideways speed is greater. It crashes much farther to the side.

  • Now throw very, very hard so a very, very large sideways speed is achieved. It now "falls past" Earth! It falls but misses!

The satellite will now attain an elliptic orbit. Give it an even larger sideways speed, and the ellipsis flattens. At some sideways speed that is just right, the ellipsis becomes a perfect circle - you now have a circular orbit.

We observe the planets in our solar system to move in elliptic or close-to-circular orbits. They constantly fall towards the Sun, but they also constantly miss and "fall past" it. And this is how orbits can keep up for millions and billions of years.

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    $\begingroup$ Great answer Steeven. But can you tell me what causes this great velocity of the planets for which they do not fall down in the sun? $\endgroup$
    – Arafat
    Commented Dec 29, 2022 at 14:10
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    $\begingroup$ @Arafat Gravity is a force, so dictates acceleration, but velocity is a separate question. When velocity is parallel (perpendicular) to acceleration, the path is linear (circular). It's orbits closer to the latter extreme that last a long time, although they're slightly elliptical in practice. Another way to explain it is their angular momentum, a consequence of the Solar system's early formation, is much too high for them to fall inward. $\endgroup$
    – J.G.
    Commented Dec 29, 2022 at 15:02
  • $\begingroup$ @Arafat If som celestial process throws a bunch of rocks towards the sun, then some will fly into he sun, others will fly away, and some might just by chance start orbiting because their velocities by coincidence happen to fit. As long as nothing stops them, then these orbits will keep up. Some might eventually crash together or other celestial events might happen. Those that remain will be called planets, moons or similar. And after billions of years we now have eight planets and many more bodies orbiting our sun in our solar system. And it all started by chance acoording to this idea. $\endgroup$
    – Steeven
    Commented Dec 29, 2022 at 15:21
  • $\begingroup$ I understand this part Steeven. But someone has to throw those rocks. My question is who threw those? How did these planets get that pre-existing motion that we are comparing with someone who threw the rocks? $\endgroup$
    – Arafat
    Commented Dec 29, 2022 at 15:28
  • $\begingroup$ @Arafat Well, a theory states that everything started with the Big Bang which formed space and threw matter into the world. This matter with associated energies would over time interact in various different ways. That's what eventually would form solar system, galaxies, clusters etc. What caused the original Big Bang to take place is not something we have an answer to. $\endgroup$
    – Steeven
    Commented Dec 29, 2022 at 16:46

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