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Why doesn't the moon crashes into the earth or the earth into the sun?

They have a velocity that tries to move them further apart from the central body (say the sun) but at the same time are attracted towards it. The two effects roughly compensate. Note that in principle it may well happen that the moon crashes into earth - and that it merely takes a lot of time to happen.

 

Is the answer same as for the question "Why doesn't the electron meets with the nucleus?"

No.

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They have a velocity that tries to move them further apart from the central body (say the sun) but at the same time are attracted towards it. The two effects roughly compensate.

Did you meant centripetal,centrifugal or gravity forces?

Edited by akash shrestha
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Did you meant centripetal,centrifugal or gravity forces?

 

Why confuse matters with centripetal and centrifugal forces? Just gravity and inertia are in relative equalibrium for the planets. However, over Billions of years, the planets and moons will be located differently, and the Sun will swell up as a red giant.

 

Why doesn't the moon crashes into the earth or the earth into the sun?Is the answer same as for the question "Why doesn't the electron meets with the nucleas loosing its kinetic energy, in an atom?"?

 

I think you have a point, but I may be wrong since I am not expert. Electrons follow their orbits because of their energy level, and planets follow their orbits because of their energy level (inertia).

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Electrons follow their orbits because of their energy level, and planets follow their orbits because of their energy level (inertia).

It is possible that object A with an energy of E orbits the sun while another object B with the same energy E crashes into the sun. In other words: the energy level does not (exclusively) determine whether a stellar object crashes into the sun, orbits it, or is slightly bent in its curve but leaves the solar system (like I guess some comets do). The statement "electrons follow their orbits because of their energy level" is slightly problematic, as it can be understood to imply that having a certain energy is the cause for some orbit. It is probably better to think of it the other way round (a certain energy being the effect of being in an orbit - whatever an electron orbit may be): Electrons follow orbits, orbits have an energy associated to them. Therefore, an electron following an orbit has some (specific) energy. Notice that there is a subtle difference, e.g. that in the latter picture two different orbits can in principle have the same energy - similarly as the planet orbiting the sun and the planet crashing into the sun can have the same energy.

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The physics of the earth and moon orbits is completely different from what happens inside an atom.

 

The celestial orbits are governed by Newton's laws of gravity (or General Relativity to be precise).

 

The interactions describing the atom are described by quantum mechanics. These relationships should not be viewed as orbits in the same way as the celestial. Instead the description is in terms of quantum states.

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Note that in principle it may well happen that the moon crashes into earth - and that it merely takes a lot of time to happen.

 

It seems on present evidence that over time the distance between the moon and earth will increase. It is presently increasing at a rate of approximately 4cm per year. http://www.physlink.com/education/askexperts/ae429.cfm

Edited by TonyMcC
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If the sun consumes itself, How is it still holding onto all those planets after 4.5 billion years?

The sun has enough hydrogen to keep going for another 4.5 billion years. It will then turn into a red giant and probably eat the earth.

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