## Why doesn't the moon fall on earth?

I am curious as to why the moon doesn't fall into the earth. Did a few searches and found:

http://www.physicsforums.com/archive...he_earth?.html

But that doesn't explain one thing.

Moons orbit is not an exact circle. Its "almost" circular. So when the moon is closest towards earth, shouldn't earths gravitational force on moon be stronger resulting in a spiral down-fall and eventally moon crashing into the earth?

And a similar question: why doesn't the earth fall into the sun? Earths orbit is even more oblique. So shouldn't the sun attract earth with greater force when it is nearer on days of equinoxes and eventually lead to a spiral down fall too?
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 Recognitions: Gold Member Homework Help Science Advisor When the moon is closest to the Earth, it's also travelling "sideways" at its fastest rate. This is generally true for any elliptical orbit. An extreme case is that of a comet, such as Halley's comet. When it is close to the Sun, it travels at such a high speed that it takes less than a year to go a fair portion of the distance around, but when it's far away it takes another 75 years to return again. Why? Because it slows down as it gets further from the sun. You're right that the attractive force of gravity is greater when the moon is closer to the Earth, but the extra speed compensates for the extra pull, and the moon still "misses" the Earth as it falls around it.
 Ah, that makes sense. And then the question arises: why does the speed of an object increase when its closer in its elliptical orbit?

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## Why doesn't the moon fall on earth?

Conservation of energy is one way to explain it easily. As the planet comes close to the sun it's gravitational potential energy is lowest so it's kinetic energy is highest.

Mentor
 Quote by ankeshk Ah, that makes sense. And then the question arises: why does the speed of an object increase when its closer in its elliptical orbit?
Simply put, when an the moon is moving towards the earth, it speeds up because of the gravitational pull that is pulling it closer to the earth. Its exactly the same as when you jump off a diving board and accelerate as you fall. Imagine, though, if you jumped off a really tall diving board with enough forward velocity that you'd miss the earth when you fell toward it. That's an eliptical orbit.
 the spped that it travels counter acts the gravity on it. So it doesnt come flying to the earth. :D