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a.alexandra
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I understand that the moon doesn't fall down because it is in an orbit around the Earth. Is this orbit created by warped space due to the mass of the earth?
kaiten said:let's do a little though experiment. (let's also ignore air resistance since it should be negligible in space)
first, imagine standing on a hill and dropping a rock. it should fall straight down, no surprises.
now, imagine throwing it forward. it no longer falls straight down, it goes forward and curves down.
now, imagine throwing the rock even faster. the rock goes further. if you keep throwing the rock faster, it keeps going further.
on an infinite, flat world we could do this forever with greater speeds/distances. the earth, however, is curved.
if we zoom out some on our experiment so we can actually see the curvature of the earth, and we continue throwing our rock farther, it starts going farther and farther around the planet.
now, imagine throwing the rock so fast that it goes all the way around the Earth back to you. at this point it should be right where you first threw it and have the same velocity it initially had. that means it will continue around again... and again, and again, and again, etc.
this is essentially what orbit is. the object moves so fast that it falls around the planet.
edit: so, in fact, the moon does fall down, it just has such a huge velocity in a different direction that the direction of the gravitational force on it (and therefore where "down" is) changes really fast as well.
QuarkCharmer said:The velocity of the moon allows it to overcome (well, not completely overcome) the gravitational pull towards the earth. The gravitational pull itself is a centripital acceleration (take a look at any circular motion physics problem). Eventually it will fall into the earth, just like we will eventually fall into the sun. At least, that's my understanding, which could be wrong.
Edit:
A quick google yields that the moon is a few cm further from the Earth each year, indicating that the velocity is exceeding the centripital (gravity), and thus, over time, the moon should leave Earth instead of crashing into it.
a.alexandra said:Thanks!
This makes much more sense now,
Jim1138 said:One could argue that the moon does fall down, it just keeps missing.
Chronos said:Actually, the moon probably can potentially escape Earth orbit, it will just take billions of years longer than for the sun to go red giant. All bets are off when that happens.
Darn! I was about to make that reference myself!:tongue:daveb said:Perhaps we should rename Luna to Arthur Dent?
Chronos said:JPL gives a pedagogical presentation on orbits at http://www2.jpl.nasa.gov/basics/bsf3-4.php. The moon is slowly receeding from Earth due to tidal friction, which is also slowing the rotation of earth.
daveb said:Perhaps we should rename Luna to Arthur Dent?
It is the tidal effects on the solid Earth that have the major effect, not just the effects on the oceans.Velikovsky said:The tidal friction thing is interesting. Would tidal friction not decrease during periods of heavy glaciation? If this were to be the case would the moons regression from Earth not slow down, cease or even reverse? Just a thought.
The moon doesn't fall down because of its constant velocity and the force of gravity between the moon and Earth. The moon's gravity is strong enough to keep it in a stable orbit around Earth, balancing out the pull of gravity towards Earth.
The moon stays in orbit due to the balance between its forward motion and the force of gravity. As the moon moves forward, the gravitational pull from Earth pulls it towards the center, keeping it in a circular orbit.
While it is highly unlikely, there is a very small chance that the moon could fall to Earth due to a collision with another large object or a change in the Earth's gravitational pull. However, this is not expected to happen in the foreseeable future.
The average distance between the moon and Earth is approximately 238,855 miles (384,400 kilometers). However, this distance can vary slightly due to the moon's elliptical orbit around Earth.
Barring any major changes in the Earth's gravitational pull or a collision with another large object, it is believed that the moon will continue to orbit Earth for billions of years. However, as the moon's orbit is slowly expanding, it is possible that it may eventually drift away from Earth and no longer orbit it.