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# Confounding Gravity Question

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posted on Jul, 17 2004 @ 10:00 AM
I am not sure how to word this so I'll just explain how I picture it and ask the question.

If I try and build a house on the side of a mountan it will crash to the gound because gravity would pull it down the side of the mountain.

If I build a house on the visible west side of the moon it will stay put because of the moons gravity. If I then move the moon so that it now sits on the earth with say the south pole seated neatly on the earth, would that house now fall and hit the earth?

In other words would the earths gravity negate the moons gravity once they came in contact? Lets pretend like we controlled the contact and it was a soft touch down for the moon upon the earth. no crash..

Or would the moon negate some or all of the earths gravity?

posted on Jul, 17 2004 @ 10:42 AM
I'm not exactly sure what you are trying to explain...but, the Earth's gravity is much more powerful than the moon's because it is bigger than it. The Earth and moon already have conflicting gravity forces, but if the earth and moon "met" and were connected to each other, it would just add more mass to Earth on its orbit, and more gravity I would think....but this question is kind of impossible.

posted on Jul, 17 2004 @ 05:33 PM
The Earth's gravity is about 6 times stronger than the Moon's gravity. If the Moon were placed anywhere on this planet, the Earth's gravity would overcome the Moon's gravity.

Gravity pulls your mass towards a specific location, usually of greatest density. In the Earth's case, this is probably the center of the planet. On the Moon, the same effect would happen. You'd be pulled toward the center of the Moon. However, if you did fall off the side of a mountain it would probably fall too slowly to kill you, unless the fall was so far that you had time to accelerate to terminal velocity. My guess is that it would take about a 30-story fall before you were going fast enough to be killed on impact.

Calculation:
32 ft/(s^2) acceleration rate
120 mi/hr terminal velocity

120 mi/hr * 5280 ft/mi * hr/3600 s = 176 ft/s
32 ft/(s^2) * 1/6 = 5 1/3 or 5.333 ft/(s^2) on the Moon

velocity = acceleration * time
Integrate with respect to time:
displacement = acceration * (time^2)/2

176 ft/s = 5.333 ft/(s^2) * time
time = 33 sec fall until terminal velocity is reached

displacement = 5.333 ft/(s^2) * (33^2)/2 .....(can you find the missing unit)
displacement = 2904 ft

So assuming you were standing still on the mountain and fell, in a 33 second freefall, you'd fall 2904 ft and die. That is a long drop. If you use a traditional story-measurement of 10 feet, you'd have to fall off a 290.4 story building on Mars to die from the fall (on average).

Ok, so my original guess of 30 stories was a bit off. I think you can get the point that the Moon's gravity is nothing in comparison to the Earth's gravity. If you really want to know more, just do a bit of research. Most books don't lie.

[edit on 17-7-2004 by Protector]

posted on Jul, 18 2004 @ 12:14 AM
I think what you are asking is if at the height of the radius of the Moon (1738km) what would be the combined effect of Earth's gravity and the Moon's gravity on an object on the Moon's surface. I don't offhand know of a gravity elevation function, but it is said to be inversely related. (higher up -> less gravity) 6378.137 km = Earth radius; so an object at 6378.137/6378.137 = 1 gravity, (6378.137 + 1738) = 8116.137 ; 6378.137/8116.137 = 0.7858587 * sea level gravity ; Moon's gravity = 0.166667
0.7858587/0.166667 = 4.715151
So the Earth's gravity (down) would still be almost 5 times the Moon's gravity (East) at that elevation. Net effect unless you have steel tie-rods into the Moon's bedrock that house is gonna fall to the surface of the Earth.

WARNING: this could be totally wrong

PS. Im pretty sure even if you could carefully place the Moon on the surface of the Earth with no inertia, the surface tension of the Planet would not be sufficient to hold it back from sinking into the Earth until the two bodies merged into somekind of Earth with a big lump on the side. Eventually it might even completely meld with the Earth into a larger single sphere because the Earth has a molten core.

posted on Jul, 18 2004 @ 12:33 AM
Thats why we need antigravity devices.......... We'lll have a huge antigravity device that is shaped like a golf tee, and without the tee touching the ground, the earth will haveit's own golfball. IT will attract golfers from around the world to go and live, play golf on the moon. Then we will take the moon back up out of orbit and there will be no more golf on TV on Earth.

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