how does the force of gravity from the moon affect the earth?

Answer 1

GREAT QUESTION!

The answer is: In several ways. First of all:

1. Earth rocks!

Instead of following a smooth Keplerian orbit around the Sun, Earth's own centroid performs an oscillatory motion about this "mean path." By careful observations of the nearest PLANETS (but not the Moon --- why not?!) the amplitude of this Moon-induced "rocking" can be measured: Earth's centroid wobbles back and forth by about 3/4 of the Earth's own radius. From this alone, one can deduce that the Moon's mass is ~ 1/80th that of the Earth.

[How?: From cunning arguments, the Greeks worked out long ago that the Moon was about 60 Earth radii distant; but when things are orbiting around one another with an equal but opposite force attracting them, it's the centroid of the COMBINED system that stays fixed, and the sizes of the "orbits" of both objects about their common centroid are inversely proportional to their masses --- just as though there's a giant Archimedes lever out there in space! So that's how the "60" and the "3/4" combine to tell you that M_moon ~ M_earth/80.]

Furthermore, THAT is how it was already known in Victorian times that the gravitational acceleration at the Moon's surface must be ~1/6th that of our familiar 'g' at the Earth's surface.

[The ACTUAL PHYSICAL distance to the Moon is also needed to work this out, so that one can obtain its physical from its angular size. You then plug the Moon's mass and physical size into Newton's Law of Gravity, applied at the Moon's surface. Since the Greeks knew the Moon was ~60 Earth radii away, that actually meant measuring the Earth's size well!

When Newton made his own first "Moon check" on his law of gravity, it didn't seem to fit. He was away home from Cambridge, in Lincolnshire, avoiding the Great Plague of 1666, and thus away from up-to-date books and other information. But some time later, perhaps on returning to Cambridge, he learned of a new measurement of the Earth's size. He then went back to his Moon test again, and found that when he'd corrected his earlier calculation, "it answered pretty nearly."

That's how he first confirmed his Law of Gravity. It tells you something about perseverance.]

So in the end, things like the acceleration at the Moon's surface were already known long before an astronaut demonstrated the "strength" of it by dropping objects on the surface of the Moon, on live television.

2. The tides.

Another effect of the Moon's gravity on the Earth is of course the tides, though this is a more subtle and less direct (scientific) effect, as it's then the DIFFERENTIAL TIDAL FORCES (derived --- chuckle --- from differentiating the Moon's gravitational force at different places all over the Earth/Oceans etc.) that provide the forcing effect. However, as we are riding on the surface of the Earth itself, we can ourselves more directly experience and observe this more subtle effect, through the tides, than we can the "rocking" produced by the stronger, main part of the attraction.

I hope you get to study this some day; it's fascinating stuff!

[Here's a funny thing that has always intrigued students at Starfleet Academy. As viewed in a frame of reference in which the Sun is at rest --- the frame you use when you want to show the planets orbiting the Sun --- what do you think the path of the Moon looks like in space? Does it spiral a lot, in overlapping circuits, around the Earth's path, or does it slowly and majestically make a gradually curving sinusoidal like motion, first curving in, then curving out (relative to the solar direction) about the essentially circular path of the Earth? Would you believe that it always CURVES IN TOWARDS THE SUN?!!

If you know about gravity, acceleration, and the two separate orbital velocites involved (Earth around Sun, Moon around Earth), you can figure this out for yourself. Good luck!]

Live long and prosper.

*** Hey, goring, below. WHAT'S the "Allay anomaly"?! A Yahoo search only shows up nonsensical pseudo-links that can't be opened. Are you even spelling it correctly? BTW: few physicists have heard of Autodynamics; most of those who have think it's simply one of a vast plethora of crackpot "anti-Einstein" relativistic theories.***

Answer 2

Tides are a huge thing. Earth pulls on the moon to keep it in orbit, but the moon pulls on Earth too! It effects the water. Wherever the moon is, there is sort of a bulge in the water (high tide) parallel to it. Perpendicular is low tide. As the moon orbits the Earth and Earth turns, tides change. Now, here's something else: when the moon is aligned with the sun, there are two forces pulling on Earth's water. A very-high tide occurs, or a spring tide. When the moon is perpendicular to the sun, a very-low tide occurs, or an ebb tide. Hope that helps you!

Answer 3

Aside from causing the tides, the moon also stabilizes the earth's rotation so we spin more like a top with our axis of rotation slowly precessing. The other major affect is the slowing of the earth's rotation. The tides caused by the moon resist the earths rotation, slowing it down. Our days used to be 18 hours long eons ago.

Answer 4

There has been theory that related moon pulling the earth. HOwever after the discovery of the Allay anomaly , there is now a doubt about those theories. To completely answer your question would require a very carefull analysis of the Allay anomaly.

Answer 5

For just on thing that is obvious, is the tides of the ocean!