Why does the moon orbit around the earth?

Question

Please some one answer this b/c my friend and I got into a heated debate about this yesterday, to the point that he bet his iPhone, and i bet $600. He thinks that the earth spinning on it's axis forces a centrifugal force that makes the moon move around the earth. I, on the other hand, think that it is caused sort of like a sling shot as the moon comes closer gravity slings shots it back around us but not enough to escape earths gravity thus bringing it back around us again. Another debate we had was that he thinks we get a full moon when the moon is between the earth and the sun and the light on the moon is caused by a reflection from the earth, whereas I think that a full moon is when the moon is on the opposite side of the earth from the moon and light goes around the earth to hit it!!!!! somebody please help, I think I should get the iPhone, but I need to know the answer first.

Razor, according to the stone and string anology the moon would move in a perfect circle around the earth? I always thought it had an eliptical orbit? Also, is the earth moon model the same for the sun earth model? I understand everyone elses point, and "sling shot" is just a way of expressing how gravity forces the moon to wrap back around the earth, not like it's an actuall sling shot?

Thanks everyone for helping out, as turns out he did fork over the iPhone, but being the good friend I am I gave it back to him. Being able to say I told you so was all the worth it.

Answer 1

Your friend is incorrect. The earth's gravity warps the space around it. The moon is basically moving along in a straight line along the path of least resistance through curved space.

The moon's light is reflected sunlight. The moon is full when the earth is between the moon and the sun, so that the night side of earth sees the moon fully lit up by the sun shining on it.

Answer 2

Your explanation is the more correct of the two.

If the Earth stopped rotating, the moon would continue to orbit with no change at all. A "centrifugal" force is one that pushes to the outside. If such a force existed, it would push the moon away from the Earth. It does not exist. What does exist is a centripetal (towards the center) force. The moon is essentially falling towards the Earth all the time, but has enough sideways velocity that it always misses. That is basically the definition of an orbit, in layman's terms.

A full moon is NOT caused by light reflected from Earth. It is caused by the Earth being ALMOST directly in-between the moon and the Sun. Light from the Sun strikes the moon, and we're in a position to see only the lit half of the moon. I say "almost" because if we were exactly in-between the moon and Sun, the Earth would cast a shadow on the moon. This is known as a lunar eclipse.

Answer 3

Well you are both right... and a little wrong. I think Einstein put it best when he described gravity in a sort of two dimensional way. Think of space as a bed sheet stretched tight on a bed. Now the earth is a large rock placed on the sheet. As the Earth/rock causes the sheet to curve downward, a ball rolled past it is pulled toward the rock. It rolls down the curve and sticks right to it.

Now if you roll the ball at just the right speed it will circle the rock over and over, not falling onto it or rolling away.

And BTW the moons orbit is almost a circle, in
fact thanks to the Apollo missions we know the distance is increasing by a fraction of an inch each 100 years or so.

When the moon is between the Earth and the sun, its called a "New Moon" and you can't see it. The full moon is as you said, when the moon is on the far side of its orbit from the sun.

Don't think thats enough to get you an iPhone, but hope it helps.

Answer 4

Somer,

You are right on both counts, and your friend is wrong. In point of fact, the earth and moon orbit each other. It's just that the earth's mass is so much greater than the moons that the earth only "wobbles" while the moon does a broad circle. The simple reason for the "orbiting" is that the moon is constantly falling towards the earth due to the gravitational attraction between them; they don't collide because the moon is also moving "forward."

Note: Loose Change's answer is more accurate in the post-Einstein age. The earth warps space like a bowling ball on a mattress. The moon moves around this warped space like a marble circling the bowling ball. The notion that one falls toward or is attracted to the other is a bit old-fashioned, but easier to understand.

Full moons occur when the moon is opposite the earth from the sun. The alignment of the earth, moon and sun is rarely in a straight ray, so we just see a beautifully lit full moon. Every now and then they *do* line up perfectly, giving us a "lunar eclipse."

Answer 5

You've mostly figured this out correctly yourself. The Earth is much closer to the Moon than is the Sun, so it has a much stronger gravitational effect. Actually, the Moon DOES orbit the Sun, in a very wobbly line. You could think of it as the Moon orbiting the Sun and then being pushed and pulled by the Earth so that its path is like a sine wave. The expansion of the universe is only relevant on the very largest scales, between galaxies and groups of galaxies. At close range, gravity is much more powerful. This explains why galaxies frequently collide with each other. Even though the universe as a whole is expanding, gravity can pull close galaxies together so that they collide and interact.

Answer 6

on the first question - ur friend is correct. the moon tries to move straight due to its inertia with a certain velocity....whereas, the earth gravity provides the centripetal force to hold it around.
But the gravity is not tht great tht it causes the moon to slam in the earth

think of it as a stone attached to a string and u r rotating it around you....
stone = moon
you = earth
the string = gravity
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as for the seconf question
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you both are wrong.let me giv u an example

put a torch infront of a basketball and take some ball like a baseball........
torch = sun
basketball = earth
baseball = moon

CASE 1 - if u place the ball inb/w the torch and the basketball,the shadow of the baseball will be formed on the basketball - thts a SOLAR ECLIPSE

CASE 2 - if u line up the torch,then the basketball and then the baseball - the shadow of the basketball will fall on the baseball - thts a LUNAR ECLIPSE

CASE 3 - line up the torch and the basketball.and put the baseball on the left or the right.
(to make it more real,stick some small mirror on the baseball)

now the light from the torch will go straight - some of it will fall of the basketball and some of it on the baseball(having a mirror)
the mirror will reflect the light back to dark side of the earth

understood?
u better be cz it took me alot of time to write this:P lol kidding

hope it helps

Answer 7

The reason anything is in orbit is because it is falling towards the object it orbits. His idea of centrifugal force honestly doesn't make sense, and does not explain the moon's orbit.

The full moon is when the moon is "behind" Earth, and light from the sun shines on the moon. New moon is where the moon is between the sun and Earth, and at this phase, indeed, light reflected off the Earth can be seen on the moon.

"... from the moon and light goes around the earth to hit it".
Light travels in a straight path, rather than going "around" the Earth. That is why we cannot see the moon during a lunar eclipse.

Answer 8

because of the earth's gravitational pull the moon is orbiting the earth.

ur right on the full moon thing.
the order is: sun, earth, moon.

Answer 9

You deserve the iPhone as your argument in both the cases are true.

Answer 10

Yeah you do deserve the I phone...you are right...get a text book and prove it to him