quick gravity question

[modest]

Originally Posted by phillip1882

i realize the moon pulls on the earth with as much force as the earth pulls on the moon. my question deals more with centralfugal force and whether it exists with gravity.

I'm sorry, I misunderstood.

Yes, as others have said, for an object to be in orbit, the force of gravity will be equal to the centrifugal force.

The force of gravity can be calculated:

and the centrifugal force can be calculated:

The force of gravity will equal the centrifugal force:

or,

It might be a fun mental exercise to plug in the numbers which you can get here:
Moon Fact Sheet
and see if this relationship works

Originally Posted by phillip1882

for example, when you simply drop a rock, there is no centralfugal force, or at least i woudn't think there to be, so why would there be centralfugal force with an orbiting body?

Using the equation above, you could calculate the centrifugal force of a rock sitting on the equator. It is spinning around because the earth is spinning - so there is a force associated with a rotating reference frame on the rock. In other words, it is being spun outwards.

However, a rock on the surface is not in orbit. The earth rotates about a thousand miles per hour at the equator which is about a half a kilometer per second. To be in orbit it would need to go 11.2 kilometers per second. Something in orbit then has greater centrifugal force than something sitting on the surface because it has a greater speed. For the rock on the surface the centrifugal force is much less than gravity, so it falls. For a rocket in orbit or the moon in orbit, the centrifugal force is equal to gravity.

Here is a website with more info and a better explanation than mine:

What is centrifugal force?

~modest

[phillip1882]

Originally Posted by KALSTER

...and thus creating a force in the opposite and near equal direction of gravitation, keeping the orbit near stable.

yes this is what im after. though are you certain the force is oppisite and equal to gravity? i would think the force of motion would be perpendicular to gravity. like i said it's unclear to me. it seems to me if there was truly a force oppisite and equal to gravity, then there would be no gravity. of course i'm no physist.

[KALSTER]

Originally Posted by phillip1882

yes this is what im after. though are you certain the force is opposite and equal to gravity? i would think the force of motion would be perpendicular to gravity. like i said it's unclear to me. it seems to me if there was truly a force opposite and equal to gravity, then there would be no gravity. of course i'm no physist.

Yes, the centrifugal force is equal and opposite in the earth-moon system. It is a result of the angular velocity of the body and the force that provides the tension in the rope when you swing a rock tied to a rope in a circular motion. The centrifugal force is the force that provides pseudo-gravity in fictitious rotating space stations. If the force had not been equal, the moon would have fallen onto the earth or it would have drifted off into space.

[Natural]

Originally Posted by phillip1882

yes this is what im after. though are you certain the force is oppisite and equal to gravity? i would think the force of motion would be perpendicular to gravity. like i said it's unclear to me. it seems to me if there was truly a force oppisite and equal to gravity, then there would be no gravity. of course i'm no physist.

I think much of the problem with answering your question is that everyone is assuming that the quantum function of gravity has been explained by modern science. Which it has not. (theories yes... proof no)
In fact there is a whole other set of explanations for the effects of gravity that assumes that gravity is a pushing force instead of a pulling force and that the reason that objects seem to be drawn towards each other is because each object moves in a line which corresponds with the shadowing effect between two objects. In other words each object is "pushed" by gravitons hitting them from all sides except the areas facing each other making one side the "back" (the back being the side opposite the corresponding object), thus pushing them toward each other because of the lack of push on the "front". (in the shadow)
So if you think of something being hit from all sides there would definitely be an "equal and opposite" effect.
Of course this might be thought of as blasphemy by the members of the "Church of Relativity". And if everyone can keep their panties from getting in a twist over that thought, let me reiterate that this is just another theory.
But my point is that there are other theories that work just as well as GR to explain gravity. (some even better and more logical)
Because as I have said before... the problem with the bowling ball on a rubber sheet analogy is that a sheet is 2D and space is 3D. Thus no "surface" to bend. And don't get me started on the fact that space doesn't even actually exist.

[modest]

Originally Posted by Natural

I think much of the problem with answering your question is that everyone is assuming that the quantum function of gravity has been explained by modern science. Which it has not.

1. Phillip's question is perfectly answerable with any theory of gravity. Notice I answered his question perfectly well using Newtonian gravity and the answer would hold true with GR or loop quantum gravity. The answer to his question has nothing at all to do with different theories of gravity, but simple and measurable effects of gravity.
2. No one (not in this thread or in the scientific community) is "assuming that the quantum function of gravity has been explained". That is just plain wrong.

The topic of the rest of your post has recently been discussed in this thread which you might enjoy.

~modest

[Natural]

Originally Posted by modest

1. Phillip's question is perfectly answerable with any theory of gravity. Notice I answered his question perfectly well using Newtonian gravity and the answer would hold true with GR or loop quantum gravity. The answer to his question has nothing at all to do with different theories of gravity, but simple and measurable effects of gravity.
2. No one (not in this thread or in the scientific community) is "assuming that the quantum function of gravity has been explained". That is just plain wrong.

The topic of the rest of your post has recently been discussed in this thread which you might enjoy.

~modest

Right. I wasn't trying to be rude just extremely factual. I was just saying that a real "answer" would be assuming that the answerer had all the facts. And that the facts didn't rely on one of multiple theories. Which would make any answer just another theory and not really an answer.
It's all just a matter of semantics I guess.

[GAHD]

Originally Posted by phillip1882

okay my father and i were disscucing...the moon in orbit around the earth, gravity pulls inward on the moon but does the moon have a pull outward in resistence to that force? i hypothised that no, there is no out ward pull, otherwise the moon would rapidly orbit at a futher and futher distance. my father was on the side of yes, as every force has an oppisite effect, for example with a rock swung on a string, there is an outward pull.

Both observations are right and wrong depending on how you yourself perceive gravity and space.

Originally Posted by phillip1882

i realize the moon pulls on the earth with as much force as the earth pulls on the moon. my question deals more with centralfugal force and whether it exists with gravity...why would there be centralfugal force with an orbiting body?

When dealing with orbital mechanics, there's a few weird ideas. Eg: the moon is orbiting in a straight line that is also a circle. That seems counter intuitive at first but when you think of space as topography, the moon is only moving one direction; forward. Space itself is warped by the earth and moon so that "straight" suddenly becomes relative to a 'Vally' formed by the interference of the two, and the moon just happens to be exactly far enough out that it's Inertia relative to the Vally is enough that it never actually "falls"

The same is also true of the earth, the earth's orbit around the sun looks more like a sign wave than a circle or oval when plotted with the moon in consideration; and the earth is also traveling "straight spiral" around the sun.

Some would explain these lines as Geodesics.

You can use the string in your earlier bola example as an analogy for gravity, but it only goes so far. What might help is if you thought of throwing a rock and how it bends towards the ground; throw it fast enough and by the time it tries to hit the ground, the ground has curved away from it and it just keeps curving...

There is an old mac classic program I had about 15 years ago for orbital simulations that explained things quite well, I'll have a look to see if I can find a new version...no promises though.

[Karnuvap]

Another way to think about orbiting is as follows:
Imagine the Moon going merrily along in a straight line past the Earth.
It will start to fall towards the Earth.
But the Earth is not a huge flat plate (despite what the flat-earthers think) the surface actually curves away (it is spherical).
This curvature is just enough that the path of the moon as it falls means it stays the exact same height above the surface.
So it is constantly falling but the surface of the earth is also 'falling away' so the height remains the same thus the moon stays in orbit.

This might be easier to think about if you imagine firing a bullet horizontally across the ocean. If the speed of the bullet is insufficient it will eventually fall into the ocean. If the speed of the bullet is very high it will shoot off into space. But if the speed of the bullet is just right then the curve that it follows as it falls towards the surface of the ocean is exactly the same as that of the surface of the ocean on our curved planet. Thus it will stay the same height above the ocean (ignoring air resistance).

This high speed example is easier to visualise than the sedate progress of the moon. The further out you are the slower you need to travel.

This explains why the moon is slowly drifting out (contrary to an earlier post) the effect it has on our oceans is slowly sapping energy from the orbit of the moon. Thus it orbits slightly more slowly and thus it orbits slightly further out.

So there is no actual outward force 'generated' by the moon or acting on the moon to counter the pull of the Earth. In fact the moon is blissfully coasting along in what it thinks is free-fall.

Hope this helps.