quick gravity question

[phillip1882]

okay my father and i were disscucing gravity and we really couldn't come to a consenus as to wheter or not there's an equal and oppsite side to gravity, for example consider 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.

[coldcreation]

Good question.

That's why gravity is called the 'odd-ball' force.

[Moontanman]

Originally Posted by phillip1882

okay my father and i were disscucing gravity and we really couldn't come to a consenus as to wheter or not there's an equal and oppsite side to gravity, for example consider 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.

Yes there is an outward force on the moon, it's called centrifugal force, just like the rock on a string. the moon also pulls the earth toward it, IE the tides. but no there is no opposite force to gravity, gravity is only positive, no anti gravity.

[phillip1882]

well one topic is genneral realtivity, and the other is baisc classical physics. also i wnated to seperate the two because i felt they were both good questions/observations.

[coldcreation]

Originally Posted by phillip1882

well one topic is genneral realtivity, and the other is baisc classical physics. also i wnated to seperate the two because i felt they were both good questions/observations.

If one drops an apple, why does it drop to the ground? Most everyone will respond by saying that the Earth’s gravitational force attracts the apple, and so it falls to the ground. The persons vaguely familiar with GR might answer that the Earth creates a field around it, and like a bowling ball on a rubber sheet, the Earth deforms, ‘stretches,’ the fabric of space causing objects to fall into the Earth’s gravitational potential well. This answer is identical to the first response in that the Earth’s field results in objects being attracted to the Earth. Gravity can accordingly and alternatively be described in at least two ways, both of which are equally justified:

(1) An apple is pulled towards the Earth.
(2) An apple is pushed towards the Earth.

One might argue that it makes no difference. The observation is the same. It’s the same force. Yes true, and the lines of force are pointing in the same direction, but the source is not the same. :O


CC

[Little Bang]

There is a force acting on the moon phillip. The tides actually speed the moon up slightly, hence the moon moves away from the Earth about 1.75 inches every year.

[modest]

Originally Posted by phillip1882

okay my father and i were disscucing gravity and we really couldn't come to a consenus as to wheter or not there's an equal and oppsite side to gravity, for example consider 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.

If you think of gravity as a force (as others have pointed out, this isn't exactly correct) then yes, there is an equal and opposite force.



Here F1 is equal and opposite to F2 either of which can be calculated with newton's equation of gravity there. The force pulling the moon to the earth is equal and opposite the force pulling the earth to the moon.

~modest

[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. 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? there is only left to right motion and the constant pull. or at least that's what i would think.

[KALSTER]

Remember that the moon is basically in freefall. That means there is a constant force between the earth and the moon, as has been described. The moon also has a motion perpendicular to the direction of gravitation. This perpendicular motion is enough for the moon to fall in a near perfect circle around the earth, constantly accelerating (by virtue of constantly changing vector direction) and thus creating a force in the opposite and near equal direction of gravitation, keeping the orbit near stable. I suspect you already know all this and I have been wasting my time.

So whether gravity is purely geometrical or whether it is mediated by a graviton (whose anti-particle would also have positive gravity as result by the way), gravity is always attractive. Centrifugal force and gravity are seperate entities and do not co-exist in any mutual fashion.

[freeztar]

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. 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? there is only left to right motion and the constant pull. or at least that's what i would think.

Good questions Phillip!

It's important to note that centrifugal force is often thought of as a pseudo-force, compared to gravity which is a real force.

See if this helps you:
Centrifugal force - Wikipedia, the free encyclopedia

Also, read the intro to this article.