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thecosmos123456
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we all know gravity but i was wondering how is it caused ? like in a nebula what causes the particles to come together and form a star or any object in the cosmos
but what causes gravity ,means what causes the particles to come closer to each otherJoe Ciancimino said:The short answer is simply, no one knows, we have no clue as to how gravity works. The closest description of gravity is Einstein's second theory of relativity call The General Theory of Relativity. With this, it is described as mass causing the warping and moment of space itself. It does very well to make very accurate predictions but the actual mechanics are still being debated today. Some insist that space itself is either a tensile fabric or perhaps a fluid, while others insist it must be a force carrier such as the predicted Graviton in particle physics. How does gravity actually work? We really do not know yet.
Science an give you an explanation that tells you how something works, but the ultimate cause of something may never be known. You can always ask, "Well, why does X work the way it does", no matter how deep your explanation goes.thecosmos123456 said:but what causes gravity ,means what causes the particles to come closer to each other
Ravilochana das said:why didn't Earth's gravity pull the moon right to it's surface instead of keeping it in an orbit?
Joe Ciancimino said:The short answer is simply, no one knows, we have no clue as to how gravity works. The closest description of gravity is Einstein's second theory of relativity call The General Theory of Relativity. With this, it is described as mass causing the warping and moment of space itself. It does very well to make very accurate predictions but the actual mechanics are still being debated today. Some insist that space itself is either a tensile fabric or perhaps a fluid, while others insist it must be a force carrier such as the predicted Graviton in particle physics. How does gravity actually work? We really do not know yet.
could it be that the moon is falling through space but the Earth's gravity prevents it from doing so yet it is not strong enough to pull the moon into itself at that distance so gravity then makes it orbit instead?jtbell said:The moon falls (accelerates) toward the Earth at the same rate that an apple would fall if we could hold it stationary at that distance from the Earth and then let it go. The moon doesn't hit the Earth because it's also moving sideways, so it continuously keeps missing the earth. Likewise if you could shoot a cannon ball at the right speed and if there were no air resistance, it would orbit the earth.
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That's a bit harsh, these might not be the words you would choose, but I think it's quite a good description.mfb said:That does not make sense at all. What does "fallingthrough space" and "preventing it from doing so" even mean?
Ravilochana das said:could it be that the moon is falling through space but the Earth's gravity prevents it from doing so yet it is not strong enough to pull the moon into itself at that distance so gravity then makes it orbit instead?
perhaps i should have said traveling through space or going through space or wandering through space. i don't know, isn't traveling through space almost like the same thing as falling through space, not that it has to fall fast or wander fast? If gravity from a planet wasn't holding a moon in orbit wouldn't it just keep on going and going (until something's gravity catches it); If our planet got blown up and somehow or moon wasn't for example. Then wouldn't our moon travel through space almost like it were falling? if you got in a space suit and someone dropped you off somewhere in space do you think you would just remain in one place? I guess things wouldn't be able to fall in the direction we term down too far since they would be caught up in the rotation of the galaxy; but wouldn't that also have to do with gravity? i am just giving a hypothetical description about the behavior the moon would have without the influence of Earth's gravity, or how gravity and this natural traveling if you will, of the moon counteract each other to create an orbit.mfb said:That does not make sense at all. What does "falling through space" and "preventing it from doing so" even mean?
It would be better to say that the moon is obeying Newton's first law: [...] an object that is in motion will not change its velocity unless an external force acts upon itRavilochana das said:the moon is falling through space
It would be better to say that the moon is obeying Newton's second law: [...] the net force applied to a body produces a proportional accelerationRavilochana das said:but the Earth's gravity prevents it from doing so
No, its an ellipse with the Earth at one focus. An oval is a different shape (that is not followed by any object in freefall).Drakkith said:For the Moon, the shape corresponds to an oval, with the Earth at one focus.
MrAnchovy said:No, its an ellipse with the Earth at one focus. An oval is a different shape (that is not followed by any object in freefall).
We don't know how it happens, but it definitely happens. no doubt about that.thecosmos123456 said:we all know gravity but i was wondering how is it caused ? like in a nebula what causes the particles to come together and form a star or any object in the cosmos
Drakkith said:Ellipse! That's the word I couldn't remember!
davenn said:starting to have those "senior moments" Drak ?
I thought Ol' Jim ( see sig.) and I were the only ones with that problem![]()
i seeMrAnchovy said:It would be better to say that the moon is obeying Newton's first law: [...] an object that is in motion will not change its velocity unless an external force acts upon it
It would be better to say that the moon is obeying Newton's second law: [...] the net force applied to a body produces a proportional acceleration
I agree with that except for a few glitches as mentioned by ZapperZ. However, in a parallel thread (off topic there), there is disagreement about how gravitation works.Joe Ciancimino said:The short answer is simply, no one knows, we have no clue as to how gravity works. The closest description of gravity is Einstein's second theory of relativity call The General Theory of Relativity. With this, it is described as mass causing the warping and moment of space itself. [..].
A.T. said:[..] I can just as well say that I'm countering the ground's push on me. Newtons 3rd Law is symmetrical, so this is an arbitrary choice.
I do think that we have more ways of examination than a narrow look at Newton's third law. If the ground was actively pushing up against you, then it would fly upward if you don't stop it. But it doesn't do so. Inversely, without the ground holding you back, you will fall downward.stevendaryl said:[..] the ground is pushing up on you to counteract gravity [..]
harrylin said:I do think that we have more ways of examination than a narrow look at Newton's third law. If the ground was actively pushing up against you, then it would fly upward if you don't stop it. But it doesn't do so. Inversely, without the ground holding you back, you will fall downward.
We agree on that one; it's not the same issue and may cause confusion. However, action and reaction is very standard in physics!stevendaryl said:The distinction between a force that is "actively pushing" and one that is "passively pushing" is not standard in physics, as far as I know. But if you consider the two situations:
In those two cases, there is no distinction in the force the platform exerts on your feet. There is no distinction in the force the rockets exert on the platform. The distinction is in the trajectories, not the nature of the forces.
- You are standing on a platform that is hovering above the Earth's surface, held up by rockets.
- You are standing on a platform that is accelerating through empty space, propelled by rockets.
harrylin said:We fully agree on that one; it's not the same issue.
A firing rocket engine is not the same as the ground; it's not in all aspects the same analysis. The correct way to analyse problems is to work up from simple cases to more complex ones.stevendaryl said:What's not the same issue?
PeterDonis said:[..] [Einstein's] "gravitational field" is not a valid physical cause of anything. [..]
harrylin said:A firing rocket engine is not the same as the ground; it's not in all aspects the same analysis. The correct way to analyse problems is to work up from simple cases to more complex ones.
The movement of the ground is frame dependent. In a free falling frame it is flying upward.harrylin said:If the ground was actively pushing up against you, then it would fly upward...
If the rocket applies the same upwards force to the platform as the ground would (so it hovers), then there is no relevant difference. Both forces result in measurable 1g upwards proper acceleration of the platform.harrylin said:A firing rocket engine is not the same as the ground;
It's partially the same as you say, and the unnecessary complication for the analysis that you introduced - even blurring the analysis of what causes gravity - is that a rocket engine is itself a cause of action while the ground is not a cause of action.stevendaryl said:I don't see a big difference. The ground is held up by pressure forces within the Earth. How is that different than being held up by rockets?
Yes, locally we can pretend that the effect is caused by the upward flying of the ground. However, as we know, the surface of the Earth cannot be flying upward as the radius of the Earth is constant.A.T. said:The movement of the ground is frame dependent. In a free falling frame it is flying upward.
harrylin said:Yes, locally we can pretend that the effect is caused by the upward flying of the ground. However, as we know, the surface of the Earth cannot be flying upward as the radius of the Earth is constant.
Yes, we certainly all agree on that; the point that I made is that it is unhelpful for this discussion, as it does not explain the cause of gravity. It was even the explanation of gravity that was debunked in the other thread; the Earth is not expanding (as it should, to make it work for falling observers from all sides).Drakkith said:I think the point A.T. is making is that from the frame of a free falling observer, it is the Earth that is moving, not them.