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\\\"No, I would not agree. We don\\\'t feel any sense of centrifugal force because, in our frame of reference, the earth isn\\\'t moving. It\\\'s the same reason why, when you are flying in an airplane, and the plane is at cruising speed, it feels like the plane is standing still. In your frame of reference, it is.\\\"
In our frame of reference Earth isn\\\'t moving indeed - but in the Sun\\\'s frame of reference, it is. So, an observer on the Sun might ask: \\\'Look at that planet: it\\\'s moving in circles, therefore centrifugal force must be acting on it. Why doesn\\\'t it fly away then?\\\' And the answer would be that it doesn\\\'t fly away because that centrifugal force is canceled out by the force of Sun\\\'s gravity, that\\\'s what\\\'s preventing Earth from flying away. Do you agree with \\\'\\\'that\\\'\\\', that was what I was trying to ask.
Airplane is different - it is a perfectly good inertial frame of reference, no disagreement there, but we are talking about more complicated frames right now.
Your example with a circus performer isn\\\'t exactly what I had in mind; I\\\'ll try to give a better one. Imagine a wheel-shaped [[http://www.daviddarling.info/images/2001_2.jpg space station]] far from Earth. (ever saw \\\'2001\\\'?) It is rotating very quickly, in order to create artificial gravity. People inside the station do not feel motion sickness, or air in their hair, because the air is rotating with them, they don\\\'t feel any motion at all, because they are rotating together with the station, except for one thing: they feel a mysterious force, undistinguishable from gravity, that pushes them towards the walls of the station, away from the axis of rotation. So they wonder: \\\'We are far away from any source of gravity, why is that we are not in the state of weightlessness? What is this strange force which is still causing the apples to fall away from the central axis of the station, when dropped?\\\' And the answer is - centrifugal force, created by rotation. In other words: if you are in space and see stars circling around you, check whether you are in the state of weightlessness or not: if you are not, \\\'\\\'you\\\'\\\' are rotating, if you are - it means that evil alien god Azathoth is messing with the Universe again, rotating it around you. (The second scenario is somewhat less likely.) This is what makes me say that rotation is absolute.
\\\"Also, there can be no absolute rotation because all rotation is, at a certain level, revolution.\\\"
Yes and no. It is unlike the revolution of a planet around the star caused by gravity, and although there is a similarity, it\\\'s not total.
\\\"Furthermore, all revolution is really lateral motion. At any given instant, the molecules in the sphere are moving in a straight line tangential to their revolution. All motion is relative. \\\"
No, they are not. Saying that at any given instant they are moving in a straight line is just as wrong as saying that at every given moment they are standing still, a la Zeno. In reality they are only moving in straight lines +o(something), with some mistake that decreases as the length of arc decreases, but it\\\'s NOT the same as moving in a straight line. This little correction is making the huge difference, all the difference. In fact, you could say that those molecules are \\\'\\\'changing their direction\\\'\\\' at any given moment, that would be closer to truth.
To conclude: I think I was genuinely mistaken about the revolution, thanks for correcting me. But now it seems to me that your other ideas about motion are wrong-wrong, sorry.
In our frame of reference Earth isn\\\'t moving indeed - but in the Sun\\\'s frame of reference, it is. So, an observer on the Sun might ask: \\\'Look at that planet: it\\\'s moving in circles, therefore centrifugal force must be acting on it. Why doesn\\\'t it fly away then?\\\' And the answer would be that it doesn\\\'t fly away because that centrifugal force is canceled out by the force of Sun\\\'s gravity, that\\\'s what\\\'s preventing Earth from flying away. Do you agree with \\\'\\\'that\\\'\\\', that was what I was trying to ask.
Airplane is different - it is a perfectly good inertial frame of reference, no disagreement there, but we are talking about more complicated frames right now.
Your example with a circus performer isn\\\'t exactly what I had in mind; I\\\'ll try to give a better one. Imagine a wheel-shaped [[http://www.daviddarling.info/images/2001_2.jpg space station]] far from Earth. (ever saw \\\'2001\\\'?) It is rotating very quickly, in order to create artificial gravity. People inside the station do not feel motion sickness, or air in their hair, because the air is rotating with them, they don\\\'t feel any motion at all, because they are rotating together with the station, except for one thing: they feel a mysterious force, undistinguishable from gravity, that pushes them towards the walls of the station, away from the axis of rotation. So they wonder: \\\'We are far away from any source of gravity, why is that we are not in the state of weightlessness? What is this strange force which is still causing the apples to fall away from the central axis of the station, when dropped?\\\' And the answer is - centrifugal force, created by rotation. In other words: if you are in space and see stars circling around you, check whether you are in the state of weightlessness or not: if you are not, \\\'\\\'you\\\'\\\' are rotating, if you are - it means that evil alien god Azathoth is messing with the Universe again, rotating it around you. (The second scenario is somewhat less likely.) This is what makes me say that rotation is absolute.
\\\"Also, there can be no absolute rotation because all rotation is, at a certain level, revolution.\\\"
Yes and no. It is unlike the revolution of a planet around the star caused by gravity, and although there is a similarity, it\\\'s not total.
\\\"Furthermore, all revolution is really lateral motion. At any given instant, the molecules in the sphere are moving in a straight line tangential to their revolution. All motion is relative. \\\"
No, they are not. Saying that at any given instant they are moving in a straight line is just as wrong as saying that at every given moment they are standing still, a la Zeno. In reality they are only moving in straight lines +o(something), with some mistake that decreases as the length of arc decreases, but it\\\'s NOT the same as moving in a straight line. This little correction is making the huge difference, all the difference. In fact, you could say that those molecules are \\\'\\\'changing their direction\\\'\\\' at any given moment, that would be closer to truth.
To conclude: I think I was genuinely mistaken about the revolution, thanks for correcting me. But now it seems to me that your other ideas about motion are wrong-wrong, sorry.
