[002]
RichardAK
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\\\"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. \\\"
Actually, it is entirely correct to say that, at any given infinitesimally small moment in time, each molecule is moving in a straight line. You are correct to say that they are undergoing a constant centripetal acceleration, which constantly changes their velocities from moment to moment, keeping them moving in a circle. That is what centripetal acceleration 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.\\\"
Yes, in the sun\\\'s frame of reference, the earth is moving. That is completely true. However, a more accurate observation from the sun\\\'s frame of reference would be: \\\'Look at that planet: it is moving in a circle. That means that the direction of its movement must be constantly changing; in fact, when it is on the opposite side of the sun from where it is now, it will be moving in precisely the opposite direction. I know that, since velocity is a vector, any object that is changing its direction of motion must be changing its velocity, meaning it must be accelerating. Ergo, the fact that it doesn\\\'t keep moving in a straight line but instead keeps turning toward the sun must mean that it is undergoing centri\\\'\\\'petal\\\'\\\' acceleration. That is, the sun\\\'s gravity keeps pulling it toward the sun.\\\' It would be incorrect from the sun\\\'s frame of reference to say that the earth is undergoing centri\\\'\\\'fugal\\\'\\\' acceleration. Here is a [[http://www.newton.dep.anl.gov/askasci/phy00/phy00305.htm link to a short piece on the difference between centifugal and centripetal forces]].
I think making an effort to understand the difference would help you understand this whole situation, because then I think you\\\'d understand that saying there\\\'s a centrifugal force depends on being in an accelerating frame of reference in the first place, and that you cannot therefore use centrifugal force to declare one frame more valid than the other.
\\\"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.\\\"
Again, no. The fact that you see the universe spinning around the space station and you do not feel a sense of weightlessness emphatically does not mean that the frame of reference in which the station is spinning and the universe is at rest is more valid than the one in which the station is at rest and the universe is revolving around it. Remember, the reason you feel a sense of artificial gravity due to the station\\\'s rotation is because the station is accelerating relative to you. Just as you get thrown into your seatbelt when the car you\\\'re riding in turns, you are pushed against the side of the station because it is turning. In one frame of reference, you are at rest, and the entire universe, including the station, are revolving around you. As a result, you are at rest and the side of the station gets pushed into you, creating a sense of artificial gravity. In another frame of reference, the universe, including the station, are at rest, and you are accelerating into the side of the station, creating a sense of artificial gravity. In yet another frame of reference, that of a comet or asteroid somewhere, it is at rest, and you, the station, and the rest of the universe are all moving at different velocities. All these frames of reference are equally valid.
Again, if I\\\'m not explaining this well enough, and so far I have failed even to explain the Newtonian concept of centripetal acceleration and how it differs from centrifugal acceleration, I suggest that you consult a professional physicist.
Actually, it is entirely correct to say that, at any given infinitesimally small moment in time, each molecule is moving in a straight line. You are correct to say that they are undergoing a constant centripetal acceleration, which constantly changes their velocities from moment to moment, keeping them moving in a circle. That is what centripetal acceleration 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.\\\"
Yes, in the sun\\\'s frame of reference, the earth is moving. That is completely true. However, a more accurate observation from the sun\\\'s frame of reference would be: \\\'Look at that planet: it is moving in a circle. That means that the direction of its movement must be constantly changing; in fact, when it is on the opposite side of the sun from where it is now, it will be moving in precisely the opposite direction. I know that, since velocity is a vector, any object that is changing its direction of motion must be changing its velocity, meaning it must be accelerating. Ergo, the fact that it doesn\\\'t keep moving in a straight line but instead keeps turning toward the sun must mean that it is undergoing centri\\\'\\\'petal\\\'\\\' acceleration. That is, the sun\\\'s gravity keeps pulling it toward the sun.\\\' It would be incorrect from the sun\\\'s frame of reference to say that the earth is undergoing centri\\\'\\\'fugal\\\'\\\' acceleration. Here is a [[http://www.newton.dep.anl.gov/askasci/phy00/phy00305.htm link to a short piece on the difference between centifugal and centripetal forces]].
I think making an effort to understand the difference would help you understand this whole situation, because then I think you\\\'d understand that saying there\\\'s a centrifugal force depends on being in an accelerating frame of reference in the first place, and that you cannot therefore use centrifugal force to declare one frame more valid than the other.
\\\"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.\\\"
Again, no. The fact that you see the universe spinning around the space station and you do not feel a sense of weightlessness emphatically does not mean that the frame of reference in which the station is spinning and the universe is at rest is more valid than the one in which the station is at rest and the universe is revolving around it. Remember, the reason you feel a sense of artificial gravity due to the station\\\'s rotation is because the station is accelerating relative to you. Just as you get thrown into your seatbelt when the car you\\\'re riding in turns, you are pushed against the side of the station because it is turning. In one frame of reference, you are at rest, and the entire universe, including the station, are revolving around you. As a result, you are at rest and the side of the station gets pushed into you, creating a sense of artificial gravity. In another frame of reference, the universe, including the station, are at rest, and you are accelerating into the side of the station, creating a sense of artificial gravity. In yet another frame of reference, that of a comet or asteroid somewhere, it is at rest, and you, the station, and the rest of the universe are all moving at different velocities. All these frames of reference are equally valid.
Again, if I\\\'m not explaining this well enough, and so far I have failed even to explain the Newtonian concept of centripetal acceleration and how it differs from centrifugal acceleration, I suggest that you consult a professional physicist.
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\\\"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. \\\"
Actually, it is entirely correct to say that, at any given infinitesimally small moment in time, each molecule is moving in a straight line. You are correct to say that they are undergoing a constant centripetal acceleration, which constantly changes their velocities from moment to moment, keeping them moving in a circle. That is what centripetal acceleration 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.\\\"
Yes, in the sun\\\'s frame of reference, the earth is moving. That is completely true. However, a more accurate observation from the sun\\\'s frame of reference would be: \\\'Look at that planet: it is moving in a circle. That means that the direction of its movement must be constantly changing; in fact, when it is on the opposite side of the sun from where it is now, it will be moving in precisely the opposite direction. I know that, since velocity is a vector, any object that is changing its direction of motion must be changing its velocity, meaning it must be accelerating. Ergo, the fact that it doesn\\\'t keep moving in a straight line but instead keeps turning toward the sun must mean that it is undergoing centri\\\'\\\'petal\\\'\\\' acceleration. That is, the sun\\\'s gravity keeps pulling it toward the sun.\\\' It would be incorrect from the sun\\\'s frame of reference to say that the earth is undergoing centri\\\'\\\'fugal\\\'\\\' acceleration. Here is a [[http://www.newton.dep.anl.gov/askasci/phy00/phy00305.htm link to a short piece on the difference between centifugal and centripetal forces]].
I think making an effort to understand the difference would help you understand this whole situation, because then I think you\\\'d understand that saying there\\\'s a centrifugal force depends on being in an accelerating frame of reference in the first place, and that you cannot therefore use centrifugal force to declare one frame more valid than the other.
\\\"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.\\\"
Again, no. The fact that you see the universe spinning around the space station and you do not feel a sense of weightlessness emphatically does not mean that the frame of reference in which the station is spinning and the universe is at rest is more valid than the one in which the station is at rest and the universe is revolving around it. Remember, the reason you feel a sense of artificial gravity due to the station\\\'s rotation is because the station is accelerating relative to you. Just as you get thrown into your seatbelt when the car you\\\'re riding in turns, you are pushed against the side of the station because it is turning. In one frame of reference, you are at rest, and the entire universe, including the station, are revolving around you. As a result, you the side of the station gets pushed into you, creating a sense of artificial gravity. In another frame of reference, the universe, including the station, are at rest, and you are accelerating into the side of the station, creating a sense of artificial gravity. In yet another frame of reference, that of a comet or asteroid somewhere, it is at rest, and you, the station, and the rest of the universe are all moving at different velocities. All these frames of reference are equally valid.
Again, if I\\\'m not explaining this well enough, and so far I have failed even to explain the Newtonian concept of centripetal acceleration and how it differs from centrifugal acceleration, I suggest that you consult a professional physicist.
Actually, it is entirely correct to say that, at any given infinitesimally small moment in time, each molecule is moving in a straight line. You are correct to say that they are undergoing a constant centripetal acceleration, which constantly changes their velocities from moment to moment, keeping them moving in a circle. That is what centripetal acceleration 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.\\\"
Yes, in the sun\\\'s frame of reference, the earth is moving. That is completely true. However, a more accurate observation from the sun\\\'s frame of reference would be: \\\'Look at that planet: it is moving in a circle. That means that the direction of its movement must be constantly changing; in fact, when it is on the opposite side of the sun from where it is now, it will be moving in precisely the opposite direction. I know that, since velocity is a vector, any object that is changing its direction of motion must be changing its velocity, meaning it must be accelerating. Ergo, the fact that it doesn\\\'t keep moving in a straight line but instead keeps turning toward the sun must mean that it is undergoing centri\\\'\\\'petal\\\'\\\' acceleration. That is, the sun\\\'s gravity keeps pulling it toward the sun.\\\' It would be incorrect from the sun\\\'s frame of reference to say that the earth is undergoing centri\\\'\\\'fugal\\\'\\\' acceleration. Here is a [[http://www.newton.dep.anl.gov/askasci/phy00/phy00305.htm link to a short piece on the difference between centifugal and centripetal forces]].
I think making an effort to understand the difference would help you understand this whole situation, because then I think you\\\'d understand that saying there\\\'s a centrifugal force depends on being in an accelerating frame of reference in the first place, and that you cannot therefore use centrifugal force to declare one frame more valid than the other.
\\\"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.\\\"
Again, no. The fact that you see the universe spinning around the space station and you do not feel a sense of weightlessness emphatically does not mean that the frame of reference in which the station is spinning and the universe is at rest is more valid than the one in which the station is at rest and the universe is revolving around it. Remember, the reason you feel a sense of artificial gravity due to the station\\\'s rotation is because the station is accelerating relative to you. Just as you get thrown into your seatbelt when the car you\\\'re riding in turns, you are pushed against the side of the station because it is turning. In one frame of reference, you are at rest, and the entire universe, including the station, are revolving around you. As a result, you the side of the station gets pushed into you, creating a sense of artificial gravity. In another frame of reference, the universe, including the station, are at rest, and you are accelerating into the side of the station, creating a sense of artificial gravity. In yet another frame of reference, that of a comet or asteroid somewhere, it is at rest, and you, the station, and the rest of the universe are all moving at different velocities. All these frames of reference are equally valid.
Again, if I\\\'m not explaining this well enough, and so far I have failed even to explain the Newtonian concept of centripetal acceleration and how it differs from centrifugal acceleration, I suggest that you consult a professional physicist.
