studiot Posted November 9, 2022 Posted November 9, 2022 On 11/8/2022 at 3:52 PM, Intoscience said: I'm not taking it as criticism, I appreciate your offer and would be interested in gaining a better understanding. I'm sure I have many misconceptions, which is probably why I struggle to get my head around the models, their relationship and how they fit into the big picture (or small picture). That's good but you didn't answer my question about the model put forward by the OP for discussion. I really don't know why no one seems to want to discuss it. It is quite interesting - though hopelessly incorrect as I have already pointed out - but it does demonstrate action at a distance. The thing about models really needs another thread of its own so I will just say briefly here that a model is basically a copy of some (but not all) aspects of something. Since things - and models are things - can be abstract or concrete that gives four undelying types of model, but it is further complicated by the fact that the model may only indirectly copy the thing. This stems from its old French roots where it meant 'to draw'.
Intoscience Posted November 10, 2022 Posted November 10, 2022 (edited) 12 hours ago, studiot said: That's good but you didn't answer my question about the model put forward by the OP for discussion It's been a long time since I did any study around Newtonian gravity and then it was only very basic stuff, I'm only familiar with this equation So the model presented makes little sense to me, however I'm not qualified enough to comment on it. So I'd be more than happy to be educated further on this subject (math not being my strong point). 16 hours ago, zapatos said: Just to reiterate, remember that none of the models are saying that in "reality" gravity is a force, and none of the models are saying that gravity is in "reality" the result of geodesics. What they are saying is "If you look at it this way, it will explain why we get the results we do...". There are multiple theories on what motivates people. Maslow says people are motivated to meet needs. Skinner says people are motivated by reinforcement. Those are two conflicting ways to look at human motivation. The two models of human motivation conflict because two different people worked out a model of human motivation that successfully predicted behavior. Similarly in the future a person may come up with another model whose description of gravity conflicts with QM and GR. If it turns out that this new model makes better predictions, is easier to use, or is in some other way superior to the existing two, we will then have a third way to describe gravity. Ok, this is probably why I get frustrated. The models basically offer predictions of the behaviour dependent on context. I want to understand the physical properties of gravity (if any) which as being pointed out by others, may not be possible. Thanks 17 hours ago, swansont said: Not sure how that changes things. Newtonian gravity doesn’t have a mechanism. GR has warped spacetime. Quantum gravity would have an exchange of virtual gravitons. How do you test which one is the “true” form? How do we know it’s not invisible pink fairies? Maybe I'm trying to understand gravity fundamentally as a thing rather than as an interaction. Edited November 10, 2022 by Intoscience
studiot Posted November 15, 2022 Posted November 15, 2022 On 11/10/2022 at 7:37 AM, Intoscience said: It's been a long time since I did any study around Newtonian gravity and then it was only very basic stuff, I'm only familiar with this equation So the model presented makes little sense to me, however I'm not qualified enough to comment on it. So I'd be more than happy to be educated further on this subject (math not being my strong point). This really is a difficult and complicated subject to untangle. Not least because Michael McMahon has made some quite perceptive comments as well as posting that flawed diagram. Nor do I see this as belonging in the speculations section. As a straight forward question about Newtonian Physics there is a straight forward answer to his question On 10/27/2022 at 11:48 AM, Michael McMahon said: So does anyone know any symbolic way to elaborate on fictitious forces like the Euler force so as to mimic gravity? Yes indeed that is straight forward but the fictious force required is the radial centrifugal force, not the tangential Euler force. This accounts very well for the easily measurable fact that observed gravity is apparantly weaker at the equator than it is at the pole. The Maths of this used to be on the first year Physics course at London University, I can post it if you wish. However you have entitled this thread Gravity Mysteries and even offered some tantalising comments. which show deeper perception and understanding. On 10/27/2022 at 11:48 AM, Michael McMahon said: So to reconcile gravity as a contact force as opposed to an action at a distance would require an altered viewpoint on multiple forces When forces are first introduced in school Physics, they are defined some along the lines of Quote A force is a push or a pull without being specific about where or how that push/pull is generated. This is the level your diagram is pitched at, but unfortunately it also erroneously shows the normal force displaced from the 'gravity force' forming a couple that should not be present. But the diagram does hide some deeper stuff such as the question How does the adding the box onto the table develop into forces at a distance from the box pressing on the floor under the table legs ? Treating this question requires revisiting the basic force definition and significantly expanding it. You also mention contact forces, another part of the basic treatment, that description needs to be expanded to include th concept of 'body forces' for any sensible discussion. 2
Michael McMahon Posted January 2, 2023 Author Posted January 2, 2023 I've awoken from a dream in which I was floating along the shore and being swept be a stormy wave for me to land over a docking ferry. I saw an oval road system in the lower decks in which the traffic had to be balanced on either side. The surface of the road was tilted inwards around the bends. Perhaps my unconscious mind was elaborating on my Euler theory. What would the effect of uneven tidal heights have on the perceived gravity for passengers driving along the ramps and parking inside the ferry? The uneven depths of the Earth's land crusts are buoyant on the mantle much like the tides of the sea. How do we know this isn't contributing to the downward force of gravity felt on the top surface?
swansont Posted January 2, 2023 Posted January 2, 2023 41 minutes ago, Michael McMahon said: The uneven depths of the Earth's land crusts are buoyant on the mantle much like the tides of the sea. How do we know this isn't contributing to the downward force of gravity felt on the top surface? Uneven mass distribution does contribute, but the effect is small. It’s been measured. https://en.m.wikipedia.org/wiki/Gravity_of_Earth 1
Michael McMahon Posted January 2, 2023 Author Posted January 2, 2023 (edited) 12 hours ago, swansont said: Uneven mass distribution does contribute, but the effect is small. It’s been measured. https://en.m.wikipedia.org/wiki/Gravity_of_Earth Every individual Euler force has a tiny effect on gravity. Yet what if we combined every single Euler factor together from atmospheric pressure to equatorial bulge? Maybe there are so many diverse and invisible Euler forces that when combined would remove the need to view gravity as action at a distance. For example without gravity a person jumping straight up on small boat that's sailing over small waves would mean that their feet would land backwards on a crest or forwards on a descending trough. The boat's surface would accelerate upwards and catch your feet as a little wave would accelerate some parts of the boat more than others. Moreover the rear and front of the boat would overhang the wave at different times. "At latitudes nearer the Equator, the outward centrifugal force produced by Earth's rotation is larger than at polar latitudes. This counteracts the Earth's gravity to a small degree – up to a maximum of 0.3% at the Equator – and reduces the apparent downward acceleration of falling objects... The second major reason for the difference in gravity at different latitudes is that the Earth's equatorial bulge... In combination, the equatorial bulge and the effects of the surface centrifugal force due to rotation mean that sea-level gravity increases from about 9.780 m/s2 at the Equator to about 9.832 m/s2 at the poles, so an object will weigh approximately 0.5% more at the poles than at the Equator." "A person flying at 9,100 m (30,000 ft) above sea level over mountains will feel more gravity than someone at the same elevation but over the sea." "In air or water, objects experience a supporting buoyancy force which reduces the apparent strength of gravity (as measured by an object's weight)." Edited January 2, 2023 by Michael McMahon
Mordred Posted January 2, 2023 Posted January 2, 2023 You can eliminate any issue with action at a distance by applying the mathematics of the Euler Langrangian.
swansont Posted January 2, 2023 Posted January 2, 2023 You keep mentioning Euler force, which is 1) tangential to the rotation, not radial, and 2) dependent on angular acceleration What you haven’t done is quantify anything to demonstrate why this could matter https://en.m.wikipedia.org/wiki/Euler_force
studiot Posted January 2, 2023 Posted January 2, 2023 21 hours ago, Michael McMahon said: I've awoken from a dream in which I was floating along the shore and being swept be a stormy wave for me to land over a docking ferry. I saw an oval road system in the lower decks in which the traffic had to be balanced on either side. The surface of the road was tilted inwards around the bends. Perhaps my unconscious mind was elaborating on my Euler theory. What would the effect of uneven tidal heights have on the perceived gravity for passengers driving along the ramps and parking inside the ferry? The uneven depths of the Earth's land crusts are buoyant on the mantle much like the tides of the sea. How do we know this isn't contributing to the downward force of gravity felt on the top surface? So I was wasting my time offering to discuss your points with you. Thank you and go well.
Michael McMahon Posted February 11, 2023 Author Posted February 11, 2023 On 1/2/2023 at 11:09 PM, studiot said: So I was wasting my time offering to discuss your points with you. Thank you and go well. An object in circular motion that gets released will fly off in a straight line owing to Newton's first law. So an object thrown almost vertically and slightly diagonally upwards from a thin, flat rotating asteroid might appear to be travelling outwards to the edge of the asteroid. This is on account of the fact that the centripetal velocity is faster on the outer edges of an asteroid compared to the interior. As such the faster outer edge will catch up to the thrown object where the object appears to fall to the ground. QED! Someone moving on a circular path cannot infer the straightness of a tangent as they're not standing still. After all a circle and a straight line are perceptually irreconcilable due to the infinite digits of pie. Likewise an object thrown upwards on an asteroid will appear to have a different trajectory between the perspectives of an astronaut on the ground of the asteroid and an astronaut floating in space.
swansont Posted February 11, 2023 Posted February 11, 2023 6 hours ago, Michael McMahon said: An object in circular motion that gets released will fly off in a straight line owing to Newton's first law. So an object thrown almost vertically and slightly diagonally upwards from a thin, flat rotating asteroid might appear to be travelling outwards to the edge of the asteroid. This is on account of the fact that the centripetal velocity is faster on the outer edges of an asteroid compared to the interior. As such the faster outer edge will catch up to the thrown object where the object appears to fall to the ground. QED! Why would it return to the ground if there was no gravity? 6 hours ago, Michael McMahon said: Someone moving on a circular path cannot infer the straightness of a tangent as they're not standing still. After all a circle and a straight line are perceptually irreconcilable due to the infinite digits of pie. Likewise an object thrown upwards on an asteroid will appear to have a different trajectory between the perspectives of an astronaut on the ground of the asteroid and an astronaut floating in space. If you aren’t in an inertial frame, Newton’s laws of motion don’t apply. There is no expectation of an object moving in a straight line.
Michael McMahon Posted February 11, 2023 Author Posted February 11, 2023 (edited) 2 hours ago, swansont said: Why would it return to the ground if there was no gravity? Maybe the relative sideways component of an upward throw would return like a boomerang in such a way the flight path still appeared vertical to someone on the ground of an asteroid. Or just imagine if there was more atmosphere on one side of an asteroid compared to the other where the asteroid rotated faster and slower in semi-circular intervals. Edited February 11, 2023 by Michael McMahon
zapatos Posted February 11, 2023 Posted February 11, 2023 26 minutes ago, Michael McMahon said: Maybe the relative sideways component of an upward throw would return like a boomerang in such a way the flight path still appeared vertical to someone on the ground of an asteroid. Or just imagine if there was more atmosphere on one side of an asteroid compared to the other where the asteroid rotated faster and slower in semi-circular intervals. Is there an atmosphere on asteroids? And one dense enough to impart a boomerang effect?
swansont Posted February 11, 2023 Posted February 11, 2023 26 minutes ago, Michael McMahon said: Maybe the relative sideways component of an upward throw would return like a boomerang in such a way the flight path still appeared vertical to someone on the ground of an asteroid. Or just imagine if there was more atmosphere on one side of an asteroid compared to the other where the asteroid rotated faster and slower in semi-circular intervals. Your straw-clutching is getting more and more contrived.
Michael McMahon Posted February 11, 2023 Author Posted February 11, 2023 1 hour ago, swansont said: Your straw-clutching is getting more and more contrived. We can afford circular styles of argumentation when we're discussing actual circles!
zapatos Posted February 11, 2023 Posted February 11, 2023 Is there an atmosphere on asteroids? And one dense enough to impart a boomerang effect?
swansont Posted February 11, 2023 Posted February 11, 2023 2 hours ago, zapatos said: Is there an atmosphere on asteroids? And one dense enough to impart a boomerang effect? Especially one small enough not to deform into a spherical shape. And one wonders how fast could it rotate without falling apart with such weak gravity.
joigus Posted February 11, 2023 Posted February 11, 2023 12 hours ago, Michael McMahon said: This is on account of the fact that the centripetal velocity is faster on the outer edges of an asteroid compared to the interior. What is a centripetal velocity? You mean angular velocity? Of what? 3 hours ago, Michael McMahon said: Maybe the relative sideways component of an upward throw would return like a boomerang in such a way the flight path still appeared vertical to someone on the ground of an asteroid. Or just imagine if there was more atmosphere on one side of an asteroid compared to the other where the asteroid rotated faster and slower in semi-circular intervals. Please, pick a scenario and stay with it for as long as you can. Reaction of a plane, Euler forces, now atmospheres... These are very different things. What's next? 1 hour ago, Michael McMahon said: We can afford circular styles of argumentation when we're discussing actual circles! I don't see a circular argument. More like a Brownian motion.
MigL Posted February 11, 2023 Posted February 11, 2023 If you have to use 'maybe' and 'if' in your explanation of the effect, you haven't thought it out too well ...
Michael McMahon Posted February 11, 2023 Author Posted February 11, 2023 1 hour ago, zapatos said: Is there an atmosphere on asteroids? And one dense enough to impart a boomerang effect? A comet has a larger atmosphere where buoyancy might mimic a local gravity source for detaching ice: "a celestial object consisting of a nucleus of ice and dust and, when near the sun, a ‘tail’ of gas and dust particles pointing away from the sun." 19 minutes ago, joigus said: More like a Brownian motion. 23 minutes ago, joigus said: What is a centripetal velocity? You mean angular velocity? Of what? An asteroid rotating around the central origin of the asteroid's interior rather than just the asteroid's gradual orbit around the Sun.
swansont Posted February 11, 2023 Posted February 11, 2023 49 minutes ago, Michael McMahon said: A comet has a larger atmosphere where buoyancy might mimic a local gravity source for detaching ice: "a celestial object consisting of a nucleus of ice and dust and, when near the sun, a ‘tail’ of gas and dust particles pointing away from the sun." The tail is caused by the solar wind and radiation pressure. https://skyandtelescope.org/astronomy-resources/why-do-comets-have-tails/ ! Moderator Note This isn’t the WAG forum. Enough is enough. Don’t bring this nonsense up again.
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