I How does inertia, a property of mass, arise?

[KurtLudwig]

TL;DR Summary

Newton's First law states that an object will continue to move in a straight line or remain at rest. Only when the its velocity is changed, either its speed or its direction, does the property of inertia show itself.

Do todays physicists have a deeper understanding on mass and inertia on how inertia arises?

 

[kuruman]

You skipped the second half of Newton's first law which is "... unless an unbalanced force acts on it." Setting that aside, can you explain what you understand by inertia? I am asking because different people have different understandings of inertia. Also, presumably, you wish to deepen your understanding, so we have to know how deep it is right now.

 

[KurtLudwig]

Inertia shows itself when you hit a pothole on the road, when you make a sudden turn without slowing down, when a tire is mass unbalanced and rotates. Inertia is a property of mass, but it is shows itself only when that mass is being accelerated.

Do physicists have a deeper understanding of inertia now that physicists know about the Higgs field and boson? What causes inertia? I have read about Mach's principle.

I am at the level of an undergraduate in physics and at calculus 3 (vectors and tensors) in mathematics. I first read about the subject on Wikipedia, before asking questions.

Many, many years ago, I worked on inertial guidance systems, with rotating gyros. Later, I dynamically balanced gas turbines and generators. I understand mathematically how unbalances and resonances arise, but not the physics. I can calculate on where to attach a weight or grind off mass to correct dynamic unbalances.

When I read further, physics turns into mathematics: linear algebra, matrices, tensors, differential equations, set theory, and broken symmetries.
Newton's First law was just an observation of a smooth stone sliding on ice. The Greek philosophers could have never observed inertia.

 

[anorlunda]

Aren't you neglecting Newton's 2nd law, f=ma? To change the velocity of an object, to accelerate it in other words, you need a force proportional to the mass.

Your body experience that every time you ride in a car that accelerates or brakes.

Actually, in physics there is something deeper. Newton's laws of motion can be derived from the Principle of Least Action. But that's hardly necessary. Physical laws much match the observations we make in everyday life. Newton did a better job at that than his predecessors. Einstein improved on Newton's Laws when General Relativity extended it beyond everyday life up to universe scale considerations.

 

[kuruman]

Here is an example of how inertia "arises" that is very well understood in terms of Newton's first law. You are driving your car at a constant speed. A book rests on the back seat. You have to veer suddenly and without braking to the left because you almost missed your turn. The book slides across the seat to the right. Why do you think that is?

From what you have said, and this is only a guess, you would view this event as some form of inertia "arising". I view it as a manifestation of the first law: There is an unbalanced friction force between the car's tires and the road to cause it to change its direction of motion to the left. There is an unbalanced friction force between your body and the car seat to cause you to turn to the left. However, the force of friction between the book and the seat is not enough to cause it to turn to the left, so according to the first law it retains its state of motion and keeps going in a straight line. Because you are moving to the left, you interpret the book's behavior as motion away from you to your right. Having had physics, you interpret this behavior as inertia "arising". Does inertia arise? I would say no. The book's state of motion remains the same throughout your decision to change your state of motion. The relatively low force of friction between the book and the seat did not communicate this decision to the book whereas the relatively high force of friction between your body and the seat did.

 

[sandy stone]

Related to the concept of inertia is the idea of conservation of momentum. Physicist Emmy Noether showed that this in turn is a consequence of the fact that the results of experiments do not depend on where they performed. In physics-speak, the invariance of physical laws with respect to translations leads to the conservation of momentum; pretty astonishing when you think about it. Perhaps this is what you're looking for.

 

[Nugatory]

Actually, in physics there is something deeper. Newton's laws of motion can be derived from the Principle of Least Action.

(Anorlunda already knows all this, I'm writing for others reading the thread)

That is indeed true, but it's still just the next turtle (google for "turtles all the way down"). We can use Newton's laws to answer the original question, and then use the principle of least action to explain the origin of Newton's laws... but where does that principle come from? Why should the universe we live in care about it?

We can work our way down through a sequence of ever bigger stronger turtles more powerful and generally applicable laws of physics, but we're always going to end up with something that we accept because observation tells us that that's how the universe works, not because of some deeper explanation.

 

[anorlunda]

I think it was Leonard Susskind who put down the problem of infinite turtles in all circumstances, perhaps tongue in cheek. He was discussing the cosmological principle. He said (my paraphrase):

It's true because it is a principle. Principles are things we observe to never be violated. Principles are not derived from more fundamental things. Other principles that we use include causality and least action.

Of those, I think causality is the strongest. AFAIK, nobody researches what the next turtle under causality might be, we just use the principle to reject any claims that would violate causality.

 

[KurtLudwig]

Thank you for all your answers.

 

[paradisePhysicist]

If you push a block, on a vacuum on ice, it will continue to move based on Newton. But this only applies to solids, if you push a blob of water instead, the water will no longer behave as 1 blob of water but the water behind the water will be traveling faster than the front blobs of the water.

So the cause of Newton behavior is 2 things: the tendency of molecules of a solid object to maintain the same relative distance of neighboring molecules, and 2, the tendency of a molecule to maintain the same speed in space. 2 could be explained by consciousness, if molecules did not maintain the same speed in space then molecules would have either accelerated or decelerated millions of years ago and planets would have never formed, if there were no planets then no consciousness.

 

[Buckethead]

Newton's first law has the problem of turtles all the way down in the part "moves in a straight line" as we are forced to ask "what is a straight line?" A straight line can be defined as what a massive object does when it is "moving" and not being affected by an outside force, but there is your turtle. An object in orbit is not being affected by an outside force and is moving in a "straight line" as per Newton's law, but it is indeed not really a straight line in the traditional sense. Here it might be better to say an object moves in a geodesic unless acted upon by an outside force.

Indeed inertia is one of the greatest mysteries in nature in my opinion.

 

[paradisePhysicist]

Maybe a molecule in orbit, but an object in orbit is subject to multiple forces, example:

 

[trainman2001]

I like the book in the car example. If we were filming the car turning and the book sliding from above, would we then clearly see the book actually continuing in the original direction of travel, i.e., straight ahead? Starts to sound like Einstein to me. Different descriptions of motion depending on the P.O.V. of the observer. Similar to the tossing a ball straight up and down in a passenger car of a moving train, and the "actual" trajectory of that same ball for the observer standing besides the track, seeing the ball following a string of parabolic arcs back to the tossers hand.

 

[Buckethead]

Maybe a molecule in orbit, but an object in orbit is subject to multiple forces, example:

Tidal forces. OK, I'll go with molocule.

 

[paradisePhysicist]

Tidal forces. OK, I'll go with molocule.

Also the wikipedia says this of tidal force: "It arises because the gravitational field exerted on one body by another is not constant across its parts: the nearest side is attracted more strongly than the farthest side. It is this difference that causes a body to get stretched. Thus, the tidal force is also known as the differential force, as well as a secondary effect of the gravitational field. "

I think that is not the full story; while the gravity vector strengths are different in most cases, also the object is subject to stretching, or rather, compressive, forces due to that the directions of the different gravity vectors are at different angles. Example is a space station that matches the Earth's curve exactly:

 

[Ian J Miller]

In my opinion, this is a little like asking why Newton's second law is in that form, or why the equivalence principle is there. I think the short answer is we don't know, we don't know why mass responds to forces in exactly that way but we have equations that tell us what happens, and unless someone has a really bright idea, I am happy to live with that restriction. I know how to calculate, and for the moment, that will have to do.

 

[synch]

[ It is based mainly on gut feeling, but the idea might help discussion ] I think that inertia is not so much a property of mass itself but more a property of the existence of the mass.

 

[Vanadium 50]

What does that even mean? (And why should "gut feeling" matter?)

 

[vanhees71]

I've no clue either. I think "inertia" is just a fundamental property of matter. It's very well observable by everyday experience that you need a large force to accelerate a "bigger" body than a "smaller" one (of the same material). In Newtonian mechanics it's mass which quantifies in concise mathematically feasible fundamental laws what "bigger" or "smaller" in this context of inertia means. There's no explanation given by the natural sciences, why Nature behaves as we observe her. Rather the natural sciences describe how Nature behaves in a quantitative way as far as reproducible objective phenomena are concerned, no more no less.

 

[MikeGomez]

I've no clue either. I think "inertia" is just a fundamental property of matter. It's very well observable by everyday experience that you need a large force to accelerate a "bigger" body than a "smaller" one (of the same material). In Newtonian mechanics it's mass which quantifies in concise mathematically feasible fundamental laws what "bigger" or "smaller" in this context of inertia means. There's no explanation given by the natural sciences, why Nature behaves as we observe her. Rather the natural sciences describe how Nature behaves in a quantitative way as far as reproducible objective phenomena are concerned, no more no less.

I think that inertia is more than "just" a fundamental property of matter.

In the view of General Relativity, an apple does not fall to the ground. The ground accelerates towards the apple, and even though the surface of the planet is accelerating in different directions at different locations, the planet does not grow in size. If I understand correctly, this is explained in GR as the EFE's describe the relationship between mass (energy) and spacetime.

So in my opinion, I think that a better way to say it is that inertia is a fundamental relationship between matter and spacetime.

 

[vanhees71]

GR is a relativistic gauge theory that describes the gravitational interaction, which can be reinterpreted as a dynamical geometric model of spacetime as a Lorentz (or rather Einstein-Cartan) manifold. The apple and the Earth are simply interacting through the gravitational interaction though a fully self-consistent solution of the apple+Earth as a closed two-body system is very difficult (it's already very difficult in the simpler case of electromagnetism). It's of course fully sufficient to describe the spacetime around the Earth and than the motion of the apple around the Earth as a "test particle".

 

[wrobel]

So in my opinion, I think that a better way to say it is that inertia is a fundamental relationship between matter and spacetime.

and what does it practically imply?

 

[wrobel]

There's no explanation given by the natural sciences, why Nature behaves as we observe her. Rather the natural sciences describe how Nature behaves in a quantitative way as far as reproducible objective phenomena are concerned, no more no less.

indeed! physics and metaphysics must be separated with a high and enduring wall

 

[vanhees71]

Metaphysics is something you can turn to as a retired physicist, not before!

 

[jbriggs444]

In the view of General Relativity, an apple does not fall to the ground. The ground accelerates towards the apple, and even though the surface of the planet is accelerating in different directions at different locations, the planet does not grow in size. If I understand correctly, this is explained in GR as the EFE's describe the relationship between mass (energy) and spacetime.

So in my opinion, I think that a better way to say it is that inertia is a fundamental relationship between matter and spacetime.

General relativity is not relevant here. It has nothing to do with inertial mass.

All general relativity accomplishes here is gives you a "place" to sit where objects can be subject to a force and experience a constant proper acceleration without moving outside the lab.

If you have one brick, it takes a support force to hold that brick in place. Two bricks, twice the support force.

If you go far from Earth and climb into a rocket ship that is accelerating at 9.8 m/s² then it takes that same amount of force to support one brick. And still twice as much force to support two bricks.

Nothing to do with curved space-time.

 

[vanhees71]

In relativity what measures inertia is anyway not (only) mass but all kinds of energy and stress, and that's precisely what GR tells us: both the inertial as well as the gravitational meaning mass has in Newtonian physics in relativity is in fact measured by the energy-momentum-stress tensor of "matter and radiation".

Nevertheless GR doesn't tell us in any way, why the phenomena are as they are observed. It only describes them in a much more comprehensive and in some sense imho simpler way than Newtonian mechanics does. In Newtonian mechanics the perfect agreement between all three kinds of mass (inertial, active, and passive gravitational mass) is simply an observation, while in GR it's built in the model from the very beginning (with the above qualification that it's not mass but energy, momentum, and stress).

 

[MikeGomez]

If you go far from Earth and climb into a rocket ship that is accelerating at 9.8 m/s² then it takes that same amount of force to support one brick. And still twice as much force to support two bricks.

Nothing to do with curved space-time.

Clocks tick at a faster rate at the top of the accelerating rocket ship than at the bottom, identically to an equivalent situation on earth. The reason this has nothing to do with curved spacetime is due to the definition of curved spacetime, not the definition of acceleration or inertia.

 

[MikeGomez]

GR is a relativistic gauge theory that describes the gravitational interaction, which can be reinterpreted as a dynamical geometric model of spacetime as a Lorentz (or rather Einstein-Cartan) manifold. The apple and the Earth are simply interacting through the gravitational interaction though a fully self-consistent solution of the apple+Earth as a closed two-body system is very difficult (it's already very difficult in the simpler case of electromagnetism). It's of course fully sufficient to describe the spacetime around the Earth and than the motion of the apple around the Earth as a "test particle".

Right, but he point wasn't about a two body system. It was that the planet is accelerating in all directions at once. Instead of an apple, it could be a dust particle or smaller, or I think at least in principle an infinitesimally small point in spacetime. The surface of the planet still accelerates towards that point.

 

[MikeGomez]

Nevertheless GR doesn't tell us in any way, why the phenomena are as they are observed. It only describes them in a much more comprehensive and in some sense imho simpler way than Newtonian mechanics does. In Newtonian mechanics the perfect agreement between all three kinds of mass (inertial, active, and passive gravitational mass) is simply an observation, while in GR it's built in the model from the very beginning (with the above qualification that it's not mass but energy, momentum, and stress).

Wikipedia states "Although some theorists have speculated that some of these phenomena could be independent of each other, current experiments have found no difference in results regardless of how it is measured:"

I agree that there is very little hope for such speculation. Eotvos performed his experiment 100 years ago, and since then scientists have created increasingly more accurate apparatuses which fail to detect any difference between types of mass.

 

[MikeGomez]

Nevertheless GR doesn't tell us in any way, why the phenomena are as they are observed. It only describes them in a much more comprehensive and in some sense imho simpler way than Newtonian mechanics does. In Newtonian mechanics the perfect agreement between all three kinds of mass (inertial, active, and passive gravitational mass) is simply an observation, while in GR it's built in the model from the very beginning (with the above qualification that it's not mass but energy, momentum, and stress).

You say GR describes the gravitational interaction, but I've read that mathematically "gravity" and "inertia"
enter the EFE's in the same way.

In any case, aside from experimental evidence as well as the mathematics, we also have Einstein's view there is
no difference between gravitation and inertia.

 

[vanhees71]

Indeed, there's no distinction between "gravity" and "inertia" in GR, as far as local physics is concerned, and that's indeed how Einstein discovered it. It's known as the (strong) equivalence principle.

 

[Richard R Richard]

If you push a block, on a vacuum on ice, it will continue to move based on Newton. But this only applies to solids, if you push a blob of water instead, the water will no longer behave as 1 blob of water but the water behind the water will be traveling faster than the front blobs of the water.

At the moment you initiate the interaction,, also in a solid the molecules closest to the point of application will be faster than those further away, after a transitory time, the electromagnetic repulsion forces in the material bonds will maintain the intensity the interaction in the whole mass. If you compare the dimensions of the previous material and during the interaction the dimensions change, it shortens if you push and it stretches if you pull, but the speed at the point of application is always higher than at the rest of the object.

I think that is not the full story; while the gravity vector strengths are different in most cases, also the object is subject to stretching, or rather, compressive, forces due to that the directions of the different gravity vectors are at different angles. Example is a space station that matches the Earth's curve exactly:
Fmass

That is not totally true, for the body of the figure to remain in a stable orbit (circular, elliptical) the centripetal force is equal to the gravitational force, for any portion of mass. You are just neglecting the inertia, due to the change of direction of the velocity, only if you drop with zero velocity at the beginning you will see the approach of the extremes, and it is not due to the change of the module of the acceleration of gravity with the height, but to the change in the direction of the acceleration vector that always points to the center, no matter how dense or massive the object is.
If you rotate two objects of mass #m# joined by an inextensible string in a circular orbit, the string will not lose or gain tension due to the tidal force of the Earth's mass, only with the passage of time it will shorten due to the gravitational attraction of the masses #m# of the objects themselves.

Clocks tick at a faster rate at the top of the accelerating rocket ship than at the bottom, identically to an equivalent situation on earth. The reason this has nothing to do with curved spacetime is due to the definition of curved spacetime, not the definition of acceleration or inertia.

The clocks will then tick faster in the head of a rocket than in the rear engines, while accelerating even in the absence of gravity, so in flat space the clocks are also modified, the variation of the measurement exists only if there is acceleration, regardless whether it is due to propulsion or due to the vertical way in which the ship is arranged in a gravitational field.

I've no clue either. I think "inertia" is just a fundamental property of matter.

Although it is evident in matter, matter is not the only one that experiences inertia, inertia "I think" is related to the change in linear momentum, and photons also have it, solar sails, take advantage of the change in linear momentum of photons , to propel a ship.
A photon reflected in a mirror does not have to have the same energy as the original, if the mirror changes its momentum.
Photons also curve their trajectory under the curvature of space-time.

 

[paradisePhysicist]

At the moment you initiate the interaction,, also in a solid the molecules closest to the point of application will be faster than those further away, after a transitory time, the electromagnetic repulsion forces in the material bonds will maintain the intensity the interaction in the whole mass. If you compare the dimensions of the previous material and during the interaction the dimensions change, it shortens if you push and it stretches if you pull, but the speed at the point of application is always higher than at the rest of the object.

True and correct. Human vision does not detect this, but solids do act non-rigid in this way. The main difference is when you push a liquid, the liquid is not very connected to other parts of the liquid, so some parts of the liquid may end up not moving in the direction you push... whereas in a solid all the parts are connected and will eventually sync up. In our human speed of consciousness this all happens instantly.

That is not totally true, for the body of the figure to remain in a stable orbit (circular, elliptical) the centripetal force is equal to the gravitational force, for any portion of mass. You are just neglecting the inertia, due to the change of direction of the velocity, only if you drop with zero velocity at the beginning you will see the approach of the extremes, and it is not due to the change of the module of the acceleration of gravity with the height, but to the change in the direction of the acceleration vector that always points to the center, no matter how dense or massive the object is.
If you rotate two objects of mass #m# joined by an inextensible string in a circular orbit, the string will not lose or gain tension due to the tidal force of the Earth's mass, only with the passage of time it will shorten due to the gravitational attraction of the masses #m# of the objects themselves.

Centrifugal force does not exist, its a made up force. Imo, centripetal is sort of made up as well. This is quoted from physicsforum.com:

"<sup>4. Centrifugal and Centripetal Forces These are two ways of describing the force on an object associated with its movement in an arc. Centripetal view X “In an inertial frame, the centripetal force is the applied force that makes the object move in an arc.” Centripetal force is a resultant force, not an applied force. ✓ “In an inertial frame, real applied forces have a real resultant force producing all the acceleration. The component normal to the velocity is termed the centripetal force. Arguably, it is better to avoid the term centripetal force altogether and only refer to centripetal acceleration

Source https://www.physicsforums.com/insights/frequently-made-errors-pseudo-resultant-forces/</sup>"

In this case its combining the gravity force with the linear inertia. All the planets are spheres, I assume this has something to do with gravity compressing and bending stuff. As for your string theory, idk I just got up, but later today I will try to run it in the simulation and see what happens.

 

[bhobba]

but where does that principle come from? Why should the universe we live in care about it?

Excellent answer. But at the risk of just being a smartass, it comes from QM. But you are faced with the same issue where does QM come from? The answer is Quantum Field Theory (QFT). That, however, has an interesting twist. Wilson showed using some general assumptions; all theories basically look like QFT at low energy.
https://www.preposterousuniverse.com/blog/2013/06/20/how-quantum-field-theory-becomes-effective/
'Nowadays, we know you can start with just about anything, and at low energies, the effective theory will look renormalizable, which is useful if you want to calculate processes in low-energy physics; disappointing, if you’d like to use low-energy data to learn what is happening at higher energies. Chances are, if you go to energies that are high enough, spacetime itself becomes ill-defined, and you don’t have a quantum field theory at all. But on labs here on Earth, we have no better way to describe how the world works.'

Strange, isn't it.

Thanks
Bill

 

[bob012345]

Think about if there was no property called inertia. We couldn't do anything. Maybe that's why.

 

[paradisePhysicist]

If you rotate two objects of mass #m# joined by an inextensible string in a circular orbit, the string will not lose or gain tension due to the tidal force of the Earth's mass, only with the passage of time it will shorten due to the gravitational attraction of the masses #m# of the objects themselves.

Ran it in the simulations, it just collapses.

Instead of just putting a stationary object, I then put some planets into orbit. The planets orbited for hundreds of years fine without collapsing. Then when I connected the planets together they all just collapsed before one orbit. Maybe the precision isn't precise enough. Maybe a higher precision simulation is needed. In Kerbal do planets automatically have synchronous rotation or are they asynchronous at spawn, then slowly become synchronous over time?

Think about if there was no property called inertia. We couldn't do anything. Maybe that's why.

I thought inertia was the concept of objects in motion staying in motion, or rather, the concept of objects with no motion having no motion, ie. no activity happening.

 

[Richard R Richard]

Instead of just putting a stationary object, I then put some planets into orbit. The planets orbited for hundreds of years fine without collapsing. Then when I connected the planets together they all just collapsed before one orbit. Maybe the precision isn't precise enough. Maybe a higher precision simulation is needed. In Kerbal do planets automatically have synchronous rotation or are they asynchronous at spawn, then slowly become synchronous over time?

First of all I want to thank you for taking the trouble to answer me and publish the animation.
My criticism of this model continues to be that you have not simulated circular rotation, it is inertia, which will keep the "arc of segments" in balance, if you do not introduce movement, I share with you that the mere fact of approaching the center of the Earth is enough for the material to sag.
Or may be I do not understand what you want to demonstrate, the acceleration of two small bodies for hundreds of years in the absence of resistance, will appreciably shorten the distance between them and the rope will buckle as anticipated, the idea is that the collapse occurs almost instantaneously when freeing the extremes, this happens with zero speed but not with speed

$$v_{orbit}=\sqrt{\dfrac{GM}{h+R_E}}$$

 

[paradisePhysicist]

My criticism of this model continues to be that you have not simulated circular rotation, it is inertia, which will keep the "arc of segments" in balance, if you do not introduce movement, I share with you that the mere fact of approaching the center of the Earth is enough for the material to sag.
Or may be I do not understand what you want to demonstrate, the acceleration of two small bodies for hundreds of years in the absence of resistance, will appreciably shorten the distance between them and the rope will buckle as anticipated, the idea is that the collapse occurs almost instantaneously when freeing the extremes, this happens with zero speed but not with speed

$$v_{orbit}=\sqrt{\dfrac{GM}{h+R_E}}$$

The animation only shows a stationary object. I did do a sim with orbit but didn't upload the gif (was sleepy). The stationary object wouldn't stay in orbit so I just made a new sim with planets, the planets orbited for hundreds of years until I connected the planets, then they collapsed into the gravity circle. The Kerbal question was to see what happens when you put a planet with 0 angular momentum into orbit around a bigger planet. Will there be synchronous rotations or will it take a while for the synchronous rotations? One of the reasons the planets collapsed and the strings warped was because the planets did not have synchronous rotations. But the planets collapsed even when I just put a string in the middle and no strings on the outside, which idk could mean the simulation is not precise enough. I thought about it more last night and imagined the space station instead as a bunch of cubes orbiting the earth, at least in my imagination in a perfectly circular orbit, the cubes should, as you said, maintain the same string length between each cube. Except if there are strings on the outside, if there is no synchronous rotations on the cube, then no. So the answer of if a space station experiences any bend would depend on if there are synchronous rotations on cubes inherently or not imo. Also the planets should be called moons but I was sleepy when posting, when I say planets around a big planet this just means moons around a planet.

 

[jbriggs444]

The animation only shows a stationary object. I did do a sim with orbit but didn't upload the gif (was sleepy). The stationary object wouldn't stay in orbit so I just made a new sim with planets, the planets orbited for hundreds of years until I connected the planets, then they collapsed into the gravity circle. The Kerbal question was to see what happens when you put a planet with 0 angular momentum into orbit around a bigger planet. Will there be synchronous rotations or will it take a while for the synchronous rotations? One of the reasons the planets collapsed and the strings warped was because the planets did not have synchronous rotations. But the planets collapsed even when I just put a string in the middle and no strings on the outside, which idk could mean the simulation is not precise enough. I thought about it more last night and imagined the space station instead as a bunch of cubes orbiting the earth, at least in my imagination in a perfectly circular orbit, the cubes should, as you said, maintain the same string length between each cube. Except if there are strings on the outside, if there is no synchronous rotations on the cube, then no. So the answer of if a space station experiences any bend would depend on if there are synchronous rotations on cubes inherently or not imo. Also the planets should be called moons but I was sleepy when posting, when I say planets around a big planet this just means moons around a planet.

It is far from clear what setup(s) are being described here. But it is well known that a rigid ring (e.g. Rimworld) does not orbit in a way that is stable against small perturbations. So it is immediately obvious that a ring of satellites, each tethered to the next with taut strings will not be stable against small perturbations if they are set to moving in an orbit centered on the Earth.

 

[paradisePhysicist]

It is far from clear what setup(s) are being described here. But it is well known that a rigid ring (e.g. Rimworld) does not orbit in a way that is stable against small perturbations. So it is immediately obvious that a ring of satellites, each tethered to the next with taut strings will not be stable against small perturbations if they are set to moving in an orbit centered on the Earth.

In a system with total vacuum, perfect circular orbit and zero particles in space, would the ring of satellites be stable (with no forces besides gravity, the satellite's inertia, and the strings), with just a string in the middle and no outside strings? What about with outside strings?

 

[jbriggs444]

In a system with total vacuum, perfect circular orbit and zero particles in space, would the ring of satellites be stable, with just a string in the middle and no outside strings? What about with outside strings?

I am not sure that I know what you mean by "a string in the middle" or by "outside strings".

One could hazard a guess that "string in the middle" would run a string (e.g. a "beanstalk") from each satellite down to an anchor point at the center of the primary. Such an arrangement would not be stable against small perturbations. Two satellites nudged a bit nearer to one another would gravitate toward each other until they collided.

If, instead, one anchors the beanstalks to the surface of the primary then stability against small perturbations can be achieved. Perturbations away from a vertical angle for a beanstalk will result in a restoring force (if the rotation rate of the primary is high enough and matches the orbital period of the satellites).

 

[paradisePhysicist]

I am not sure that I know what you mean by "a string in the middle" or by "outside strings".

One could hazard a guess that "string in the middle" would run a string (e.g. a "beanstalk") from each satellite down to an anchor point at the center of the primary. Such an arrangement would not be stable against small perturbations. Two satellites nudged a bit nearer to one another would gravitate toward each other until they collided.

If, instead, one anchors the beanstalks to the surface of the primary then stability against small perturbations can be achieved. Perturbations away from a vertical angle for a beanstalk will result in a restoring force (if the rotation rate of the primary is high enough and matches the orbital period of the satellites).

Oh, I don't know what a primary is. String in the middle referred to a string at the center of mass of each satellite connecting it as a link to the others. Outside string is some string which is offset from the center of mass, also forming a linkage to another satellite offset from center of mass.

 

[jbriggs444]

Oh, I don't know what a primary is. String in the middle referred to a string at the center of mass of each satellite connecting it as a link to the others. Outside string is some string which is offset from the center of mass, also forming a linkage to another satellite offset from center of mass.

A "satellite" is an object in orbit around another object. A "primary" is the object about which it orbits.

So the moon is a satellite with the Earth is its primary.
And the Earth is a satellite with the Sun as its primary.

If you have an "outside" string, as I understand your description, we would still have a ring of satellites, each tethered to the next in line. But the attachment point for all of the strings would be somewhere somewhere on the far side of the satellite -- the side facing away from the primary.

That means that each satellite will, if nudged a bit, tend to flip over to the outside of the tether instead of remaining down on the inside.

With strings in the middle, you do not have this sort of instability. But you have a different kind. The problem is that if the ring as a whole remains in a circular arrangement and one side gets a little closer to the primary than the other, the closer side will get closer still and the farther side will get farther away. That is the Ringworld instability difficulty.

 

[synch]

Anything that affects the mass will collapse it's wavefunction which exists from pre-event. Applying a force is not altering the mass, it is altering the existence of the mass. The observed inertia is not from the mass, it is from the previous existence of the mass.

 

[PeterDonis]

Anything that affects the mass will collapse it's wavefunction

First, this is the classical physics forum, not the quantum physics forum; there are no such things as wave functions in classical physics.

Second, even if we were in the quantum physics forum, your claim here is only true on one speculative interpretation of QM (which has been advanced by Penrose and others but which is still speculative), and hence would only be on topic in the QM interpretations forum.

Applying a force is not altering the mass, it is altering the existence of the mass. The observed inertia is not from the mass, it is from the previous existence of the mass.

I don't know where you are getting this part from, but it has nothing to do with Newtonian physics, which is the theory on which this thread's discussion should be based. Personal speculations are off limits here at PF.

 

[synch]

mea culpa ! my apologies..

 

[timmdeeg]

If I understand this correctly B. Haisch attempts to derive the origin of inertia due to the interaction of matter with the quantum vacuum.

https://arxiv.org/abs/physics/9807023
In this ZPF-inertia theory, mass is postulated to be not an intrinsic property of matter but rather a kind of electromagnetic drag force that proves to be acceleration dependent by virtue of the spectral characteristics of the ZPF. The theory proposes that interactions between the ZPF and matter take place at the level of quarks and electrons, hence would account for the mass of a composite neutral particle such as the neutron.

 

[PeterDonis]

If I understand this correctly B. Haisch attempts to derive the origin of inertia due to the interaction of matter with the quantum vacuum.

You have understood the proposed model correctly, yes. That proposal goes back to, IIRC, the 1970s, but has never gotten any traction outside its few proponents. Nor has it made any experimental predictions that are both different from mainstream theories and confirmed by experiment. (Note that the paper you reference is from 1998, and refers to "investigations" currently in progress; to the best of my knowledge, they never panned out.)

 

[Vanadium 50]

That paper was part of an "explanation" of paranormal powers. One of the authors claimed to have them. I would pay it no mind.

 

[timmdeeg]

(Note that the paper you reference is from 1998, and refers to "investigations" currently in progress; to the best of my knowledge, they never panned out.)

Thanks for clarifying that. It seems to confirm that "why" questions don't make too much sense in physics.