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# Bridge Swing

Long slow sweeps
 (+4) [vote for, against]

With regard to bungee-jumping, at least some bridges seem to qualify as public playgrounds. So, what if we attached a swing (or several) to a bridge? With enough distance from the ground, the swing can be much longer than an ordinary playground swing. See the link for an example location.

The support chains would have to be connected to each other in many places to create the equivalent of a rope ladder, making it relatively safe to descend from the bridge to the swing-seat (and ascend back later). A seat belt might be a good idea.

All by oneself, possibly because of friction in the support chain- links (but see discussion in the annotations), It is possible to sit in a stationary swing and, by moving one's body appropriately, initiate swing- oscillation. I've done that many times as a child.

As the oscillations build in magnitude, the swinger would rush through the air in a very large arc. There are likely to be notice-able/significant G-forces at the bottom of the arc. Be Safe, and Have fun!

 — Vernon, Sep 23 2017

A fairly new bridge with lots of space under it https://www.desertu.../C-FHWA-004-450.jpg
Yes, that is Hoover Dam in the background, which itself is 726 ft (221 m) tall. [Vernon, Sep 23 2017, last modified Sep 26 2017]

As mentioned in an annotation. [Vernon, Sep 25 2017]

How swings actually work http://www.physicsi.../up_in_a_swing.html
[MaxwellBuchanan, Sep 25 2017]

Cut out the seat access and swing start issues thusly https://www.youtube...watch?v=6B68vtWLj2g
[calum, Sep 28 2017]

Unfair sphere swing https://en.wikipedi...Swinging_Pirates.22
As Max said , use arms,feet and whole body to get your heart swinging. [wjt, Sep 28 2017]

Nevis Swing https://live.bungy..../nevis/nevis-swing/
Bridges and swings - no newton however. [mylodon, Sep 29 2017]

 //by moving one's boy appropriately, initiate swing-oscillation// What you get up to in the privacy of your own home is your business.

//All by oneself, because of friction in the support chain- links, It is possible to sit in a stationary swing and, by moving one's bo[d]y appropriately, initiate swing-oscillation. I've done that many times as a child.// Sadly, there are two errors there apart from the typo. (1) Being able to self-start a swing does not depend at all on the friction of the support chain (or rope). (2) As the length of the swing increases, it becomes much more difficult to start, or even maintain, a decent oscillation. This is because the power input comes from you holding the chains (or ropes) and displacing your body relative to them. As the chains get longer, the proportional displacement becomes less, to the point where it's impossible to self-start a significant oscillation. I once made a super-duper swing with ropes about 30ft long from a tall beech tree, and it turned out to be completely useless unless someone was prepared to push the swinger.
 — MaxwellBuchanan, Sep 23 2017

Swimming in the trees again.
 — xenzag, Sep 23 2017

[mb] you could have a gyroscope in a box under the swing, and then have a solenoid try to flip it, causing motion at the swing.
 — beanangel, Sep 23 2017

sorry about the typo --"boy" should indeed have been "body"
 — Vernon, Sep 24 2017

 [MaxwellBuchanan], I can't argue against experiment evidence regarding self-starting, but I still think friction is a relevant factor. On an ordinary stationary swing one first moves one's center of body-mass to an off-plumb position. Without friction involved somewhere that would be impossible to do, thanks to momentum- conservation.

I DID assume one could still do that with a long swing, although I am aware that the ratio of magnitude of off- plumb that one can attain, relative to a long swing, is indeed proportionately much less than the ratio for a short swing. I would expect it to be more difficult to initiate a lasting oscillation, but I didn't expect it to be impossible.
 — Vernon, Sep 24 2017

 //I still think friction is a relevant factor// I'm pretty sure it's not. Many swings have rope suspension, and they work just the same as those with chains; I don't see much friction in either, especially the rope. Likewise, a new chain swing, or one that's just been oiled, works as well as (or better than) an old rusty one where friction would be more.

 The swing works because you push (with your arms) on the rope/chain at hand-height; this displaces the line of the rope/chain relative to your C of M (which, momentarily, stays in the same place because of inertia). Hence, the line of the rope/chain is no longer in a straight line from the suspension point to your C of M, and so movement is induced.

 You also move your lower legs, which causes additional displacement of the CofM.

As for sustaining an oscillation on a long swing - it's not absolutely impossible, but the magnitude is very low. I haven't done either the maths or the quantitative experiment, but it feels as if it's a worse-than-linear relationship (eg, if the swing length doubles, the angle of swing that can be sustained is reduced by much more than 2-fold).
 — MaxwellBuchanan, Sep 24 2017

Although I still think the gyroscope idea would work, you could also put a motor driven rubber paddlewheel extending out, via a long |--------' contraption to under the seat of the swing.
 — beanangel, Sep 24 2017

Rockets. Or a paramotor backpack that only revs to full power on the forward swing - an accelerometer could control that .
 — 8th of 7, Sep 24 2017

 //I still think the gyroscope idea would work//

Not really.
 — MaxwellBuchanan, Sep 24 2017

 //The swing works because you push (with your arms) on the rope/chain at hand-height; this displaces the line of the rope/chain relative to your C of M (which, momentarily, stays in the same place because of inertia).//

 Well, friction does exist in-between rope fibers....

 Are you aware that that what I quoted from you is in- essence the same operating principle of an A.R.T.R.R.? It is possible to displace a center-of-mass more rapidly than the system-as-a-whole can balance-out that displacement, in response to an applied force. But since you are so sure an ARTRR cannot work, it logically follows that your explanation here is nonsensical, and therefore friction must be the answer. Heh, heh, heh.....

In other words, you can't have it both ways. I will accept your explanation of how someone in a stationary swing can initiate the swinging, if you will go back to the ARTRR Idea and pay more attention to the importance of "response times" there.
 — Vernon, Sep 25 2017

 [Vernon], I can assure you that swings do work. I can also assure you that they don't depend on friction, but depend instead on the shifting of one's centre of mass. Swings obey Newton's laws of physics.

The ARTRR also obeys Newton's laws of physics, which is why it doesn't work.
 — MaxwellBuchanan, Sep 25 2017

 [MaxwellBuchanan], you cannot have it both ways. Newton's laws of motion say you CANNOT shift a center-of- mass without affecting something else. A swing and swinger is a single entity. What are you pushing against that allows an initial oscillation to begin? (Air is not dense enough to be a factor here.)

At least an ARTRR makes no bones about having two interacting parts that push against (and pull) each other....
 — Vernon, Sep 25 2017

 //What are you pushing against that allows an initial oscillation to begin? (Air is not dense enough to be a factor here.)// You push against the supporting rope, to shift your centre of mass.

 If you prefer, you can think of it in terms of torques. You lean back with your upper body, and at the same time extend your feet forward. That creates a torque.

If it helps, I've linked a web page explaining how swings work.
 — MaxwellBuchanan, Sep 25 2017

<gedankenexperiment>Not wholly relevant to this problem, but if you were floating in space, at rest, in zero-g with your spacesuit connected to an object with the same mass as yourself 10m away, what would happen if you reched out in front of you and sharply moved the rope connecting you to the mass to one side?</gedankenexperiment>
 — hippo, Sep 25 2017

 //what would happen if you reched out // You might be retching due to the microgravity.

 But I expect you'd get some combination of: (a) The rope being displaced, forming a dog-leg between you and the other mass (b) you and the mass moving toward eachother (c) You rotatating about your vertical axis, opposing the movement of your arm.

I suspect the gedankenexperiment could be made into a realexperiment quite cheaply using an ice rink, a person, a mass, a rope and a tea-tray.
 — MaxwellBuchanan, Sep 25 2017

 //what would happen if you reched out //

 Your helmet would fill up, and you would suffocate.

You and the mass form a closed system. You can pull on the rope and draw the mass towards you. You can then push it away. But you can't change the overalll momentum of the system. You can generate rotation about the centre of mass, but what you can't do is generate displacement, because the energy is all held internally,
 — 8th of 7, Sep 25 2017

//I suspect the gedankenexperiment could be made into a realexperiment quite cheaply// - this is why I'm banned from the local ice-rink...
 — hippo, Sep 25 2017

 // ice rink, a person, a mass, a rope and a tea-tray. //

 If you did it with an ice rink, a person, a plastic drum of carbon disulphide, a length of bungee cord, and a ride-on lawnmower with slick tires, it would probably be more entertaining.



 [hip], the people that run these places have no sense of fun and adventure. They banned us, too ...

</aside>
 — 8th of 7, Sep 25 2017

Dang, Max beat me to the link I was going to post.
 — RayfordSteele, Sep 25 2017

 [MaxwellBuchanan] and {RayfordSteele], the swing link doesn't focus on how a stationary swing can get oscillation initiated. We can deduce some of it by focusing on the partly-imagined triangle created near the bottom of the swing when the swinger pushes or pulls on the chain --but that doesn't really explain how the center-of-mass gets off-plumb. After all, while we are *attempting* to torsion the CoM off-plumb, when creating that triangle, you are also creating a second triangle, from top of swing-chain to hand--hold point to the vertical plumb-line.

I did say that I could accept the claim quoted here: ""(which, momentarily, stays in the same place because of inertia)" --that is, the thing getting "pushed against" to get the CoM off-plumb is the inertia of the system. And the reason I can accept that is because that is how an ARTRR should be able to work (along with additional easily-proved fact that inertia can sometimes be a variable, but that particular factor is not applicable here).
 — Vernon, Sep 26 2017

 //the swing link doesn't focus on how a stationary swing can get oscillation initiated.//

 Well, most people on a swing kick off with their feet to get things started.

 However, it should surely be possible to start from zero. Sit on the swing, and lean back. You can also tuck your legs back under the seat. Now, for a moment, your centre of gravity has moved back, and is behind the swing's seat. But the centre of lift is still the swing's seat. So, the centre of lift is not aligned vertically with the centre of gravity, and so the swing will tend to move forwards.

Perhaps, [Vernon], it would be worth your while conducting a few experiments. The apparatus is relatively straightforward.
 — MaxwellBuchanan, Sep 26 2017

 Yes, he's right. All you need is a tree with a stout side branch, a length of hemp rope, and a chair.

 Tie the rope tightly over the branch, stand on the chair, and knot the rope loosely round you neck.

 Then you can start swinging.

Let us know how it turns out ...
 — 8th of 7, Sep 26 2017

 [MaxwellBuchanan], I remind you of the main text where I (mis)wrote "All by oneself, ..., It is possible to sit in a stationary swing and, by moving one's body appropriately, initiate swing- oscillation. I've done that many times as a child" --and no, I didn't touch the ground during that process.

Which brings us back to the question I asked before (rephrased), "given Conservation of Momentum, how is it possible to move the center-of-mass of swing-and-swinger off-plumb? Are you still going to say that the thing the swinger pushes against is the inertia of the overall system?
 — Vernon, Sep 26 2017

You can get a very tall swing to oscillate without being able to touch ground as long as you are grounded within a gravity-well.
The initial oscillations will be counter-intuitive though because of the length of time it will take the waves to propagate and then return to be amplified.
 — 2 fries shy of a happy meal, Sep 26 2017

 hmm..... if you look at the London Tube system, in between stations the track isn't level, its an inverted parabola or arc or summat. Which means you can basically just let the train fall into the gully then rise again for the next station. Nifty. The investment in energy to start that off is the first vertical fall.

 On a swing... well the CG of the body is at the waist and the pivot of the mechanism as a whole is at the butt, so leaning forward or backwards turns some PE into KE along the arc one way or the other. Likewise the act of bending the knees (in either direction) at the right time moves the rider up a few inches as they travel on the arc of the swing's motion.

 The above would seem to indicate that - swingset aside - you could have a track made from a series of inverted arcs and, sitting on a skateboard starting from the bottom of an arc, move yourself about it : something that could not be done with a straight track.

</ramble>
 — FlyingToaster, Sep 27 2017

 //Are you still going to say that the thing the swinger pushes against is the inertia of the overall system? //

Let me give you a clue. SIt on a swing and don't hold onto the ropes (or hold onto them only at hip-level where they attach to the swing seat). See if you can get the swing swinging.
 — MaxwellBuchanan, Sep 27 2017

 Why does holding the ropes - or not - matter ? There's not enough sticktion in the system to push against.

Easiest though, to look at it from the bleedin' obvious point of view. Even not counting a "cold start", can energy be added to the system solely by the operator's movement ? ie: can you swing higher on the next iteration ? Y/N
 — FlyingToaster, Sep 27 2017

//sticktion// - is that the same as gription?
 — hippo, Sep 27 2017

 okay, "stiction"

(there is actually a "sticktion" that's related but not an exact fit)
 — FlyingToaster, Sep 27 2017

 //Why does holding the ropes - or not - matter ? //

 Well, if you'd ever tried, you'd know it does. I think it's either because (a) it lets you lean back (or forward) and/or (b) it allows you to bend the rope into a dog-leg. However, swings with rigid bars in place of ropes work, so I guess the latter is not essential.

 //can energy be added to the system solely by the operator's movement ? ie: can you swing higher on the next iteration ?// Uh, yes, of course. Have you never actually played on a swing as a child?

Under your own power, you can go from a cold start to a very wide swing. If the swing has ropes/chains, then the limit comes when you go slightly higher than having the ropes horizontal. With rigid supporting bars, you can build up enough momentum to go full circle (Google "Kiiking").
 — MaxwellBuchanan, Sep 27 2017

 //Have you never...// well, yes... your conversation with [V] led me to believe that you hadn't : you could do a cold start with the lower legs only, foregoing gross torso movement. Maintaining one's balance without holding the rope above the hipline isn't related.

The bit I'm getting a kick out of is that - as a child - anytime I wanted to experience 'freefall' like an astronaut, it's just a matter of going to the playground with the tallest swingset.
 — FlyingToaster, Sep 27 2017

self starting... swinging, having fun...finally reaching that long 45 degree arc where two spinning discs (not unlike a ball pitcher) accelerate the swinging up to those adrenaline, rope limping, over 90degree falls.
 — wjt, Sep 28 2017

 [MaxwellBuchanan], you did not answer my question. What do you push against, to get center-of-mass off-plumb, to initiate oscillation of a stationary swing? If it is not friction, as you claimed in an early annotation, then it must be something else, such as the inertia of the system (which you also kind-of mentioned in an early anno).

And you CANNOT have it both ways, claiming that pushing against inertia is OK in some situations, but not OK in others --like how an ARTRR is supposed to work.
 — Vernon, Sep 28 2017

 Why not just swing the bridge? You could have a rickety rope bridge up above in the wind.

Or a resonant near-fail bridge like "galloping gertie" with a swing.
 — beanangel, Sep 28 2017

 //What do you push against, to get center-of-mass off-plumb//

 I thought I covered that. However, if you want further insight, consider the fact that the oscillations of your body are slightly out of phase with the swinging of the swing. Ultimately, that's what makes it all go. It means that you can transfer energy from one oscillator (your body, which is conveniently equipped with muscles) to another (the swing, which isn't).

 In addition, the ability to hold the ropes of the swing, above the seat, is crucial. It means that you can alter the effective length of the pendulum. Without holding the ropes, you can only make the swing wobble back and forth (without a net gain in ampliude), in direct opposition to the movement of your centre of mass.

 I think it is probably fair to say that a swing doesn't break any physical laws.

 I think, in your head, you are getting into a muddle akin to Eric Laithwaite's muddle over gyroscopes - i.e. the interaction of quite mundane physical laws can produce an effect which, looked at the wrong way, appears paradoxical. Eric, alas, only realised his mistake after he had made something a fool of himself, and his career never recovered. Fortunately for you, I assume you don't have a career to lose.

It's a bit like me reeling off a list of huge even numbers and telling you that their sum is an odd number - you can either go through a huge amount of tedious maths to prove me wrong; or you can simply state that even numbers always add up to an even number, then sit back and do something more productive, like drinking. If you wanted to, you could pick over my maths and find my mistake, but what would be the point?
 — MaxwellBuchanan, Sep 28 2017

'Myth Busters' did it with people inside a sphere but unlike a playground or a bridge sized swing there was no enough vector transfer of the people's motion from the inside of the sphere to swing enough.
 — wjt, Sep 28 2017

 //Without holding the ropes, you can only make the swing wobble back and forth (without a net gain in ampliude)// if the movement is synchronous with a natural pendular motion then yes.

I remain (currently) unconvinced that it's impossible, though my muscle-memory assumption may be based on the seat assembly being two wire triangles attached by top apices to the ropes, the bottom sides supporting a plank between them. This would be analgous in some measure to "holding the ropes".
 — FlyingToaster, Sep 29 2017

It would. On the other hand, if the seat has only a single attachment to each rope, it would be hard to balance on it without holding on to the ropes.
 — MaxwellBuchanan, Sep 29 2017

 In zero-g, windmilling one's arms then contracting them to the chest produces a persistent spin. So that would obviously work on an idealized swing set to set up a pendular oscillation.

Of course, full windmilling isn't a normal part of swing operation.
 — FlyingToaster, Sep 29 2017

//windmilling one's arms then contracting them to the chest produces a persistent spin// That's interesting and paradoxical. It must rely on air resistance if it truly imparts a net spin.
 — MaxwellBuchanan, Sep 29 2017

I really love this idea+
 — vfrackis, Sep 29 2017

 mmm...

 A rather short field experiment showed that I don't currently have the balance reflexes to pull it off.

 The basis of the question is then : can a self-powered assemblage, balanced on an horizontal pole (not a seat) on a swing at rest, cause pendulum motion of the CG.

 It's easy enough to see that, using a frictionless horizontal surface instead of a swingset (and substituting horizontal motion for pendulum), the answer is "no".

It's also easy enough to see that if the assemblage is solidly connected, not balanced, the answer is "yes" (that being the "grab the rope" option).
 — FlyingToaster, Sep 29 2017

 // It must rely on air resistance if it truly imparts a net spin. //

 No, it doesn't.

 Consider two contrarotating arms with weights on the end, with a central axle, in vacuo and free fall.

 A motor at the axle rotates the arms.They spin with equal angular velocity. They acquire kinetic energy.

 Now, have springs at the tips of one of the arms push the weights into the axle, and lock the motor.

The system will continue to rotate, because angular momentum is conserved, and the extended arm exerts a disproportionate couple to that of the contracted one.
 — 8th of 7, Sep 29 2017

Yes, but when you return the weights to their starting position, the rotation will be cancelled.
 — MaxwellBuchanan, Sep 29 2017

 [MaxwellBuchanan], you are still not answering the question. I'm talking about the very first maneuver one does while sitting on a stationary swing, to *initiate* oscillation. What do you push against to get your center- of-mass off-plumb?

 We both know you CAN get the CoM off-plumb, because the consequence is an initial small swing-motion, which carries the CoM back toward the plumb-line of verticality (and of course additional properly-timed body-motions can amplify the initial oscillation). The linked swing article explains how to maintain an oscillation (necessary because of things like air resistance), but that is irrelevant to my question above.

Well?
 — Vernon, Sep 30 2017

 [Vernon] From my thoughts, anything, body, legs and probably a nose. A qualifier would be height of pendulum versus how much can be stuck out. Scientific investigation would show the data set. From the Myth Buster's play as the height increases the sphere needed to be exceeded,for a starting oscilation, increases.

PS Technology might be able to fiddle rope structure, through materal science, to decrease limiting sphere.
 — wjt, Sep 30 2017

 This is how a swing starts from rest: The person changes position (moves legs etc). The center of mass stays in the same place, but the position of the "second pivot" will change (where "second pivot" is defined as the location of hands on a rope or the location of the bar on a trapeze). Lets say it moves so that the pivot is slightly behind the the center of mass. The rope is now no longer vertical, so in addition to countering gravity, it is providing a small forward force, accelerating the center of mass forward and accelerating the earth backwards.

Sounds simple, but now consider what happens to the person after they shift positions. Since the "second pivot" is no longer directly above the center of mass, the mass will start to rotate. This becomes a second pendulum. The oscillation period of the second pendulum will be a shorter time because it is shorter length to the center of mass. I'd need to think about this more to be sure, but I suspect that oscillations can be avoided by slow deliberate movements which seemed to work better based on my imperfect memory of childhood experience (though I usually just kicked off from the ground to get started).
 — scad mientist, Sep 30 2017

 [Vernon], it's an interesting question, and I see your point.

 I can't do all the maths and mechanics, but I think it boils down to a couple of factors:

 (1) By shifting your body relative to the swing seat, you can shift the swing seat relative to your body. This means that you don't impart a net movement in the whole system's centre of mass, but you move your body and the swing's seat in opposite directions.

 (2) In order to produce a net gain in amplitude of swing (and a net swing of the total CoM), you clearly need to put energy into the system. I think this energy input comes from pulling (or pushing, alternately) on the ropes, above the swing seat. When you do this, you displace the rope from a straight line into a dog-leg, and that clearly involves applying a force over a distance, which means you're putting energy in.

 So, what I'm saying is that starting the swing involves reciprocal (and balanced) changes in the position of the swing and your body; and increasing the amplitude involves "pumping" the swing's ropes to deliver energy.

Now, this can be tested somewhat. Go find a swing (I'm sure there's one not too far from you). Sit on the seat, but don't hold onto the ropes. If I'm right, swinging your body (or legs) will only introduce a small oscillation in the opposite direction and, if you return your legs/body to their original position, you will be stationary again.
 — MaxwellBuchanan, Sep 30 2017

 Demarcation of 'whole system/centre of mass' under poling out force.

t1 to t2 . The same, I don't think so. Enough of movement to amplify, dependant on the height.
 — wjt, Sep 30 2017

 Under a heavier gravitational pull, the swing should be easier to get the enjoyment started. More muscles are needed, though, but bigger arcs.

The initial wobbles would have to work its way up the rope coping with losses along the way. It's hard to lift from the end, with a lever, a long pipe compared to a shorter one.
 — wjt, Oct 01 2017

 tldr; shift the balance point (seat) out from under the CG, push against the horizontal component of the now non-plumb seat within its arc for net horizontal movement, recover.

 Okay

 Stand on the seat. Start by bending backwards at the waist, which moves the midsection forwards and the head and feet backwards. The CG is still the same, but the balance point (the seat) has now moved backwards, so you'll start falling forwards. Now straighten up again and become a plank. You will continue to fall forwards. The seat will move backwards and upwards along its arc.

 The seat's arc has an horizontal component (which is easiest to visualize with short ropes). Falling pushes against that and introduces a net forwards motion to the body.

 Upon recovery from the fall - bending at the waist the other way to move the seat back underneath the body at the right point and velocity - a net pendular motion will have found to be introduced.

 The fastest way to the greatest pendular motion would involve using the knees and arms as well, and go right through into a mirror movement-sequence for the backswing.

 More difficult (in some respects) to do sitting down, but the same principle.

QESD
 — FlyingToaster, Oct 01 2017

[normzone] briefly considers appropriate "swingers" innuendos, then goes to bed without commenting.
 — normzone, Oct 01 2017

 [gang], keep in mind that *if* the center-of-mass does not move, then it remains exactly under the support-bar for the swing ("in plumb"). Twisting and turning BY ITSELF accomplishes nothing, much like the following two scenarios:

 If you were in zero-G with no ropes, the equivalent challenge is to move your mass from the center of a room toward the edge (but can't do it without action/reaction, most likely by pushing air). If you were in the center of an ice-rink with frictionless skates, there is again the challenge to move your mass somewhere. Twisting and turning all you want gets you nowhere, given Newton's Laws of Motion.

Which brings us back to the swing, where we do have a connection to the outside world (chains or ropes from swing-seat to the support-bar). The swinger is known to interact with THAT to get the center-of-mass off-plumb, and I simply want to know the exact details involved. I suggested in the main text that friction is a factor, and [Max] disagreed, indicating that inertia was a factor. But if he is right, then that means an ARTRR should be able to work, using an equivalent phenomenon....
 — Vernon, Oct 01 2017

 [Vernon] Actually, I think I nailed it 3 posts up from here. ("it" being how to swing without grasping the ropes)

As an interesting sidenote to that : while a flat ice rink can't be navigated, a wavy ice rink can, even starting at rest from the bottom of a wave, with just a single point of (frictionless) contact.
 — FlyingToaster, Oct 01 2017

 [Vernon], did you read my earlier post?

 Here's another maybe simplified version: Sit on the swing, holding the ropes with hands close to shoulders. Rapidly extend your hands straight forward away from your shoulders. Note that the center of mass doesn't move, but the rope in your hands is moved forward. The rope from your hands to the tree branch is no longer vertical so it will be accelerating you backwards as well as countering gravity. Other things like tipping backwards will start to occur in this scenario, but the rearward acceleration through the non-vertical rope is in effect for a non-zero period of time, causing the center of mass of the system to move.

The above doesn't cover the subtleties of ideal motions to get the swing going, but shows a proof of concept of moving the center of mass of a system hanging from a rope with insignificant mass or friction.
 — scad mientist, Oct 01 2017

 Or event simpler: You said //After all, while we are *attempting* to torsion the CoM off-plumb, when creating that triangle, you are also creating a second triangle, from top of swing-chain to hand--hold point to the vertical plumb-line.//

In that second triangle, the chain to hand--hold point is not in line with the vertical plumb line as you said. There is nothing pulling the swing straight up at this point, the chain is pulling at an angle, causing a small front-back acceleration of the mass.
 — scad mientist, Oct 01 2017

 [Vernon], I think most of us agree that:

 (a) swings work by physics

 (b) the details of the physics are subtle and interesting, but only in the same way that Eric Laithwaite's gyroscope stuff was interesting (ie, the application of known physics can sometimes yield counterintuitive results; but no new physics is required).

 (c) friction (in the rope/chain) is unlikely to be a factor - rope swings work better than rusty chain swings, for instance, yet the former have negligible friction. Air resistance is also likely to be a hindrance rather than a help.

 (d) The energy input comes from the swinger's muscles, either by accelerating parts of the body to and fro in time with the swing; and/or by pulling on and bending the ropes (thereby lifting the swinger against gravity).

 Regarding ARTRR, I don't believe it works, for the same reason that I don't believe a complicated system of weights, magnets and wheels will deliver perpetual motion: if it breaks such a basic law of physics, then I don't need to waste time picking over endless details.

 Also, your ARTRR as described is quite simple and, if it worked, would guarantee you a Nobel prize as well as fame and fortune. The fact that you have made absolutely zero progress in demonstrating it in the thirteen YEARS since posting it is quite a strong indication that doesn't work. However, if you really are still short of the hundred dollars needed to test ARTRR, let me know and I will (really and truly) transfer you the money immediately.

In this house, we obey the laws of thermodynamics.
 — MaxwellBuchanan, Oct 01 2017

 //As the oscillations build in magnitude//

That could be a problem with equal and opposite forces. You'd get an increasingly large perpendicular force on the bridge which may start an oscillation in the bridge itself. The traditional fix is to attach four 1n4148 diodes near the swing, in a 'bridge rectifier' circuit.
 — bigsleep, Oct 01 2017

 [scad mientist], you are talking about pushing against the inertia of the system. I have no problem with that.

 [MaxwellBuchanan], you are making the erroneous assumption that someone cannot spend years living paycheck-to-paycheck, and thus not have the funds needed to spend on anything but necessities.

PLUS you are making the unwarranted assumption that we know all the laws of physics, when obviously we don't. Otherwise there would not be a 120-orders-of-magnitude discrepancy between QM and GR. (And one way to resolve that discrepancy leads to the conclusion that momentum can exist in a radiant form.)
 — Vernon, Oct 03 2017

The primary difference between this and the fARTRR is that a swing is an oscillating/rotating system; it has an external point of support.
Your fARTRR is susposed to work linearly, lacking that "external" connection that allows useful things like resonance.

 [neutrinos shadow], you missed the point. A swing and its support-chains (or ropes), which constitute the move-able part of an overall swing "sytem", has inertia, and the swinger pushes against that inertia to slightly move the center-of-mass of the move-able part of the system. Therefore the connection between the move-able part and the immovable part of the system is irrelevant.

 In an ARTRR, there is one additional factor, which is that the inertia of each part of the overall system can change. So if Part A has more inertia than Part B, then when a force is applied to both parts, Part B moves before Part A. Then the system is altered such that Part A will have less inertia that Part B, and now when force is applied to both parts, Part A can move before Part B. The proper geometric configuration of the system is supposed to lead to both parts moving in the same direction.

 [MaxwellBuchanan], in another Idea somewhere recently posted, I mentioned that anti-matter cannot have negative mass and be gravitationally repelled, due to E=MC2 --the positive energy specified in that equation can only yield positive mass, for both matter and anti- matter.

 Negative mass will be associated with both negative energy and a negative value of Planck's Constant. There is no other way to mathematically describe Uncertain fluctuations in the vacuum, below the "zero" mark (which can in turn be associated with negative-mass virtual particles).

 If half of all the virtual particles in the vacuum have negative mass, then the 120 orders-of-magnitude inconsistency between QM and GR disappears easily. But pairs of negative-mass virtual-particles can only become real particles if they can absorb some real negative energy, and so far as we know, none is available. The Uncertainty Principle allows a *temporary* violation of Energy Conservation, but nothing more than that.

 Now consider something else. I also mentioned the possibility of pairs of virtual particles appearing, one of which has positive mass and the other has negative mass. If the particles are equal and opposite, ZERO energy is needed for both to appear. BUT, look: (+m)(+v)<-- poof! -->(-m)(-v) The total momentum is non-zero, when such a virtual pair pops into existence. Well, remember that Heisenberg's original formulation of the Uncertainty Principle associated momentum with position. We can have a temporary violation of Momentum Conservation just as we can have a temporary violation of Energy Conservation (per different Uncertainty formulation).

 LOGICALLY, if such a pair of virtual particles could manifest long-term, then it is essential that they absorb some Real Momentum (just like "ordinary" virtual-particle pairs need to absorb Real Energy to exist long-term).

Well, we are talking about totally pure Momentum there, entirely dissociated with ordinary mass or energy. And so I repeat what I previously wrote, that one possible solution to the huge existing discrepancy between QM and GR leads us straight to the idea that momentum can exist in a pure (possibly radiant) form. The ARTRR is theoretically another way to generate that kind of momentum, and thus would not violate Momentum Conservation.
 — Vernon, Oct 04 2017

point of contention : the swingseat and ropes have no inertia of any importance.
 — FlyingToaster, Oct 04 2017

[Vernon],[Vernon], [Vernon]. I enjoyed your last anno, but did not have time to embark on the long voyage of reading it. Perhaps, to save time, you could borrow a length of rope and a bridge and report back.
 — MaxwellBuchanan, Oct 04 2017

{MaxwellBuchanan], the first 2 paragraphs of that anno were not directed to you, so skipping them is fine. The next 3 paragraphs of that anno are mostly about something I previously pointed out in another message, so skimming them is fine (just to refresh memory). Only the last 3 paragraphs of the anno, not such a vast amount of material, needed "new" attention from you.
 — Vernon, Oct 04 2017

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