posted 10-27-2001 14:23            

------------------
With proper thrust, pigs fly just fine.
--RFC 1925

posted 10-27-2001 15:55            

*brain explodes*

posted 10-28-2001 11:15            

I think the first obstacle that comes to mind is the lack of a functional gravity shield. Maybe Geordie la Forge can tinker one up, but until we can retain HIS services, we're shit out of luck.

Anyway... a few points here, allowing for the theoretical invention of a gravity shield:

1. No substances that exist in nature possess this property, or it has been heretofore unmeasurable.

2. It is reasonable to assume that any functional 'gravity shield' would require power to operate.

3. Due to the efficiency (or lack thereof) of our technology, it is also reasonable to assume that any generator using a gravity shield wouldn't function, because the draw of the shield would be more than the production of the assembly.

4. For some reason, I think the placement of the shield should be slightly off-center from the bottom, not centered.

posted 10-28-2001 11:22            

If you had the gravity-free zone on half of the diameter of the dumbbell's circle of rotation, all you'd need is bearings which exerted less frictional torque on the dumbbell than the dumbbell itself gained from the conversion of potential energy to kinetic energy on the way from top to bottom position.

It (the dumbbell) also wouldn't have to be mounted as the diameter of the circle, a single-headed one mounted as the radius would work just fine.

posted 10-28-2001 17:56            

As for you, Jimbo: I don't think your analysis of PE explains away the wheel case. In the case of a wheel, a sliver at the bottom has low GPE, a sliver on the left (shielded) side has zero GPE, and a sliver at the top (or just to the right of the top) has high GPE, so there's a constant input of GPE through an infinitesimal rotation. In a more realistic(?) example, assume the gravity shield isn't perfect, assume it only works partially - any two opposing slivers of the wheel still have unbalanced GPE. Analyzing by force, at any point in the wheel's rotation, there's an unbalanced torque driving the rotation, so with frictionless bearings, it should accelerate indefinitely, with KE increasing indefinitely (unless you extract work). An unbalanced weight design makes it more complicated, but still implies that the weight has more energy after each rotation, since it is accelerated in one half of a cycle and not decelerated (as much) in the other.

So in conclusion, it seems like the author is arguing that we can presuppose an arbitrarily efficient gravity shield device, and that this still wouldn't work. The whole Stevin's law thing, to me, looks to be useless since Stevin's law presupposes a closed system, and unbalanced gravity would have the effect of making the system non-closed. No matter how I think about analyzing the matched forces or the PE, it still seems like this would work. Fen, you gonna weigh(heh) in on this?

posted 10-28-2001 18:24            

The wheel is still a wheel, whether or not you magically remove its weight without removing its mass on one side. On the side which DOES have both weight and mass, there is no difference in the sum of potential energy inherent in the wheel no matter how you rotate it: it's a fucking WHEEL. The same mass and weight will be at the exact same point, no matter WHAT point you pick on EITHER edge of the wheel, no matter what position you rotate it to: hence, simply removing its weight while leaving its mass intact on one side will no more cause it to rotate than placing the whole thing in free fall would.

Thought experiment: any given wheel is, due to the simple fact that gravitational field strength is proportional to the cube of the distance, in a stronger gravitational field on one side than the other. If your hypothesis about differing gravitational field strengths on differing sides of wheels causing them to accelerate is true, why don't all wheels accelerate themselves out of control along their axes?

Item:

Your gravity generator IS producing work. This can be demonstrated simply by observing that, in the case of a dumbbell attached at one end to an axis about which it can rotate, the dumbbell has less potential energy at the bottom than it does at the top: yet, if you negate the gravitational field on one side, the dumbbell will GAIN POTENTIAL ENERGY on its unimpeded rise back to the top again.

Where's that energy coming from? It has to come from SOMEWHERE, unless we decide to throw the principle of conservation of mass-energy out the window.

posted 10-28-2001 22:27         

hhhmmmm let me think some more on this

later
Trey

posted 10-28-2001 23:13            

--------------------------------------------
             _______
          /..........\
         /..............\
        /................\
       |..................|
       |....A Ball........|
       |....(of sorts)....|
        \................/
         \............../
           \.........../
             ---------

      +++++++++++++++++++++++++++
-----------------------------------
|   Magnetic Source                 |
-----------------------------------
     (-)(-)(-)(-)(-)(-)(-)(-)(-)(-)

--------------------------------------------

Now... perfectly balanced you would think this would probably keep the ball suspended a short distance above the magnet. It doesnt' though... try it You need several magnets all giving opposing forces on the sides as well. Or a strangely shaped natural magnet.

So... we try something else:

--------------------------------------------
             _______
          /..........\
         /..............\
        /................\
       |..................|
=======|....A Ball........|=======
       |....(of sorts)....|
        \................/
         \............../
           \.........../
             ---------

      +++++++++++++++++++++++++++
-----------------------------------
|   Magnetic Source                 |
-----------------------------------
     (-)(-)(-)(-)(-)(-)(-)(-)(-)(-)

--------------------------------------------

So we give the ball an axle.

But... how do we get the ball to move? HOW? Dammit. Ok... I hear now someone saying "So... dont use a ball".

If you use an object thats unevenly weighted then you end up having to fight a magnetic field as well as work with it. Assuming no friction, no gravity, and a magical line thin magnetic field you could pass the object through... maybe? You know... a lot of so called "perpetual motion" machines you can pick up at your local mall work with strings and magnets... battery powered magnets Find a super-strong natural magnet and you have yourself a fortune.

I find the gravity shield thing much more feasable.

Why dont we look into cold fusion or something instead?

Howcome if I plug my power strip into itself I cant power my computer?
 

posted 10-29-2001 00:01            

I agree with weis- there is an inherent problem other than what Jim suggests. The author doesn't actually say that one need not rely on the gravity shield to prove this wrong, but he certainly implies it. And further:

quote:

---

Originally posted by Jimbo:
...no matter how you rotate it: it's a fucking WHEEL. The same mass and weight will be at the exact same point, no matter WHAT point you pick on EITHER edge of the wheel, no matter what position you rotate it to...

---

quote:

---

Originally posted by Jimbo:
Thought experiment: any given wheel is, due to the simple fact that gravitational field strength is proportional to the cube of the distance, in a stronger gravitational field on one side than the other...

---

quote:

---

Originally posted by Jimbo:
Your gravity generator IS producing work. This can be demonstrated simply by observing that, in the case of a dumbbell attached at one end to an axis about which it can rotate, the dumbbell has less potential energy at the bottom than it does at the top: yet, if you negate the gravitational field on one side, the dumbbell will GAIN POTENTIAL ENERGY on its unimpeded rise back to the top again.

---

There's something tantalizing there, but I haven't got hold of it yet.

posted 10-29-2001 01:11         

only problem is that the point of the machine is to make more or less infinate energy to run things from comps to the lights.

so the only way to make a true perpetual motion machine is to get every ounce of energy it gives off back into it somehow, which is pretty close to impossible.

oh by the way clme, i was working on that cold fusion stuff and i think i figured it out.. only problem is that it'll destroy the universe... so if the universe ends all i got to say is

my bad

hehehe

later
Trey

posted 10-29-2001 04:11            

quote:

---

No, the point is that the mass will be the same, but not the weight.

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Incorrect. No matter what position you rotate the wheel to, if your gravity negation field remains constant, the precise same mass AND weight will be at all given points in space no matter which position you rotate the wheel to - just keep in mind we're talking spatial coordinates, not spots marked on the wheel with magic marker.

The only net effect of placing half a wheel in a gravity negating field would be to lessen the frictional coefficient of its rotation due to relieving half the pressure on the top of the axle. (If you assume real-world components with actual bearings, you'd also do some interesting things to bearing wear patterns over time.)

Stop to consider spatial coordinates plotted along the curve of the wheel - on either side - and ask yourself, what amount of mass, and at what potential energy state, is occupying this coordinate right now? How about if the wheel rotates any given number of degrees? Obviously, assuming a perfect wheel and a stationary axle, the answer will remain the same.

quote:

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You are saying nothing here except that if the gravity shield was not doing work, then the whole system would be a perpetual motion machine. While this is enough to convince me, it is not enough to convince someone who believes in perpetual motion machines.

---

posted 10-29-2001 05:10            

How about if we placed the gravity shield off center? Why does it have to be centered? Would that still have the same effects?

I can (almost) grasp why it wont work with an object of uniform mass, but I'm curious if the same rules apply if only a sliver of the object was under the influence of gravity. Would that be the same dillemma as before, since the mass still be uniform, or does it actually create a change?

How about if I used a gravity generator on a small portion rather than a shield?

-Chris

posted 10-29-2001 06:02            

Again, the important part is that rotating the wheel will not change its potential energy state.

Let's imagine a wheel of uniform mass distribution in a gravitational field. Now let us imagine Chord A, which is an area of space occupying from 0 to 180 degrees of the wheel's arc, and Chord B, which occupies the space 180 to 360 degrees.

The (gravitational) potential energy contained within a volume of space is determined by the mass contained within that space, the distance it could potentially travel through a gravitational field to the stated "ground", and the strength of the gravitational field in question. We can see that, since our rotor is a perfect wheel of uniform mass distribution, the mass contained within either Chord A or Chord B will not change with rotation. The distance to the ground will also not change with rotation, and neither will the gravitational field itself - therefore, the energy state of the rotor remains unchanged at different points of rotation, therefore it will not rotate without outside influence.

The same will be true of the wheel if you arbitrarily remove gravity from Chord B - the potential energy of that Chord will be lowered because the entire mass contained within the chord is now at the same potential energy state it would be if the entire mass occupied a plane at the bottom of the chord, but again, if we're talking about a perfect wheel, rotor position will not produce a change in potential energy.

Now let's examine a different case - let's talk about a rotor which is shaped like a dumbbell. We can arbitrarily assume that Chord A contains ten joules of potential energy when the rotor is at the top of Chord A, and 5 joules of potential energy when the rotor is at the bottom of Chord A. Now we're seeing a change of potential within the same chord based on the position of the rotor - so if the frictional coefficient is low enough, we know that our rotor will, in fact, rotate itself to the position of lowest potential energy.

Now let's imagine we nullify the gravitational field for Chord B of the rotor's travel. We'll start the rotor at the top of Chord A, and ten joules of potential energy - it will drop through the chord, releasing five joules of potential energy, to arrive at the bottom of Chord A - at which point it enters the gravity-free Chord B area. Throughout its period of continued travel (due to inertia, assuming of course a low enough frictional coefficient) through Chord B, the rotor maintains its potential energy state of 5 joules - because even though the height of the rotor changes, the distance through a gravitational field to our stated ground does not. So, this leads us to the rotor reaching the top edge of Chord B and preparing to enter Chord A - as it passes through Chord B to Chord A, it must GAIN five joules of potential energy.

Where did that potential energy come from? Either the "gravity shield", or "pure fucking magic", pick one. Either way, you're having to inject five joules of energy into the system from somewhere.

posted 10-29-2001 07:21            

That is all

posted 10-29-2001 13:21            

Jim's point is this: In order for the apparatus to work, the gravity shield has to interfere with the gravitational effects of a large mass (in this case, earth) on the wheel. If the shield is place dead center, then each static side of the wheel will weigh the same. No motion. If the shield is placed off center, then one side will weigh more than the other, and it will 'fall' continuously, ever faster.

After it blows itself up, you can then build another one with teeth machined into the disk, and blammo! You just built a great engine.

Btw Weis, you'll notice in my original post how I moved from "This is currently impossible" to "here are possible problems" to "here is a problem we have the math and science to describe in principle right now."

Gimme a break. ; )

posted 10-29-2001 16:32            

quote:

---

Originally posted by InThrees:
Jim's point is this:

---

Jimbo- It must be nice to be as sure of things as you are. Forget the first bit of my last message (mass vs weight)- I didn't get your meaning from before.

Now, consider the balance of what I already said. First, forget the wheel, as the author of the page helpfully suggests, and assume an off-balance arrangement. You are still saying
only this: that the shield must do work equal to the potential gained by a mass rising through it in order to be consistent with Energy Conservation. This seems reasonable, but any PMM (or perpetual engine) violates EC- that's the whole point. So I don't see where we disprove PMM by establishing that it violates EC.

Again, the author is very vague. He doesn't phrase this as a formal problem: "You may assume gravity shield is buildable" or "Prove this device will not create energy, even given a perfect non-draining gravity shield"-- but he certainly implies that doing so is possible. And recall, of course, that he knows the answer and we don't.

That said, unfortunately I've had no terrific ideas- only musings about edge effects of the gravity field, of border condition problems from passing in and out of a potential well, and so on.

Still a thinkin' though.

posted 10-29-2001 16:50            

quote:

---

Originally posted by fenomas:
Hee hee... I hate to say it, but that is stupendously not what Jim's point is. Jim's point is that a wheel will NOT turn if it is half in a gravity well

---

Yup. Also not if it's 3/4 in a gravity well, or .005% in a gravity well, or etc. As long as the gravity well itself remains constant, the wheel won't spin.

BUT - here's an interesting thought: if you bring an inert gravity-nullifier within range of the wheel such that its field WOULD cover half the wheel, and then turn it on, the wheel WOULD "bump" once in the direction of rotation away (at the top) from the gravity-nullifier - because the nullifier would have removed the potential energy from the top of the wheel on its side without affecting the potential energy on the bottom.

So it DOES provide torque - but only when it's initially powered on or when it's turned off.

quote:

---

You are still saying only this: that the shield must do work equal to the potential gained by a mass rising through it in order to be consistent with Energy Conservation. This seems reasonable, but any PMM (or perpetual engine) violates EC- that's the whole point. So I don't see where we disprove PMM by establishing that it violates EC.

---

Who said we were? I was expressing a failure to understand why you even have to think about the wheel, or dumbbell, or what have you: if it has frictionless bearings, it's a PMM without need for a gravity nullifier: just give 'er a spin in a perfect vacuum, she'll go forever. If it DOESN'T have frictionless bearings, then it will need a constant input of energy from somewhere - in which case it's no more magical than a combustion engine or a vacuum cleaner.

So I just don't get it - what's special about the combination of the gravity nullifier and the rotor arrangement? Either the nullifier is a PMM by virtue of its ability to unfailingly inject energy all by itself - in which case it's the mystery with or without the rotor - or the nullifier is not a PMM by itself, in which case as soon as the nullifier breaks the whole thing quits moving, and the entire arrangement is no more mysterious than a ferrous rotor with an electromagnet nearby getting cycled on and off.

::shrugs::

So I'll repeat: where's the interest in this thing? I just don't get it. It's like saying "assume an electric motor you don't have to plug into a wall. is it a PMM?"

I did think working out what would happen if you snuck a grav-nullifier up on a rotor and turned it on was pretty neat, though. Now I want one to play with.

posted 10-29-2001 17:38            

Let's say we invent a gravity-nullifier, and we make a portable version that will enclose both itself and a human wearing it on his or her back in a null-grav field. Further assume that there are no half measures - the device cannot ameliorate gravity, only nullify it completely.

If the human puts the null-grav pack on and turns it on without first taking special precautions, he or she is gonna die.

Why? Because contrary to what you might think, if you nullify gravity you won't float gently in place - you'll bob to the surface of the atmosphere like a cork in water.

Buoyant force on a volume is equal to the weight of an equivalent volume of the surrounding medium minus the weight currently contained within the volume - so let's assume a 1m by 1m by 2m rectangular solid for ease of calculation; that's 4 m³. If we assume a 15 degree (Celsius) day with the barometer at 100 kiloPascals (about normal), we're looking at about 1.2kg * 9.81 m/s² of buoyancy per m³, for a total of 47.088 kg-m/s² of buoyant force at sea level.

Great. Now let's further assume that it's me we're talking about, and that I mass 95 kilograms (I do) - by dividing my mass out of the earlier figure in kg-m/s², we can see that I'm going to be accelerated away from the earth at about half a meter per second squared. (This will of course taper off as air pressure and temperature decrease the further we go, but it'll remain relatively constant until well after I've realized how fucking dumb I was not to tie myself to a tether.)

If you do the math, this means I'll be traveling around 11MPH straight up after only ten seconds. Give me a full minute, and I'm doing better than 60MPH.