Perpetual motion machine examination rules, please.

[petre]

and a dictionary is a physics book in what language?
Gravity (on earth)=9.81 m/sec^2=32.2 ft/sec^2=386.1 in/sec^2. Those values, folks, are accelerations. Now you can get into semantics all you want, but the force is a result of an acceleration acting on a mass. The entire purpose of physics and such is to model an accurate approximation of reality. Treat gravity as an acceleration and you do that. Treat it as a force, and you can go astray easily.
Weight is a force. think of it this way: A force can be measured. Put a scale on the side of a 100 lb box, and push it with a 10 lb force. Then put the same scale on a 1 lb box and (try to) push it with a 10 lb force. Big difference in reactions, huh?
If gravity were a force, the value of weight would be constant, and we would all weigh the same.

Since you have declined the offer to quote a source first, I will now take the opportunity. To be fair, I resolved to do a simple google on "Gravity" and post the information found there. Here it is:

http://csep10.phys.utk.edu/astr161/lect/history/newtongrav.html

Probably the more correct version of the story is that Newton, upon observing an apple fall from a tree, began to think along the following lines: The apple is accelerated, since its velocity changes from zero as it is hanging on the tree and moves toward the ground. Thus, by Newton's 2nd Law there must be a force that acts on the apple to cause this acceleration. Let's call this force "gravity", and the associated acceleration the "accleration due to gravity". Then imagine the apple tree is twice as high. Again, we expect the apple to be accelerated toward the ground, so this suggests that this force that we call gravity reaches to the top of the tallest apple tree.

I then do a google on "Gravity is not a force" and the first link I get is:

http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html

In the simple Newtonian model, gravity propagates instantaneously: the force exerted by a massive object points directly toward that object's present position. For example, even though the Sun is 500 light seconds from the Earth, Newtonian gravity describes a force on Earth directed towards the Sun's position "now," not its position 500 seconds ago. Putting a "light travel delay" (technically called "retardation") into Newtonian gravity would make orbits unstable, leading to predictions that clearly contradict Solar System observations.

In general relativity, on the other hand, gravity propagates at the speed of light; that is, the motion of a massive object creates a distortion in the curvature of spacetime that moves outward at light speed. This might seem to contradict the Solar System observations described above, but remember that general relativity is conceptually very different from Newtonian gravity, so a direct comparison is not so simple. Strictly speaking, gravity is not a "force" in general relativity, and a description in terms of speed and direction can be tricky.

So I now suggest that in the Newtonian model, Gravity is a force. In Einstein's relativity model, Gravity is an acceleration. That's only partially right though, since relativity further points out that it's not really acceleration, it's the bending of space to make it look like the object is accelerating, but really it is just obeying its own inertia in the new bent space.

 

[rwguinn]

Since you have declined the offer to quote a source first, I will now take the opportunity. To be fair, I resolved to do a simple google on "Gravity" and post the information found there. Here it is:

http://csep10.phys.utk.edu/astr161/lect/history/newtongrav.html



I then do a google on "Gravity is not a force" and the first link I get is:

http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html



So I now suggest that in the Newtonian model, Gravity is a force. In Einstein's relativity model, Gravity is an acceleration. That's only partially right though, since relativity further points out that it's not really acceleration, it's the bending of space to make it look like the object is accelerating, but really it is just obeying its own inertia in the new bent space.

Again, I suggest that we are quibbling over semantics. Let's talk mathematically. Words have meaning, but that meaning can be twisted and skewed.
The equations for motion of an object are:
X=.5*x''*m*t^2 + x'*t+x0
Forces acting on a body:
F=x''*m + x'*B +x*k
oscillation of a body:
w=(k/m)^.5
every one of those equations involve a mass. Only the frequency equation involves a force (k is expressed as force/distance). All require that you know the mass.
Newtonian physics is an approximation of relativistic physics, where x'<<C. It is a very good approximation, well within the limits of measurable and significant accuracy for practical purposes.
You can make life as complicated as you want, but why make it unnecessarily so? life and reality are about making approximations. Accuracy of 1 part in 1000000000 is not a necessity, and likely unmeasurable for practical purposes.
A 6 year old kid can solve the equation of motion in a 1 g field, using nothing but approximations and intuitive estimations of all the variables-without having to resort to bent space. That's how you catch a baseball or stop a soccer goal. HE can even make a reasonable guess at the forces resultant --as in "That's going to hurt!" and get out of the way!
ETC: the force equation also involves K. Defining a force with a force...dadgum!

 

[69dodge]

nope--the gravitational field is exerting an acceleration on your mass. The ground (or scale) is resisting that acceleration of your mass with a force exactly equal to your mass times the acceleration. That is what the scale reads.

You're using the word "acceleration" differently from how it's usually used. Acceleration is a kinematic concept: it simply describes the motion of a body, without regard to the causes of that motion. Specifically, it's the rate of change of the body's velocity. If I stand motionless on a scale and remain motionless, my velocity is not changing, and therefore my acceleration is zero.

What does it mean to say that gravity is "exerting an acceleration" on me, if in fact I am not accelerating?

If gravity were a force, the value of weight would be constant, and we would all weigh the same.

Just because it's a force, why does that mean its strength has to be constant? The Earth exerts a stronger gravitational force on a more massive body, and a weaker gravitational force on a less massive body.

Would you say, "if electrostatic force is a force, then all objects have equal charge"?

 

[FortyTwo]

There seems to be a consensus in this thread that a device that was based on the complete elimination of friction might not be called a PMM at all.

Exactly. Such a device simply obeys Newton's First Law. A body in motion continues its motion unless there is a force acting on it.

In the real world, which is where all Challenge demonstrations are held, it is not possible to eliminate all friction. That would be a violation of the second law of thermodynamics.

 

[davefoc]

In the real world, which is where all Challenge demonstrations are held, it is not possible to eliminate all friction. That would be a violation of the second law of thermodynamics.

That seems interesting. How does the second law of thermodynamics preclude the possibility that friction can be eliminated?

Take for instance the gyroscopes in the gravity probe b experiment. It seems like friction could be completely eliminated there if a perfect vacuum could be obtained. Does the second law of thermodynamics preclude the possibility of a perfect vacuum?

I would guess that all materials will occasionaly lose an atom to evaporation even when the material is very cold. Is that the mechanism that precudes a perfect vacuum? Maybe the second law of thermodynamics precudes a perfect vacuum because it precludes the possibility of a pump that could create a perfect vacuum?

 

[FortyTwo]

That seems interesting. How does the second law of thermodynamics preclude the possibility that friction can be eliminated?

Take for instance the gyroscopes in the gravity probe b experiment. It seems like friction could be completely eliminated there if a perfect vacuum could be obtained. Does the second law of thermodynamics preclude the possibility of a perfect vacuum?

I would guess that all materials will occasionaly lose an atom to evaporation even when the material is very cold. Is that the mechanism that precudes a perfect vacuum? Maybe the second law of thermodynamics precudes a perfect vacuum because it precludes the possibility of a pump that could create a perfect vacuum?

If, by gyroscope, you are referring simply to a mass that is spinning in free space unsupported by any other object and having no interaction with any other object, then, assuming you could create, and maintain, a perfect vacuum, you would have a device which follows Newton's first law - a body in motion stays in motion unless acted upon by some force.

However, this is hardly a machine. Not to mention, that there is no pump that can create the required perpetual vacuum.

 

[davefoc]

...
In the real world, which is where all Challenge demonstrations are held, it is not possible to eliminate all friction. That would be a violation of the second law of thermodynamics.

I supect that you are right FortyTwo that it is not possible to eliminate all friction. This just makes sense from the general conscept that making most physical parameters exactly any value is very difficult if not impossible.

The thing I was curious about was how is reducing friction to zero a violation of the second law of thermodynamics.

 

[FortyTwo]

I supect that you are right FortyTwo that it is not possible to eliminate all friction. This just makes sense from the general conscept that making most physical parameters exactly any value is very difficult if not impossible.

The thing I was curious about was how is reducing friction to zero a violation of the second law of thermodynamics.

Friction is a force opposing motion present wherever two materials move against each other. Friction results in the dissipation of energy primarily in the form of heat. Because friction is present to some degree for any two materials which move against each other, the only way to eliminate friction is to eliminate the contact and movement between the materials. The second law of thermodynamics states that energy is irreversibly dissipated from all systems. A system which has no friction (for example, a hypothetical frictionless bearing) would have no irreversible loss of energy and so would be a violation of the second law. Therefore, no frictionless system can be constructed.

 

[AgingYoung]

Davefoc,
I mentioned the 'force of gravity' and caused so much discussion I'm just now catching up with it and all the links that were posted. The points were excellent. I hesitate to answer this question.

It does not sound like AgingYoung proposes to completely eliminate friction from his device. So if the device is to keep moving the device must contain a method for generating enough of an energy surplus at a minimum to replace the energy lost due to friction. And my question still stands: What does AgingYoung think the source of that energy would be in his device

I do plan on minimizing friction yet not eliminate it. You can make cad models and set pin friction and air drag to zero and they'll spin forever. Energy is one of those words similar to gravity. It causes a lot of discussion. If I followed the discussion the conclusion was 'with large masses and large distances gravity is best thought of as an acceleration yet within the limits of the earth it might be considered a force.' I prefer to consider it a force. I don't plan on launching this gravity wheel.

Energy powers an electrical circuit but what happens is a difference of potential. The difference between the source and ground pushes (or pulls, who knows which way it's going?) the electrons thru the circuit. In a similar fashion you add energy to a straw/soda and by decreasing the pressure at the top of the straw the atmosphere (14.7pounds/square in.) pushes on the surface of the soda and gives you a drink. In both cases there's a difference of potential, either electrical or pressure, and work was accomplished.

Now frankly I believe that the energy powering gravity is 'the stretching of the heavens' or as it's been described by those that have looked at the hubble data 'the accelerating expansion of the universe'. I think, as some have suggested in the expanding/contracting model of the universe, that if it reaches its end and starts heading back this way we're in big trouble. Who knows. I don't think anyone knows exactly what 'gravity' is. When I consider the idea that it's an acceleration I think that's a derived quantity. Calculations are as much of a fiction as corporations (legal fictions) but gravity is very real.

What I'm attempting is to drive the axis of orbiting and equal masses with the difference of force that exists between their different moments.

There are two concepts that I'm attempting to model. The last idea that I posted with an accelerated shift of the center of gravity (or mass) didn't incorporate either of those ideas but I thought it might have merit. I just did a test on it and it behaves about how you'd expect a single mass to rotate. There's no difference.

Gene

 

[AgingYoung]

Davefoc,

I just tested a wheel that approaches what I'm trying to model. If I allow it to drop from top dead center (not pushing it) it manages to spin 315 degrees. No cigar but moving in the right direction. I'm using both of the ideas that I think will kick entropy's backside in this one. One thing that I need to do is to cause the weights to shift sooner, another is to cause them to move further. Some how I need use the work that the wheel is producing to do that. When I look at a spreadsheet of momentary torques (1/2 degree intervals) and consider a shift sooner there's an appreciable difference in 2 radians of rotation. It amounts to an average torque of 15.9% of the total weight of the system.

Gene

 

[Ririon]

Davefoc,

I just tested a wheel that approaches what I'm trying to model. If I allow it to drop from top dead center (not pushing it) it manages to spin 315 degrees. No cigar but moving in the right direction. I'm using both of the ideas that I think will kick entropy's backside in this one. One thing that I need to do is to cause the weights to shift sooner, another is to cause them to move further. Some how I need use the work that the wheel is producing to do that. When I look at a spreadsheet of momentary torques (1/2 degree intervals) and consider a shift sooner there's an appreciable difference in 2 radians of rotation. It amounts to an average torque of 15.9% of the total weight of the system.

Gene

315 degrees! Wow. Without knowing the specifics of the construction, that gives an efficiency of roughly 75 %. (An unbalanced wheel with no moving weights rotating 315 degrees from TDC before stopping would have 75 % of it's initial potential energy left.) It seems it is just a question of time before this system passes 100 %! Please keep us posted....

 

[Molinaro]

Anywho. I'm not going to say any more about what makes it work than that the energy comes from natural sources.

You do realize that if your machine uses any kind of external source for that 'natural energy' you refer to.. it's not a perpetual motion machine. It would simply be a machine!

 

[FortyTwo]

315 degrees! Wow. Without knowing the specifics of the construction, that gives an efficiency of roughly 75 %. (An unbalanced wheel with no moving weights rotating 315 degrees from TDC before stopping would have 75 % of it's initial potential energy left.) It seems it is just a question of time before this system passes 100 %! Please keep us posted....

It's those last few degrees that are so darned tricky.

 

[mbuehner]

Look, in order to maintain air speed velocity, a swallow must beat its wings 43 times a second, am i right?

 

[rwguinn]

Look, in order to maintain air speed velocity, a swallow must beat its wings 43 times a second, am i right?

European or Afrcan swallow?

 

[AgingYoung]

315 degrees! Wow. Without knowing the specifics of the construction, that gives an efficiency of roughly 75 %. (An unbalanced wheel with no moving weights rotating 315 degrees from TDC before stopping would have 75 % of it's initial potential energy left.) It seems it is just a question of time before this system passes 100 %! Please keep us posted....

Ririon,
I've managed to get my 'flywheel' to rotate 330 degrees. I need an average of 25.57% of the weight in torque at that point to get it over the hill. 83.3% efficient. At the point it stops I need 1/2 the weight in torque but over the last 30 degrees the average is about 25%. I have an idea for a modification...


FortyTwo, like you said it's those last few degrees that are so darned tricky. I am moving in the right direction. Something that is strange is that I'm doing the opposite of what I imagined I should be doing. It's counterintuitive for me but then so is the idea that gravity is a conservative force.

Gene

 

[Thing]

it's those last few degrees that are so darned tricky. I am moving in the right direction.

Well, water runs downhill. But if you add cornstarch it runs down slower. Maybe if I add enough it'll start to run uphill. It's those last few metres per second that are so tricky. But I'll be moving in the right direction too.

 

[Ririon]

Ririon,
I've managed to get my 'flywheel' to rotate 330 degrees. I need an average of 25.57% of the weight in torque at that point to get it over the hill. 83.3% efficient. At the point it stops I need 1/2 the weight in torque but over the last 30 degrees the average is about 25%. I have an idea for a modification...


FortyTwo, like you said it's those last few degrees that are so darned tricky. I am moving in the right direction. Something that is strange is that I'm doing the opposite of what I imagined I should be doing. It's counterintuitive for me but then so is the idea that gravity is a conservative force.

Gene

330 degrees is not qualitatively different from 315 degrees. Give us 360 with energy to spare.

A weight is not a torque.

 

[AgingYoung]

Ririon,
The mass on a moment arm has a weight that produces torque. To balance the arm in the moment it stops I'd need 50% of the weight at 90 degrees or 100% of the weight at 30 degrees. To cause it to move all the way to 360 or zero degrees I'd need an average of about 26% of the total weight at 90 degrees. That's what I was trying to say.

I'm working on the other 30 degrees now. Maybe I need more cornstarch.

Gene

 

[opqdan]

You can continue to work on it (nobody will stop you from wasting your time), but I fail to see the point in your continual postings. A full rotation is as far as the wheel could rotate in a perfect system (a perfect system would have no friction or other losses on the wheel). Much like a graph of y=1/x approaching an asymptote of y=0, you will never get there and will surely never pass it.

I forsee your future posts taking on this format:
"Okay I'm at 359 degrees"
"now I am at 359.9 degrees"
"Today I am at 359.99 degrees"
"Guess what! I got 359.999 degrees today, just a little further!"
"I can almost smell the money rolling in. Today I hit 359.9999 degrees!"
... ad nauseam ...