Perpetual motion machine ?

[hedgewizard]

*applauds* It's pretty old fashioned, not unlike the poster.

[colhut]

Perpetual motion is easy ! Just pop an old bicycle wheel in orbit and spin it, job done. With the exception of re-entry or a collision with space debris it will continue to spin, there being no other forces to act on it.

The problem occurs because always somewhere sombody thinks there is energy to be taken out of the system without affecting it, logically this just cannot be done. Theres no such thing as a free lunch! Whatever energy is removed from the system had to come from somewhere.

[john]

Perpetual motion is easy ! Just pop an old bicycle wheel in orbit and spin it, job done. With the exception of re-entry or a collision with space debris it will continue to spin, there being no other forces to act on it.

The problem occurs because always somewhere sombody thinks there is energy to be taken out of the system without affecting it, logically this just cannot be done. Theres no such thing as a free lunch! Whatever energy is removed from the system had to come from somewhere.

Hi Colnut,I'm confused. YOU have just told me and everyone else how perpetual motion can be achieved,simply done by spinning something up in space.
Then in the next breath you are telling us,the problem accurs when we try to get energy from it. WHY do you say that,has any body tried spinning a wind turbine system up in space. I would say NO,because no one has thought to find out if they can generate energy this way. If something moves it can great an effect once put in motion.
Another outside of the box idea of mine which someone might like to try or has already been tried. I might just get a free lunch if it hasn't been tried out before,and maybe a drink too,either way I thought I would share my thoughts with you. May we all live long and happy. John. J.R.P.

[Martin]

ahhhhhhh! - if you have something like a saucer, spinning silently in space, if it's in a vacuum, in zero gravity, it'll just go on and on forever (ish), BUT the vacuum and lack of gravity doesn't get over the "drag" that a turbine would impart.
If you plonk a wind turbine on your lap, short the cables out, and try turning it, the "pull" of the magnets can be felt - there is a definite "resistance" that would still be there in space - so if you got your turbine into space, and spun it by hand, it would still slow down and stop, because of the "drag" of the magnets, and the friction of the bearings!
I'm all for tall masts to get them up out of turbulent air, but I reckon that may be a touch too high! - there is also the problem of cable losses, and quite what to attach it to on the way down from space - might be a bit pricey too - a few hundred yards of turbine cable costs a fortune!

[The Chili Monster]

John wrote:

Mr. Green Confused Hi Colnut,I'm confused. YOU have just told me and everyone else how perpetual motion can be achieved,simply done by spinning something up in space.

Colhut wrote:

With the exception of re-entry or a collision with space debris it will continue to spin, there being no other forces to act on it.

John - it's Newton's First Law of Motion: a body remains at rest or in motion with a constant velocity unless acted upon by an external force
BTW, John, you may be right in that they haven't tried out a wind turbine in space (but then why would they? Wind is basically a reaction of air particles to heat given off the Earth's Surface (Convection); no air in Space!). However, scientists and engineers have created vacuum conditions on Earth: think cathode ray tubes (JJ Thomson, late 19th century) and that F-OFF particle accelerator as maintained by CERN under Lake Geneva.

[Martin]

ps, the only thing I've ever come across that gets anywhere near
"perpetual motion" are my daughter's vocal chords, particularly when armed with a telephone or two!

[Muddypause]

...And Now In Colour:

Hi Colnut,I'm confused. YOU have just told me and everyone else how perpetual motion can be achieved,simply done by spinning something up in space.
Then in the next breath you are telling us,the problem accurs when we try to get energy from it.

What it's important to try and grasp, John, is that motion and energy are two different things. And if you want work to be done, you have to have both of them. One on its own is not enough.

You can have something in motion (for example a spinning bycycle wheel on very low friction bearings), but on its own, you won't be able to do any work with it. If you tried to get that wheel to drive a generator, it would simply stop.

You can also have a store of energy (for example, the energy contained in a great big wound up spring), but again, on its own, that spring cannot do any work for you.

But if you connect the spring to the wheel, then for a little while the wheel would be able to do work by running a small generator. But as soon as the wheel stops, or the spring is unwound, then you can't get any more work done.

If you confuse energy with motion, then you might find yourself always designing brilliant machines, and yet never quite sure why they don't work. They are two different things, and your machines must have both of them.

[Wombat]

I like the idea of a wind generator in space - in space no-one can hear you scream - when it doesn't work!

Nev

[john]

Hi ALL,they say it's good to talk,that's why it does me good to share my thoughts with you,because I suffer with short term memory lose,so I have trouble remembering what I might have read anyway.
So far what I've read is there is a difference between energy and motion,then try to picture this using a light sourse. Say you had a very long tube coated on the inside with a mirror like surface,with say some very small holes made in it to see the light in side,but not enough to cut down the light on the mirrors. NOW comes the main point. If you were to add a very short sharp burst of bright light for a millisecond,would that same bright light continue going around and around inside the tube because there are no pressures on it motion wise. John. J.R.P.

[Martin]

I think the problem with that is that generally, light won't bend - to get round your mirrored tube it has to "bounce" round the walls - each time it "bounces" it loses power (I don't know of any "perfect" mirrors).......

[john]

I think the problem with that is that generally, light won't bend - to get round your mirrored tube it has to "bounce" round the walls - each time it "bounces" it loses power (I don't know of any "perfect" mirrors).......

Hi Martin,I should have said mirror like surface,like chrome or aliminume foil,plus I would have thought it would depend on how much you bent the tube. The reason I said about a light sourse is,it starts from a spark or element sending out the light sourse first,which we can see when the light sourse is at its brightist,which I thought one millisecond of power would have created. As for light bouncing it must lose power. I suppose that would depend on how far the reflective surface was apart and how many times you needed to start the whole process over again with very little power to be used at the start. John. J.R.P.

[Muddypause]

It's a good question, John. And it gets more puzzling when you think what would happen if you turned the light source out. Would the inside of the mirrored tube go on being lit up by all the light that just goes on bouncing around in there? In fact, if you keep the light source on, why doesn't it go on getting brighter and brighter, because none of the light is getting out. And if you later broke open the tube, would all that light come spilling out, even when the light source had already been turned off?

In fact we can simplify that tube a bit. If the light source only emits light of the visible spectrum (ie, no infra-red, or ultra violet, or other wavelengths - just the stuff that we can see), then you only need to paint the inside of the tube pure white; no mirrors needed. Pure white, by definition, will reflect all the light.

I don't know the answers to these questions, but I have been thinking about it all afternoon. Suppose your tube was the size of the universe. We know that it takes the sun's light over 8 minutes to reach earth. This means that if the sun suddenly went out, we would still be getting its light for a while before it went dark. If we lived a light-year away from the sun, we would still get its light for a year after it went out. This must mean that the light is travelling through space regardless of whether the light source is still there or not. And when it hits the surface of another planet, some of it will be reflected, and will continue off in another direction. And if, instead of planets, there was just the inside of your universe-sized tube there, with its pure white surface, surely the light must just go on bouncing around, even when the light source is gone.

But I suppose not all of it will be reflected - it's hard to think that in nature there can possibly be a perfect reflector. Some of it will be absorbed by the surface it hits, and will be converted into heat. We know this happens when we sit in the sun and get hot. So in reality, the tube will just warm up until all the light has been absorbed. In terms of a small tube, this would probably be almost instantaneous. And in any case, you would never be able to get more energy out of the tube than you put into it in the first place, whatever happened to the light.

Light is a peculiar thing that I don't even begin to understand fully. Some people say it behaves like a wave, some say it behaves like particles, and some say it does both at the same time. If you shine a light into a dark room, the room lights up. But if you shine a bright light into an empty space - say up into the sky on a clear night - the sky doesn't light up. This is because we can only see things that the light bounces off. It's weird to think that in a brightly lit room, the actual space in that room is not lit up at all, only the things in it. The space between our eye and the object is... well it's not anything - it's not bright, nor is it dark. It's just an empty nothingness, even though whatever is around it is brightly lit.

And it's stranger to think that if everything in the room is painted pure matt black, the walls as well, then when you turn the light on, it will still be absolutely dark in the room, and you still won't be able to see anything, because pure black doesn't reflect any light. If something is pure black, you can never see it, only its shadow.

[colhut]

Ahhh, I love the light analogy, and I can shine some light on it (sorry )

:Say you had a very long tube coated on the inside with a mirror like surface,with say some very small holes made in it to see the light in side,but not enough to cut down the light on the mirrors. NOW comes the main point. If you were to add a very short sharp burst of bright light for a millisecond,would that same bright light continue going around and around inside the tube because there are no pressures on it motion wise. John.

instead of shining extra light lets reduce the problem. we will have a long tube completly coated with a perfect mirror substance. and we will have a single hole for observation. Into this chamber we introduce a single photon of light. This photon would bounce around inside our tube structure indefinitly until it exits the chamber through our viewing hole and into the eye of the observer (as the human eye cannot see a single photon we'd better have a photon detector there to see it). The point is though that our photon of light is no longer in the chamber it has left ( the chamber is now dark), the energy has left the perpetual motion system and has been seen by the detector. this holds true for one photon or indeed if you flood the chamber with light. you only get to see it once it leaves the system. The problem with your anology John is that you cant have a hole in your chamber and not expect the light to leak out of it. by definition the hole is a non reflective part of the surface area and the probability is sooner or later that the photon of light will hit it and not be reflected. I agree with muddy, it is fascinating the way that light can be seen to behave both as a wave (with characteristics of constructive and destructive interference) but also as a particle (affected by gravity therefore infering mass). If you are at all interested then I recommend reading "The strage theory of light and matter" by Richard Feynman, This is not a heavyweight read but a small paperback and covers the subject without recourse to horendous formulas.

Light can be made to bend. but it does take a lot to do it, a photon of light when considering it as a particle has mass and is therefore affected by gravity. During a lunar eclipse there is a grey fug around the moon, this is where the light that just misses the moon but passes close enough to be affected by its gravity and over a long distance. The effect is just enough to bend some stream of photons back to earth.


getting back to perpetual motion and work done. if you want your generator to output 1Kw, then it will need to be supplied with more than 1Kw of energy to do it, some will end up as the electricity you want, some will end up as noise, lots will end up as heat. But that energy has to come from somewhere, a spinning bicycle wheel in space only spins while there is nothing to stop it, strapping a generator to it will provide that resistive force and stop it very quickly. If you wanted you could even work out how much energy was available in the bicycle wheel, I think its Mass X velocity = energy (but I could be wrong there) but its obvious that if I remove some energy from the system then I also either have to change the mass or velocity, as the mass is fixed it must be the velocity that changes until the velocity reaches zero and there is no energy in the system to be harvested.

[Martin]

John's vision sounds quite like the circular particle accelerators used ages ago for "atom smashing" - if I remember right you had a "doughnut", inside which particles were accelerated round and round, held in place by magnetic fields - when the desired velocity was reached, they used a change in the magnetic field to allow the particle to fly out at ginormous velocity!

[colhut]

Yes it certianly does, one of the other things they do is whizz particles around in oposite directions until both are travelling as close to the speed of light as can be attained, then they alter the magnetic containment field and smash them into each other to produce anitmatter (in 10 years they have prodiced nearly a billionth of a gram of antimatter !). What is really nice about the CERN website is you can email them any sensible question and they will attempt to get an answer for you.