It’s easy to design a machine or device where output power exceeds input power.
It’s impossible to create a machine or device where output energy exceeds input energy.
My point is that the title should be changed to, “A machine that generates more energy than it uses.”
Link?
[sup]That’s right, I’m that lazy.[/sup]
When it comes to Mechanical Energy, I get the something for nothing argument. But with Nuclear Breeder Reactors, I get kind of lost. It appears that a Breeder Reactor produces more fissile material than that with which it started. While clearly something is getting used up in the reaction (there’s also energy generation going on in addition to the result of more fissile material than that with which you started) it’s just not clear to me what is being used up in the process.
Can anyone enlighten me on this path?
The fissile material in natural uranium is a small fraction of the total uranium. In a breeder reactor, some of the neutrons released by the fission of U-235 are absorbed by the much more numerous U-238. This creates Pu-239, which is fissile. If you focus of thinking of it as neutrons moving around instead of the amount of fissile material, it makes sense: all the neutrons that are needed to create the “new” Pu-239 are already there in the original uranium fuel.
Oh, yeah, Linky.
I can think of an inexact chemical energy analogue.
When you stack wood in a tight poorly-ventilated pile and light it on fire, you get… heat output, rather a lot, and at the end of the day, another fuel: charcoal.
It’s possible that the total energy available by charring the wood and then burning the charcoal would exceed the total energy released by simple free-air burning of the wood, but in all cases, you’re releasing energy latent in the chemical bonds of the wood’s carbon compounds. What isn’t released in the first round (charring) becomes available by the “ash” of the first round being purer carbon. But you can’t burn charcoal and yield another stage of fuel, so it’s finite.
Similarly, you “burn” U-235 and yield a lot of “burnable” PU-239. The total output energy is comparable to a hypothetical one-cycle burn, and in all cases you’re releasing energy latent in the nuclear bonds of those atoms. When you burn the plutonium, it’s gone. You still can’t get something from nothing.
ETA: I just had a wicked thought. We should start calling charcoal ricks “Carbon breeder reactors” to spin up both the global warming and anti-nuclear factions.
What about heat pumps?
You are Evil and I find your ideas intriguing. May I subscribe to your newsletter?
The output energy doesn’t exceed the total input energy. I.e. the “excess” is an energy input, just from environmental thermal energy, not from our designated input energy source.
What if we build a large planet, so large that the compressive strength of gravity heats up the core. Then we run a heat conducting rod to the center and use the exposed heated end for a steam powered generator. 
<tongue firmly planted in cheek>Right, right. We could call it “Dirt” or something. Well, I’m just guessing, but it seems to me that the surface would probably scuff off some, and there would probably be some layer of loose material there, so people might well figure it was dirt all the way down. Of course, if it somehow wound up with some extensive areas of surface water, we might better call it “Aqua”. Hmmm…
Still, if the inner material was brittle, it would probably crack in various places and we might not need to build that conducting rod after all.</tfpic>
Forget reactors, what about an atomic bomb? Doesn’t that generate far more energy than what went in? Not that the energy is easily harnessed, I’ll grant you . . .
The energy was there all the time, in the bindings between the particles in the nucleus.
Well if you go that route, then every conceivable machine must produce exactly as much energy as was put into it, no more and no less – with the caveat that varying proportions of that energy will be bound up in the form of matter going either in or out. Am I right?
Absolutely correct. It’s called the Principle of Conservation of Energy. Not all of the energy that comes out will be usable (for example, heat loss due to friction), but the basic principle is that energy can neither be created nor destroyed – only changed into a different form of energy (or matter).
To be honest - I think the important part here is the ‘not all energy…’ part. In any closed system, the total amount of energy available to do work is always less than the total energy put into the system - this is entropy which is, in fact, why perpetual motion machines can’t work. If you could even get 100% of the energy back, you could keep the system going forever - entropy prohibits it…
There’s only one known exception - superconductors - and it’s an iffy exception. If you have a superconducting ring and you induce a current, it will continue indefinitely (as long as the ring remains a superconductor). Because of quantum mechanics, if you pick the right energy level, the ring can’t dissipate any energy without violating quantisation rules. So it runs forever.
Thing is, you also can’t use it for anything useful because as soon as you put any load on it - it stops.
That’s true, but using that for anything (such as your rods) will cool the centre of the planet and eventually the planet will collapse to a stable - cold - state.
Also, the amount of energy that you’d put into building the actual planet would be many times bigger than you’d get out. It’s not easy building planets.
Everyone is looking for a perpetual motion machine. Why be so impressed with that. Nature has created an environment full of stored energy that was created years ago. We need to understand that efficient use and moderate conservation of this energy and our natural resources is ok and to respect the planet and the other species that feed us. I can make things that utilize the electromagnetics of the earth to gain power, but this energy field is very dangerous to tap if it is done commercially without insight. We need to quit wasting our resources. Keeping a viable home for mankinds future generations means we can’t have everything we want. If I sound irrational to you than you should look into you’re life and study what you percieve as really necessary. We need food and shelter and companionship and respect of our kind. This new world’s perception has got distorted and people want an easy life. I am no exception.
how about a Tesla coil?
120V in , 10,000V out…
(or is that based on power output as opposed to energy output?)
And the amount of amps in and out?
It you think of electricity as water flowing through a pipe:
[ul]
[li] Volts is the pressure[/li][li] Amps is the amount[/li][li] Watts is the power. For example, if the water was turning a water wheel.[/li]
[/ul]
Increasing the volts decreases the amps, but the wattage remains the same.
Watts = Volts * Amps.
Somewhere, resistance (measured in ohms) comes into it too. But, I wasn’t in class that day.
In simplistic DC terms, resistance figures in by reducing available current and “dropping” some of the available voltage. A series resistance “drops” a portion of the voltage proportionate to its resistance compared to the overall resistance of the circuit. That voltage drop is transformed into something else. Some of a motor’s “resistance” is transformed into mechanical motion (through the magic of electromagnetism, for instance.) A transformer or other coil device generates heat (“wasted”), and may also generate mechanical energy (vibration, buzzing, etc.) A straighforward resistor just generates heat, unless you push it beyond its current or voltage limits, in which case it generates light, loud noise, or magic smoke. :eek: (That’s the voice of experience there.)
AC resistance is more complicated (and is the accurate way to model a transformer), but still works out the same in the end: voltage drop becomes some other kind of energy, whether “useful” or “wasted”.
The other side of a transformer or tesla coil is actually a different circuit, so the input voltage and output voltage are independent (different electrons). The coil arrangement induces higher voltage in the secondary coil at the expense of lower current capability, with the additional bonus that some of the energy input at the primary (input) coil side will be lost as mentioned above.