# What is the most efficient machine? **URL:** \ **Category:** Factual Questions\ **Created:** [May 9, 2001, 10:10pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913 "2001-05-09T22:10:47Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 11, 2001, 7:52am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/41 "2001-05-11T07:52:22Z")
> [@](#): > > \>\> most of the time, when we say “efficiency,” we really mean "economic efficiency > > Well, you can say and mean whatever you like but that is not what the OP says and I doubt it is what it means I should have thought the OP through a bit more, but to reiterate: > [@](#): > > I think what I was actually meaning to ask is What is the most efficient engine in terms of the amount of mechanical work (or kinetic energy) out in relation to the amount of chemical energy available from the fuel. Animal/human bodies are still valid in this as ‘biological engines’. By fuel, I think I meant chemical energy available in the form of fossil fuels, carbohydrates, biomass, hydrogen etc. I don’t think that I’d really be happy with accepting electical energy as a fuel unless you’re going to factor the efficiency of whatever process generates it, so, for example, a machine that has it’s own solar panels would be OK (although I’d take ‘fuel’ to mean ‘the available energy in sunlight’). Anyway, if nothing else, this has been a lesson in how to ask the question properly, so thanks people. ---
**Author:** ![Andy](https://avatars.discourse-cdn.com/v4/letter/a/aeb1de/32.png) [@Andy](https://boards.straightdope.com/u/Andy)\ **Post date:** [May 11, 2001, 9:34am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/42 "2001-05-11T09:34:57Z")
> [@](#): > > \*Originally posted by Britt \* > Electric heaters can look to be very efficient isolated systems, providing you are looking at an enclosed, water (or even better oil) heaters. Fan based systems on the other hand have nowhere near this efficacy. Even coil-based systems are not as good. > Unfortunately as a useful machine a heater by itself is practically useless. It’s not the input I would question as much as the desired output. In most cases the output of a heater is not just heat but heat contained within a given area, which is to a large extent dependent on the environment, which would have to be considered part of the ‘machine’ generating the output. > A heat sink on the other hand makes an interesting case study. Efficiency and efficacy are different concepts. I don’t think you can measure efficacy as such. As for an electric heater failing to fulfil its desired role, what the hell does this have to do with efficiency? Electric heaters are not completely efficient, I’ve _heard_ them. ---
**Author:** ![Abe](https://avatars.discourse-cdn.com/v4/letter/a/f1d935/32.png) [@Abe](https://boards.straightdope.com/u/Abe)\ **Post date:** [May 11, 2001, 10:09am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/43 "2001-05-11T10:09:41Z")
> [@](#): > > _Posted by Anthracite_ > Electric heaters are not completely efficient, I’ve _heard_ them. You also see them glow red-hot. I don’t think there’s any such thing as a 100% efficient machine of any kind. How does photosynthesis rank in terms of overall efficiency? Plants are essentially energy-collecting machines, since they don’t expend too much energy during their lives. I realize that plants don’t have very much in the way of immediate output but we can release large amounts of energy by burning them (fresh or fossilized), so I may be stretching the question a bit to include fuel … ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [May 11, 2001, 11:28am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/44 "2001-05-11T11:28:36Z")
> [@](#): > > \*Originally posted by Abe \* > \*\* > > > [@](#): > > > > _Posted by Anthracite_ > > Electric heaters are not completely efficient, I’ve _heard_ them. > > You also see them glow red-hot. I don’t think there’s any such thing as a 100% efficient machine of any kind.\*\* I didn’t post that. 😕 ---
**Author:** ![Abe](https://avatars.discourse-cdn.com/v4/letter/a/f1d935/32.png) [@Abe](https://boards.straightdope.com/u/Abe)\ **Post date:** [May 11, 2001, 11:48am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/45 "2001-05-11T11:48:18Z")
My humblest apologies, Anthracite! I must have selected the wrong item when I posted the quote. The correct poster was android209. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [May 11, 2001, 3:53pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/46 "2001-05-11T15:53:44Z")
for practical purposes electric heaters are 100% eficient. Now if you want to quibble and nitpick… IR light ends up as heat too. I guess you could say a lightbulb emits more light and some could escape through an uncovered window… yes, insignificant but yes. Close the window. A lightbulb would not be considered a heater but, even in this case if you add light plus heat you get 100% and the light is converted into heat also. Noise: again the amount of noise from a heater is a tiny fraction of the output and it also ends up as heat. You could add electromagnetic losses. Again they are an insignificant fraction. This reminds me of a dumb argument I had years ago with a woman who said _every_ form of heating a room consumes oxigen, just some more than others. She was adamant about this. She couldn’t explain it but she was adamant. So someone comes in the room and she asks “isn’t it true that hat water radiator consume oxigen?” and he, trying to be diplomatic" said “well… I guess so, as they rust” and she felt vindicated and “proved” the rest of us were ignorant fools. ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [May 11, 2001, 6:58pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/47 "2001-05-11T18:58:35Z")
> [@](#): > > \*Originally posted by Crafter\_Man \* > Nope, sorry. When you calculate efficiency, you must look at the **whole** system, not just a small part of it. To make an electric heater produce heat, a power plant must produce electrical power by burning coal or gas (or whatever), making steam, turning a generator, etc. The power must then be delivered to your house via (resistive) conductors, transformers, etc. Anyway, when you look at the **whole** system, the “100% efficient” electric heater doesn’t look so hot after all. (Pun intended.) You forgot to account for the work used to mine the fuel, refine it and deliver it. I think what the OP had in mind, simply, is how efficiently does the most-efficent INDIVIDUAL machine turn energy into work? What is the ratio of energy used to energy lost? An electric heater would be such a machine; all the other stuff you mentioned is just the fuel delivery system. As far as humans on bicycles, see this entry from ["How Stuff Works](http://www.howstuffworks.com/question527.htm): > [@](#): > > a person riding a bicycle at 15 miles per hour (24 km per hour) burns 0.049 calories per pound per minute. So a 175-pound (77 kg) person burns 515 calories in an hour, or about 34 calories per mile (about 21 calories per km). > > A gallon of gasoline (about 4 liters) contains about 31,000 calories. If a person could drink gasoline then a person could ride about **912 miles on a gallon of gas** (about 360 km per liter). That’s better than any motorcycle. In 1972, I had a Yamaha 60cc Mini-Enduro [sub]TM[/sub] that got 100 MPG. I don’t think any current motorcycle can do better. ---
**Author:** ![\_Uigi](https://avatars.discourse-cdn.com/v4/letter/_/e9a140/32.png) [@\_Uigi](https://boards.straightdope.com/u/_Uigi)\ **Post date:** [May 11, 2001, 9:08pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/48 "2001-05-11T21:08:59Z")
The LEVER. 1. essentially no loss of efficiency due to friction, 2. capable of outputting any multiple of input power, 3. no moving parts, 4. may be built to any size that’s needed, 5. (I’m certain it has other attributes, but I’m too lazy to go look right now) (Sailor, I think you had the right idea earlier) ---
**Author:** ![Britt](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Britt](https://boards.straightdope.com/u/Britt)\ **Post date:** [May 11, 2001, 9:12pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/49 "2001-05-11T21:12:03Z")
\*\*Andy \*\* This then reduces down to all machines been equally efficient, as mentioned elsewhere in order to have any meaning the question is really about ‘desired output’ for a given input. In this case the desired output is not actually heat but heat contained with an area. **sailor** Well you have already dismissed the electromagnetic radiation at frequencies above infrared that tend to be generated from a coil based heating system. I still feel that the purpose of the heater was to raise the mean energy of the surrounding medium, which non-infrared light is not terrible effective at doing. Fan heaters on the other hand are producing a large amount of additional kinetic energy to the medium at the macro level and thus this energy is not going into heating but rather into distribution. Finally as the question has now been redefined as pertaining to ‘raw inputs’ electric based systems become much harder to justify. Where as my heat sink is starting to look very good. As soon as I can determine a reasonable manner for determining the efficiency of them with regards to the present enquiry I’ll put up some figures. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [May 11, 2001, 10:15pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/50 "2001-05-11T22:15:52Z")
jab1, as has been explained, muscles are very inefficient machines. A guy on a bicycle can go as far as you say but comparing it to a motorcycle is meaningless because the motorcycle is going much faster and overcoming much more friction. I can assure you that if you take a rail car and fit it with a diesel motor, it will be _way_ more efficient than if the people on the car were pedaling to move it. ---
**Author:** ![Saltire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saltire/32/553_2.png) [@Saltire](https://boards.straightdope.com/u/Saltire)\ **Post date:** [May 11, 2001, 11:09pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/51 "2001-05-11T23:09:28Z")
I’m sure this won’t be a welcome post, since it trails away from the redefined question, and contains absolutely no information to back up what I’m going to say. But, I’ll say it anyway, in case anyone wants to hear it. I once read that the electrical transformer is very efficient, in terms of power input/output. They do generate a good bit of heat and I assume some of the energy is lost in the parts of the primary fields that don’t intersect the secondary coil, but that’s what I heard. Is there anything to this assertion? I don’t know. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [May 11, 2001, 11:58pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/52 "2001-05-11T23:58:06Z")
Yes, my Power Plant Handbook here says that large, really high-voltage power plant transformers work with more than 99.5% efficiency, and some can work at 99.96% efficiency in rare cases. It also says that they become more efficient as they get larger too. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [May 12, 2001, 12:37am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/53 "2001-05-12T00:37:16Z")
Anthracite, it is my experience that most machines get more efficient as they get larger. Generally this is to be expected. Transformers can be made very efficient but generally you want to strike a balance between cost and efficiency. Internal combustion engines also get more efficient as they get larger and this is to be expected as friction diminishes as a part of the whole process. a small 50 cc motor has much more friction (in proportion) than a large truch diesel. I would question whether an electrical transformer fall within the definition of “machine” … I guess f a lever or gear box is a machine, then an electrical transformer is also a machine. Note that,as we have mentioned, a lever or a set of gears _also_ have _very_ high efficiency, probably higher than a transformer. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [May 12, 2001, 12:59am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/54 "2001-05-12T00:59:09Z")
Wait…how did we come to the conclusion that a gearbox is an extremely efficient machine? Automobile gearboxes lose a decent amount of horsepower in them, and so do industrial gearboxes. Overall they are very efficient, but 99% or up…? I would really have to question that. ---
**Author:** ![ModernRonin2](https://avatars.discourse-cdn.com/v4/letter/m/c37758/32.png) [@ModernRonin2](https://boards.straightdope.com/u/ModernRonin2)\ **Post date:** [May 12, 2001, 5:45am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/55 "2001-05-12T05:45:28Z")
Three points… - In terms of “distance per energy expended”, I’ll have to go with the person on a bicycle too. - As a nomination for the most efficient engine, I nominate The Stirling Engine: [http://www.howstuffworks.com/stirling-engine.htm](http://www.howstuffworks.com/stirling-engine.htm) (However, it would not surprise me to find out that a well-designed electric motor is much more efficient than this.) - For something to be a “machine” in my mind, it must have physically moving parts. A transformer alone doesn’t count. Though by this definition, a screw or door wedge might not be a machine. Oh well. -Ben ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [May 12, 2001, 6:39am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/56 "2001-05-12T06:39:45Z")
Anthracite, the mechanical equivalent of a transformer would be a single gear, not a complete gearbox. I believe a single gear coupling can be pretty efficient transferring power. I doubt the losses for a well designed gear would be greater than 1 or 2% (I am making that up, I have no support). A gearbox is not so efficient due to several factors but it is not the mechanical equivalent of a simple transformer. Anyway, my guess is that the efficiency of a simple lever is way up there with an electrical transformer and a simple gear can’t be far behind. Note also that smaller transformers are not so efficient ---
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://boards.straightdope.com/u/matt)\ **Post date:** [May 12, 2001, 10:23am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/57 "2001-05-12T10:23:12Z")
Bit of a mixed bunch of examples here! Some definitions, which are more or less my own and not set in stone: A **machine** is a device for transmitting and/or multiplying **force**. A lever is a machine, an inclined plane is a machine, a hydraulic ram is a machine, a crowbar is a machine. Hell, a stick is a machine if you use it to prod something. When the parts of a machine move, you are transmitting energy through it. You lose some energy through friction and other mechanisms, but overall the energy transmission efficiency can be high. Anyone want to guess the efficiency of a screwdriver, assuming we allow it to be a machine? A **transducer** is a device for converting one form of energy into another. A lightbulb is a transducer, a loudspeaker is a transducer, a heating element is a transducer, an electric motor is a transducer. Transducers almost always convert some of the energy into heat. If heat is the desired energy output, transducers can be 100% efficient. A **heat engine** is a device for doing work by allowing heat to flow from a high temperature heat source (usually a combusting fuel) to a lower temperature heat sink (usually the planet.) All IC engines are heat engines, steam turbines are heat engines, stirling engines are heat engines. The maximum theoretical efficiency of a heat engine is determined by the temperatures of the heat source and sink. The 4-stroke gas engine is actually a more efficient heat engine than the diesel, but the diesel does better because its heat source is effectively at a higher temperature (higher compression ratio). It’s not fair to compare heat engines with other transducers or machines - they all do very different things. It’s not fair to compare the “efficiency” of an electric motor or a clockwork motor with a heat engine - they’re going to beat it hands down. The form of energy being supplied to an electric motor or a clockwork motor can be regarded as “stored work” - equivalent to a raised weight. The form of energy supplied to a heat engine is entirely different. So my “most efficient” votes are: machine - the push rod! transducer - resistance heating element heat engine - the stirling engine, w.r.t. theoretical max. (Carnot cycle) heat engine - combined cycle power plant, w.r.t. overall efficiency. chemical energy conversion - the electrochemical cell force amplifier - lever vehicle transmission - a nice, well lubed bicycle chain? stored energy - the raised weight in an old clock light source - luciferin oxidation used by fireflies heat your house - burn a fuel in a stirling engine-powered heat pump transport - calorie/ton/mile- horse drawn barge? long distance energy transmission - gas pipeline One for **Anthracite** : - many years ago I saw a scheme for a combined cycle power plant where the highest temperature stage produced _plasma_: the fuel and air were preheated via heat exhangers to give a monstrous temperature of combustion. Some energy would be extracted from this via magnetohydrodynamics before the plasma was used to boil water. D’you know anything about this, and what became of it? ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [May 12, 2001, 11:51am UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/58 "2001-05-12T11:51:42Z")
> [@](#): > > \*Originally posted by matt \* > \*\*One for **Anthracite** : - many years ago I saw a scheme for a combined cycle power plant where the highest temperature stage produced _plasma_: the fuel and air were preheated via heat exhangers to give a monstrous temperature of combustion. Some energy would be extracted from this via magnetohydrodynamics before the plasma was used to boil water. D’you know anything about this, and what became of it? \*\* :eek: No, I never heard of that, and my usual searches have not turned up anything yet. Very interesting! ---
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://boards.straightdope.com/u/matt)\ **Post date:** [May 12, 2001, 12:36pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/59 "2001-05-12T12:36:10Z")
Britannia has some articles on the things: [http://208.154.71.60/bcom/eb/article/7/0,5716,108547+3,00.html](http://208.154.71.60/bcom/eb/article/7/0,5716,108547+3,00.html) ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [May 12, 2001, 5:59pm UTC](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913/60 "2001-05-12T17:59:06Z")
That magnetohydrodynamic generator isn’t exactly new; the first experiments were conducted by Michael Faraday in 1832. > [@](#): > > Depending on the heat source and magnetic field strangth, power densities of 10 to 500 megawatts per cubic centimetre in the duct can be obtained. The first practical device was not built and operated until 1963, however, by the Avco research laboratory. They got 33 megawatts out of it. [Previous page](https://boards.straightdope.com/t/what-is-the-most-efficient-machine/64913.md?page=2)