# Perpetual Motion - is it so damn hard? **URL:** \ **Category:** Factual Questions\ **Created:** [April 14, 2010, 5:44am UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037 "2010-04-14T05:44:34Z")\ **Posts on this page:** 20\ **Page:** 6
**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:** [April 17, 2010, 1:40pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/101 "2010-04-17T13:40:01Z")
> [@johnpost](#): > > > [@yoyodyne](#): > > > > I think someday we will find the so-called “laws” of thermodynamics were only suggestions. Radio, telephones, television, fast trains, airplanes, nuclear power, space flight, and the moon landing were all once declared impossible. > > i think claims of those not being possible was based on technology limitations on the part of the claimant due to engineering as far as they knew it. where claims made not based on engineering? > > laws of thermodynamics is science which is a different view. both natural and man made phenomena have been examined to lead to those beliefs. I agree - it makes more sense to say that because people were wrong when they said powered flight was inpossible, maybe we’re wrong when we say it is possible. Maybe planes just don’t work, and we’re all wrong in thinking they do. Which is silly, but it makes as much sense **yoyodyne** ’s argument about thermodynamics. The assertion that flight was impossible was based on ignorance - the realisation that it _was_ possible was based on research, experiment and observation. The laws of thermodynamics are based on research, experiment and observation - they therefore have much more in common with the realisation that Radio, telephones, television, fast trains, airplanes, nuclear power, space flight, and the moon landing _ **ARE** _ possible than with the ignorant assertions people used to make that they were not. ---
**Author:** ![Stealth\_Potato](https://avatars.discourse-cdn.com/v4/letter/s/d78d45/32.png) [@Stealth\_Potato](https://boards.straightdope.com/u/Stealth_Potato)\ **Post date:** [April 17, 2010, 7:41pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/102 "2010-04-17T19:41:04Z")
> [@katunari](#): > > There are several Laws of Physics stating lots of facts on whatsoever. If the laws cannot explain how this ultimate perpetual motion machine - the macrocosm - works, how precise can they be. Who says the “macrocosm” is necessarily a perpetual motion machine? Look up [the heat death of the universe](http://en.wikipedia.org/wiki/Heat_death_of_the_universe) sometime. ---
**Author:** ![Sapo](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@Sapo](https://boards.straightdope.com/u/Sapo)\ **Post date:** [April 17, 2010, 10:16pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/103 "2010-04-17T22:16:18Z")
> [@Stealth\_Potato](#): > > Who says the “macrocosm” is necessarily a perpetual motion machine? Look up [the heat death of the universe](http://en.wikipedia.org/wiki/Heat_death_of_the_universe) sometime. Thanks, I read that on my mobile and was waiting to get home to respond to it. Also for whoever mentioned the atmosphere as a Perpetual Motion Machine. The Sun is constantly cranking that machine. It is not perpetual motion. I mean, it will move “forever” but not at a gain in energy. ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [April 17, 2010, 10:42pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/104 "2010-04-17T22:42:38Z")
You keep using that word. (forever) I don’t think it means what you think it means. Tris ---
**Author:** ![Sapo](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@Sapo](https://boards.straightdope.com/u/Sapo)\ **Post date:** [April 18, 2010, 4:27am UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/105 "2010-04-18T04:27:23Z")
> [@Triskadecamus](#): > > You keep using that word. (forever) I don’t think it means what you think it means. > > Tris Hence the quotes. ---
**Author:** ![komolono](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/komolono/32/532_2.png) [@komolono](https://boards.straightdope.com/u/komolono)\ **Post date:** [April 19, 2010, 9:48am UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/106 "2010-04-19T09:48:58Z")
> [@Mangetout](#): > > When you extract all the kinetic energy from an object, it stops moving. This sentence opened up my eyes - so it stops. Now I rather start working on a levitation machine. You know World’s magnetic field, vessel as a coil, gravity and vola - it stops. Now you say that you have already tried it… ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [April 19, 2010, 10:13am UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/107 "2010-04-19T10:13:30Z")
It’s **soooo** damn hard. ---
**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:** [April 19, 2010, 10:22am UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/108 "2010-04-19T10:22:46Z")
That’s why a bicycle with dynamo-powered lights is noticeably harder to pedal when you switch the lights on. Spinning the dynamo is easy - but when you start to extract energy from the dynamo, the dynamo resists motion, because that’s where the energy is being extracted from. A moving magnet will induce a current in a conductor (that’s how dynamos work), but that current generates a magnetic field that works to resist the motion of the magnet (this is called Lenz’s Law). If you get one of those super-powerful rare earth magnets and drop it down a pipe made from copper or some other non-ferrous metal, it will fall in bizarre slow motion - because the motion of the magnet generates a current, and the current generates a magnetic field that resists the motion of the magnet. Or in energy budget terms, kinetic energy is extracted from the magnet (thrown away as heat as the current circulates in the metal) - because energy of the magnet’s motion has been taken away, the magnet moves more slowly. So can this be used for free levitation? No - it can’t. The magnet falls, inducing a current that creates a magnetic field that slows its fall, but as its fall is slowed, it induces less current, so the resistance to its descent is reduced. If it induced enough current to arrest its own motion, that lack of motion would also switch off the force supporting it. But the point is still this: You can’t spend the same money twice - in any energy transaction - even in a theoretically perfect and lossless system - a increase of energy in one place means a balancing decrease somewhere else. ---
**Author:** ![komolono](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/komolono/32/532_2.png) [@komolono](https://boards.straightdope.com/u/komolono)\ **Post date:** [April 19, 2010, 10:46am UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/109 "2010-04-19T10:46:52Z")
> [@Mangetout](#): > > That’s why a bicycle with dynamo-powered lights is noticeably harder to pedal when you switch the lights on. Back to the original propeller powered apparatus - will it stop? I’m still puzzeled by the problematics of how big the vessel (that is the stator magnet) can be. Still to make it buoyant would be a difference of one or two moles… ---
**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:** [April 19, 2010, 10:59am UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/110 "2010-04-19T10:59:27Z")
> [@katunari](#): > > Back to the original propeller powered apparatus - will it stop? No idea, but there’s an absolute limit to the amount of energy you can extract from the motion of its descent. > [@](#): > > …Still to make it buoyant would be a difference of one or two moles… Making it buoyant is a problem of displacing water at enormous pressure, which is hard work. If you make your sub nearly-buoyant, then it won’t sink very fast and you won’t generate much on the way down. If you make it very sinky, you’ll harvest more energy from its descent, but it will be much harder work rendering it buoyant at the bottom. You can’t win. ---
**Author:** ![komolono](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/komolono/32/532_2.png) [@komolono](https://boards.straightdope.com/u/komolono)\ **Post date:** [April 19, 2010, 11:05am UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/111 "2010-04-19T11:05:14Z")
> [@Mangetout](#): > > If you make your sub nearly-buoyant, then it won’t sink very fast and you won’t generate much on the way down. I thought that the speed would not be an issue - gravity’s effect regardless of their mass… Thats why I made it a javelin in the first place. ---
**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:** [April 19, 2010, 12:04pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/112 "2010-04-19T12:04:55Z")
> [@katunari](#): > > I thought that the speed would not be an issue - gravity’s effect regardless of their mass… > Thats why I made it a javelin in the first place. The bigger/more massive something is, the more work it can do as it falls. That’s why waterwheels are big and it’s also why swimming while wearing a wristwatch is OK, but swimming with an anvil tucked into your shorts is difficult. If your sub is nearly buoyant, it will sink _gently_ through the water, so your propellers/turbines will just slow it down to a near standstill. If it’s really heavy and non-buoyant, it will sink _forcefully_ through the water, making it more (although still not ver) profitable for your turbines, but making it difficult to bring back up again. You can’t win. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [April 19, 2010, 12:10pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/113 "2010-04-19T12:10:38Z")
> [@katunari](#): > > I thought that the speed would not be an issue - gravity’s effect regardless of their mass… > Thats why I made it a javelin in the first place. The javelin shape just reduces the drag from the water. Hydrodynamic drag is an energy loss, so by reshaping your sub, you’re making it easier to recover energy with your propeller. That’s good, but it doesn’t create any new energy. This is what I meant by accounting for energy flow–minimizing energy waste does not get you free energy. ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [April 19, 2010, 1:12pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/114 "2010-04-19T13:12:14Z")
Addendum to Post #84. From ancient times an untold number of attempts have been made to achieve perpetual motion without success. Continue to waste time and effort on any PM scheme and your name will be just another individual searching for a willow-the-wisp. Note that doing the same thing over and over is classed as stupidity or incompentance. ---
**Author:** ![komolono](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/komolono/32/532_2.png) [@komolono](https://boards.straightdope.com/u/komolono)\ **Post date:** [April 19, 2010, 1:37pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/115 "2010-04-19T13:37:44Z")
> [@spingears](#): > > Addendum to Post #84. > > From ancient times… From ancient times they tried to fly also. What is your point - that this board is only for professionals who have nothing to learn? ---
**Author:** ![ivan\_astikov](https://avatars.discourse-cdn.com/v4/letter/i/58f4c7/32.png) [@ivan\_astikov](https://boards.straightdope.com/u/ivan_astikov)\ **Post date:** [April 19, 2010, 1:43pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/116 "2010-04-19T13:43:29Z")
I suppose you’ll say there are flaws in [this design](http://i186.photobucket.com/albums/x171/CJOKUSAP/plane.jpg) also? ---
**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:** [April 19, 2010, 1:50pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/117 "2010-04-19T13:50:10Z")
Flying was never impossible - we just didn’t know it was possible. Considering flight impossible was ignorance. The laws of thermodynamics are not statements of our ignorance about the universe - they are the sumnation of our _knowledge_. So us thinking you can’t create energy out of nothing _ **is not comparable to** _ the ancients thinking flight was impossible. And even if it were comparable, the fact that one problem was overcome does not mean a different one can be. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [April 19, 2010, 1:58pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/118 "2010-04-19T13:58:05Z")
> [@katunari](#): > > From ancient times they tried to fly also. > > What is your point - that this board is only for professionals who have nothing to learn? I think his point is that you don’t seem to be learning the lessons that are being offered. People are not pointing out that these things are **difficult** due to limits of currently available technology; if that were the case - like trying to fly - then you could be optimistic about future technology making these things possible. What people are pointing out is that the things you propose are, according to the laws of thermodynamics, **impossible**. Even if you invent miracle technologies that can make processes 100% efficient, it will **never** be possible to extract energy indefinitely from a closed system. ---
**Author:** ![Sapo](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@Sapo](https://boards.straightdope.com/u/Sapo)\ **Post date:** [April 19, 2010, 2:02pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/119 "2010-04-19T14:02:21Z")
> [@Mangetout](#): > > … swimming with an anvil tucked into your shorts is difficult… Is that an anvil in your shorts or are you just drowning to see me? ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [April 19, 2010, 2:03pm UTC](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037/120 "2010-04-19T14:03:40Z")
it can be good to let your mind wander and be creative. with a good background it can produce good results some times, even often. without a good background it can be a time waster or at least a slow way to learn. to learn physics in order to do correct calculations you would need calculus. to use physics in daily life, mathematics at a level from 12 years of school (high school in USA) would be sufficient. there are plenty of good books to learn physics with out lots of mathematics. you could try a book that rather than learning from just principles looks a physics in everyday life; Flying Circus of Physics is a popular one. learning some physics can help you do things easier in life and not injure yourself or others. i’ve never met a science i didn’t like. i’ve never met a science i wasn’t amazed by. i’ll learn science for fun as well a practical use. every science i’ve learned some of i’ve used for a practical purpose in my life as well. [Previous page](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037.md?page=5) [Next page](https://boards.straightdope.com/t/perpetual-motion-is-it-so-damn-hard/536037.md?page=7)