# Perpetual Motion Compressed Air Engine? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [October 14, 2008, 4:29pm UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719 "2008-10-14T16:29:54Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![larry054](https://avatars.discourse-cdn.com/v4/letter/l/3ab097/32.png) [@larry054](https://community.cartalk.com/u/larry054)\ **Post date:** [October 15, 2008, 3:17pm UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/21 "2008-10-15T15:17:31Z")
That’s nothing! I saw a video on [MSNBC.COM](http://MSNBC.COM) a couple months ago demonstrating a car that runs on ordinary water! I wrote to the MSNBC science editor twice imploring them to take that ridiculous video off their web site. They finally did take it off, only because they needed to make room for something equally stupid — or ---- maybe it was a cover up by “Big Oil.” All depends on your point of view. ---
**Author:** ![B.L.E](https://avatars.discourse-cdn.com/v4/letter/b/848f3c/32.png) [@B.L.E](https://community.cartalk.com/u/B.L.E)\ **Post date:** [October 16, 2008, 12:36am UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/22 "2008-10-16T00:36:04Z")
Perpetual motion? Escher had that figured out years ago. [![](http://i170.photobucket.com/albums/u260/ben_eberle/waterfall.jpg) ](http://i170.photobucket.com/albums/u260/ben_eberle/waterfall.jpg) ---
**Author:** ![Manolito](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/manolito/32/3070_2.png) [@Manolito](https://community.cartalk.com/u/Manolito)\ **Post date:** [October 16, 2008, 4:43am UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/23 "2008-10-16T04:43:52Z")
You can run a car on water - if you throw some calcium carbide in the tank before you ‘gas it up’ with water. CaC2 + 2 H2O =\> C2H2 + Ca(OH)2 You probably did this in high school chemistry class. It is the formula for acetylene made from water and calcium carbide. As near as I can figure, the cost would be roughly equivalent to $100/gallon gasoline. Sounds pricey, but it is a rich source of revenue for scam artists looking for ‘investors’ who think they can get rich by investing in a water-powered car. ---
**Author:** ![mr\_josh](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mr_josh/32/3008_2.png) [@mr\_josh](https://community.cartalk.com/u/mr_josh)\ **Post date:** [October 16, 2008, 4:56am UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/24 "2008-10-16T04:56:31Z")
We all know that Isaac Newton worked for Exxon-Mobile. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [October 16, 2008, 1:40pm UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/25 "2008-10-16T13:40:45Z")
This is what they did 100 years ago to generate the acetylene for the headlights on those old cars. ---
**Author:** ![rdavidmayo](https://avatars.discourse-cdn.com/v4/letter/r/59ef9b/32.png) [@rdavidmayo](https://community.cartalk.com/u/rdavidmayo)\ **Post date:** [October 17, 2008, 5:22pm UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/26 "2008-10-17T17:22:19Z")
He seemed to think that each wheel would have a compressor that would recharge the air tank. I tried to explain the concepts of efficiency, drag, etc, and that you can’t get more out of a process than you put into it unless you are splitting atoms, but he still insisted that it was possible and, in fact, had already been built. Truth is that they have been built but it requires periodic recharging of the air tanks and has very limited range and speed. There are electric cars that do better and all you have to do is plug them in to an electrical source, instead of looking around for a high-pressure air compressor. ---
**Author:** ![hwertz](https://avatars.discourse-cdn.com/v4/letter/h/779978/32.png) [@hwertz](https://community.cartalk.com/u/hwertz)\ **Post date:** [October 19, 2008, 2:04am UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/27 "2008-10-19T02:04:02Z")
``` A French company had developed a compressed air car. Tata (an Indian conglomerate who makes cars among many other things) had either licensed or bought outright the design, and from what I'd read it may even be on the market now. But, it's DEFINITELY not a perpetual motion device -- it relies on hooking it up to an air compressor to recharge the compressed air. Possibly it can regenerate, pumping a little air back in when braking or slowing down... but that is not going to even approach breaking even (and, really, is no different than the regenerative braking on electric or hybrid cars, which noone would claim makes them perpetual motion machines.) ``` ---
**Author:** ![bentley](https://avatars.discourse-cdn.com/v4/letter/b/b9bd4f/32.png) [@bentley](https://community.cartalk.com/u/bentley)\ **Post date:** [October 20, 2008, 5:12pm UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/28 "2008-10-20T17:12:14Z")
Hi all, There is a “Stirling engine” that runs on temp’ changes, I have seen one running and it looks like perpetual motion. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [October 20, 2008, 5:35pm UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/29 "2008-10-20T17:35:13Z")
Not quite - you have to have an energy source to generate the temp changes. Here’s a good short explanation in Wikipedia. Note that you have to have a hot and a cold side. > **[Stirling engine](https://en.wikipedia.org/wiki/Stirling_engine)** > > A Stirling engine is a heat engine that is operated by a cyclic compression and expansion of air or other gas (the working fluid) at different temperatures, such that there is a net conversion of heat energy to mechanical work. More specifically, the Stirling engine is a closed-cycle regenerative heat engine with a permanently gaseous working fluid. Closed-cycle, in this context, means a thermodynamic system in which the working fluid is permanently contained within the system, and regenera Origi... ---
**Author:** ![deckhole](https://avatars.discourse-cdn.com/v4/letter/d/ea5d25/32.png) [@deckhole](https://community.cartalk.com/u/deckhole)\ **Post date:** [October 20, 2008, 5:45pm UTC](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719/30 "2008-10-20T17:45:55Z")
You seem to already know the answer. No truth to it. While there are multiple ways to “get back” **some** typically wasted energy (Counter-Electro-Moto-Force Braking, compressed-air recharge while braking or going down hill.) You always lose some to the 2nd Law going into 1 of the 2 directions and 99.9999% of the time you lose in both directions (making exceptions to super-fluids, super-conductors, 0K situations, etc.) You can have self-charging/fueling/compressing vehicles during braking or going downhill, etc. etc… But there is always a loss so you don’t get it all back. 49% would be pretty remarkable and 100% impossible. [Previous page](https://community.cartalk.com/t/perpetual-motion-compressed-air-engine/20719.md?page=1)