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So I was busy trying to solve the world's problems the other day and a thought crossed my mind. I came across some data about cars that run on H2O and I was thinking that this seems like a great way to get the world off oil. Granted there are many considerations (the biggest environmental impact analysis ever) that must be accounted for. It seems to me that water provides a pretty good source. I read that it's even more efficient than the standard petroleum based fuel. If this is the case, than why don't we see more of it. The developed world would love to end its nasty little addiction to the oil, right? So why have we not seen more of these cars.

I apologize if this all sounds dumb, I am just curious. So I guess my big question is can we efficiently run cars on H2O? If so, what is the mechanism creating the necessary thrust. I imagine it's the H part of the compound. I might have already answered my question. Are cars that run on H20 safe? I know some people have developed hydrogen fueled cars, but they require a fuel tank that's more secure than the black box found on an airplane. I can see the big argument here being that we all need the water to drink. I thought this too, the first time the subject came to mind, but consider the fact that the oceans are nothing more than a big trash can. Seriously, humans don't get their drinking water from here and all the nasty stuff from the land eventually makes its way down into these bodies. Additionally, we might be able to make some more land for everybody and the oceans are full of undiscovered resources like gold and other metals. Again, I am no expert, but it just seems like the solution is staring mankind in the face. Any input would be greatly appreciated.

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closed as off-topic by ACuriousMind, tpg2114, CuriousOne, Gert, Emilio Pisanty Mar 30 '16 at 3:11

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question appears to be about engineering, which is the application of scientific knowledge to construct a solution to solve a specific problem. As such, it is off topic for this site, which deals with the science, whether theoretical or experimental, of how the natural world works. For more information, see this meta post." – ACuriousMind, tpg2114, CuriousOne, Gert
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  • $\begingroup$ You want to put steam engines into cars? That's a very old idea that never really caught on. "Firing up" the engine literally takes half an hour or so and boiler explosions are nasty. $\endgroup$ – CuriousOne Mar 30 '16 at 0:37
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    $\begingroup$ @CuriousOne I thought it was more about something like a water fuel-cell -- split it into hydrogen and oxygen with a battery or something, burn both and get energy out with only water as the product. Not that it's any less misguided than steam engines of course... $\endgroup$ – tpg2114 Mar 30 '16 at 1:07
  • $\begingroup$ I do not want to demotivate you, however, your question would have been better suited at skeptics.SE. Also, using water as fuel violates the laws of physics. One report was given here $\endgroup$ – Janus Boffin Mar 30 '16 at 1:16
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    $\begingroup$ @tpg2114: A properly designed Rube Goldberg machines involves a squirrel, goat or other small animal as part of the design. Fortunately, such designs won't pass animal cruelty regulations anymore... $\endgroup$ – CuriousOne Mar 30 '16 at 1:19
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    $\begingroup$ I'm not sure whether this comment will be visible to anyone, so maybe here is a good place to say this: I think this question has no merit whatsoever and should be banished to oblivion. $\endgroup$ – Emilio Pisanty Mar 30 '16 at 3:11
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To follow up on user289661's excellent answer.

You can think of water as burnt Hydrogen. The Hydrogen fuel has already burnt to create water some time in the distant past - releasing energy. You can split water back into hydrogen and oxygen and burn it again - but that would obviously take the same energy to split it as you get burning it, less any efficiency losses.

What you are saying is, effectively, why can't we capture the exhaust from a car and use it to run the car !

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I am sorry to sound discouraging, but you do not seem to be familiar with some of the common sense of physics, namely, the conservation of energy.

The conservation of energy states that among a closed group of systems, (which you can understand as a room that is shut in every way so nothing can get in or out) energy is conserved.

If you try to put water as a fuel into cars, you are effectively trying to get energy stored in the water molecules and put them into the car so the car gains kinetic energy and start moving. This will require water to become some other substance that has a lower amount of stored energy than it started with, which is very unlikely, because we are yet to discover any substance that can be chemically derived from water and has a lower chemical potential energy.

You can try to use nuclear fusion to get energy from the hydrogen atoms in water, but there are no effective nuclear fusion reactors in the world yet, and much less so ones that can be produced cheaply and installed in cars.

I appreciate your attention to global issues and interest in physics, but I would recommend some more basic studying before attempting at tricky problems like the one you posted

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One of the great things about the internet is that you can find the most amazing facts on it - and some of them are even true. Cars which run on water, I'm afraid, are a classic case of facts which, alas, are not true. The idea is incredibly attractive, and it keeps popping up, but the folks who make the claims seem consistently (like 100% of the time) unable to back up their claims. Well, there's always the version that goes that the automobile industry has a SWAT team (legal or otherwise) running around suppressing the invention. You might give a bit of thought as to just how powerful the auto industry is these days, and how it could persuade the military not to insist on using the technology.

On a more physicsy note, water is already hydrogen which has been burned. It is, if you will, the ash which results from burning hydrogen. It is pretty trivial to demonstrate that water is also the most stable of the hydrogen/oxygen compounds, and so cannot be made to provide further energy by adding oxygen and trying to burn it. It is not for nothing that water is typically used to extinguish fires - does that suggest that it is a potential fuel?

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