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greendoor
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Posted: Sat Jan 29, 2011 5:57 am Post subject: re: Definition of "Gravity is conservative" ? |
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Conservation applies to things which are in short supply and need to be conserved.
People compare gravity to a spring, and claim that you can only get out of it what you put into it. This is a very closed mind view, which I hope I can demolish with the following ...
Slingshot effect. http://en.wikipedia.org/wiki/Gravity_assist
Space craft can use the free energy of gravitational attraction to greatly reduce their fuel requirement.
This proves that gravity can be used as an energy source - a fuel if you will. The space craft are benefiting from "getting out" energy which they did not have to "put in".
Period.
Those totally committed to being a know-it-all skeptic will try to argue that this is simply removing energy from the planet, and the planet rotation will slow down slightly - or whatever theory helps to quell the panic arising in their chest. All utter bollocks, probably. This presupposes that we know exactly what gravity is and what causes it. Which we don't.
We don't need to know how gravity works to make earth-based machines - just that there is a downwards force vector acting on all mass.
To those who argue that gravity acts like a spring, and say "we can only get out what we put in" - I would say that is only one way in which we can use it. The slingshot effect is another way, where obviously we can get out much more than what we put in. And I believe there are earth-based ways of extracting free energy from gravity.
Think about a river with a steady flow of water. Insert a bucket on a rope into this stream. We experience a Force vector acting on the rope. Can we use this Force to perform useful Work? Yes - but as the bucket gets pulled downstream, we end up having to reel the bucket back in again. To do this, we have to apply an equal and opposite Force for the same amount of Time. So do we give up and say that a flowing river is Conservative - we can only get out what we put in?
Well if we insist on doing it this way - yes, we can't can't get out any more than what we put in. It is acting like a spring.
With the benefit of hindsight, we all know that we can make a waterwheel and extract real useful work from a flowing river. But imagine if we had never invented the water wheel, and still didn't know how to get power out of flowing water ...
With a water wheel (or wind mill) we have to cycle our machine to get energy from the water flowing downstream, but then return the working part of our machine upstream but somehow using less energy than what we obtained going downstream. This makes the process less efficient, because the available power is the difference between the gain and the loss. But since the flowing stream is free and continuously available, we don't care.
So maybe - just maybe - gravity is like that flowing stream. Yes - we can choose to use it like a spring, and only take what we put into it. But maybe we find a way to return a mass with less energy than what we can obtain out of it's fall.
Science has a history of armchair experts proclaiming the impossibility of certain things. It doesn't stop some people from just going ahead and building stuff that works.
_________________ Anything not related to elephants is irrelephant.
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rlortie

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ovyyus

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nicbordeaux
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Posted: Sat Jan 29, 2011 12:08 pm Post subject: Re: re: Definition of "Gravity is conservative" ? |
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| rlortie wrote: | greendoor,
| Quote: | | Think about a river with a steady flow of water. Insert a bucket on a rope into this stream. We experience a Force vector acting on the rope. Can we use this Force to perform useful Work? Yes - but as the bucket gets pulled downstream, we end up having to reel the bucket back in again. To do this, we have to apply an equal and opposite Force for the same amount of Time. So do we give up and say that a flowing river is Conservative - we can only get out what we put in? |
As I pointed on on another thread, we have all gone along with the notion that an equal and opposite force (I will leave time out of this) must be applied to return the bucket upstream.
This is my problem; An equal applied force will only stop the bucket from traveling downstream, that is to say you have equaled and or canceled. It will take more force to return it upstream. This of course also holds true to my thinking of gravity.
Would you care to give your opinion on this, I would really like to hear some input.
Ralph |
Equal forces or more force required to move upstream in the flowing water analogy, there is the other case : lateral thinking. If you design your bucket so that at the end of "x" distance travelled via the force of water flow it rises to the surface and you can reverse it so it empties under gravity, you can then with a nicely designed bucket apply a bit of rewind force on it's rope to skip it over the surface. The net result is a positive for you. No physics laws blown apart, just good mechanical trick.
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ruggerodk
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