Give gravity time to act.

[Georg Künstler]

Give gravity time to act.

To my sentence give gravity time to act, I have made a drawing.

Assume we have a river. The high difference between start and end should be 10 meter. The distance between start and end should be 10000 meter. Now we can measure the speed of the river at the endpoint, and we can calculate the energy. This is an easy task.

Now we put a water-wheel in the water, near to the start point. The wheel will turn, we can extract energy. Does this extraction lower the speed at the endpoint ? I think not.

Even if we put n-wheels in the river, the speed at the endpoint will be the same.

Only when we put a wheel directly at the endpoint, we get a lower speed.

So if you donÂ’t overstress the Gravityforce, it recreates the speed of the water again and again.

So gravity needs Time to act.

Best regards

Georg

[Jonathan]

Now we put a water-wheel in the water, near to the start point. The wheel will turn, we can extract energy. Does this extraction lower the speed at the endpoint ? I think not.

I think so. If the water falls through ten meters, it will have a velocity of 14m/s (=sqrt(2g10))at the end. If at the exact point where the water has fallen one meter we place a water wheel and extract the water's complete kinetic energy at that point, the water at the end will have a velocity of 13.3m/s (=sqrt(2g9)). In this case, the simplest, and most materially cost efficient, thing to do is to put one water wheel at the end, and take all the energy at once, instead of having stages gradually take the energy.

[Georg Künstler]

and that exact is the problem, saving material cost, and most effectiv.

I think that the end of the river does't know(is not aware) that a waterwheel has extracted energy 100, 200, 300 m before. The speed at the end will still be the same. Gravity has subtituted.

The sum of the gradually taken energy is greater than m*g*h.

Best regards

Georg

[Jonathan]

I don't think so, merely because it doesn't make any sense. But of course I don't have a river in my backyard to experiment with, so though I know you're wrong on this, I technically can't prove it.

[AlanR]

My 2c worth...

What about terminal velocity? eg, an object falling accelerates under G to reach a certain terminal velocity (air friction balances G). You could then "extract" energy (do work) and velocity would fall below terminal. Then G would accelerate it back to terminal velocity.
I think the same thing is happening with the river example, in a way.
Speed of river remains constant at all points (assuming cross-sectional dimensions are constant, of course) G cant make it go any faster, due to balanced forces. So why not draw some KE from the rivers motion, the rivers slows a little, as G then brings it back to its former "terminal" velocity?
Maybe its actually very complex, with all the interactions, hydrodynamic principles, etc which I am certainly not qualified to reply confidently.

[Jonathan]

I was talking to my dad and he said the same thing, and I came here to point it out, and say why it was trivial. The first is done, so it is trivial because having a terminal velocity in our example doesn't do anything but make the situation more complex and less efficient. If the water reaches terminal velocity after a one meter fall, it's terminal velocity will be 4.4m/s (=sqrt(2g)). If we then place a water wheel at that point and remove all the energy, it's velocity at the end of the ten meter total height change will indeed be the same as if the wheel wasn't there, 4.4m/s. But in this case, we are not getting as much energy as we would with one wheel at the end of the original. So to get the same energy out that the original example had, we'd have to put a water wheel in for every one meter fall. At this point we have matched the energy output of the original, but we've now used ten wheels and I garantee that one will find that adding more than those ten wheels at one meter height distances will add no more energy, it will only spread the existing amount thinner amoung them. So we see that in fact, though this does more correctly conform to Georg's example, it is actually less efficient.

[Georg Künstler]

It is less efficiant if you take the energy in one portion. We have a water power station by Rheinfleden, which produces more energy than only m*g*h. It uses the speed of the river. And the speed was created from gravity not from m*g*h. The river is not 10 m long. No he is 10 000 m in my example. At the end of 10 000 m the river doesn't know, that a waterwheel was put into the river after 2 m from the beginning, and has extracted energy.
The river speed is the same. There was only for a short time a disturbance of his flow.


Best regards

Georg

[Jonathan]

You misunderstood, I wasn't meausring horizontally, I was measuring in vertical increments. Georg, you do not understand the equation, mgh gives you the energy, sqrt(2gh) gives you the velocity. The water does know that there is a water wheel upstream.
However, you are correct that one can get more energy out than mgh, by restricting the water's path and making it spiral, just like Victor S. did. The physics of that though are well understood, the engineers are just stupid not to use it. But that is not what we were talking about.

[iacob alex]

Hi Georg!Searching in the "history" of this forum(I am a newbe here...),I discovered your subject "Give gravity time to act"/01.06.04 .This can be the "key point",to develop statics into dynamics in a potential field(but a real material flow...).De facto,an intended unbalanced wheel(many first class levers with a common fulcrum,so arranged to have an long arm-short arm configuration vis-a-vis a vertical line) has as a mechanical equivalence a single stable lever(two unequal arms /very large overturned V shape,under the fulcrum ...so a stable position ,with the CoG on vertical line,below the supporting point).At this "point" any dynamics is "buried":an unbalanced wheel(any!) becomes alike a static "weighing machine",no more than a stable balance,just a little swinging up and down face to the horizontal line.As you said:"gravity needs time to act".Then ,why a wheel and not a single unbalanced lever ?So wheel vs. lever can be developed into a statics vs. dynamics problem.Between a stable balance/wheel concept(two equally opposed torques~statics) and a pendulum(one torque only~dynamics) it's a huge world of pendular levers/lever concept(two unequally torques~dynamics) possible configurations in gravity ready to be "set free".A fall needs time to be manifested as a "vis viva".Gravity manifests gradually:it asks for time,as you noticed.The "self" problem is the next one.All the Bests!/Alex

[Gravmaster2000]

Georg, I agree with your water wheel example, the trick is finding the minimum distance required so one water wheel does not 'see' the one above. It is friction that keeps the water flowing slow enough to do this....if you had a series of dams in a river, as long as the outlet ports are JUST above the water level, whether there is a dam downstream or not, it will not SEE it.
I have thought about "for every action there is a reaction" statment as well-the interpretation of that statement changes a lot with scale. For example,you have a fan blowing air in a room, its base is actually trying to push the whole house in the opposite direction! If the fan is in a small box, the air pressure on the front side cancels this motion out-does this happen in a really big room too? Scale is important, here. Could a helicopter lift a building from the inside if it was REALLY big?!
You know, and ideal wheel would be one that accelerates its weights up to the terminal velocity...more time is wasted after that. That would be one BIG wheel!!!

[iacob alex]

.....it's an old topic (started by Georg Kunstler,2006).

His dilemma was:to take energy(from gravity fall/flow of a liquid body/river) at once or gradually.

In a manner,it's alike another dilemma:"Wheel vs. lever..."(see this topic),if we use the fall of a solid state body.

So,we can gather power "step by step" or as an "avalanche"...here is a great difference!

All the best! / Alex

[iacob alex]

.....or simply ...to work,so to develop self motion in a continuous unbalanced configuration.
A single mass , if allowed to fall freely , "speeds" the distance ( and work ...) proportional to the square of the elapsed time , as follows :
https://upload.wikimedia.org/wikipedia/ ... g_ball.jpg
We can take advantage of this increasing non-linear "stream" of "free" kinetic energy and develop self motion in a simple unbalanced leverage of no more than two masses.
Al_ex