Thread: Concervation of Energy

OK, I know this can't work, but I'm not sure of the exact reasons it would fail.
So, basically the question is, if i have water pumped to the top of a long ramp which is filled with water wheels that it turns as it comes back to earth, why wouldn't it produce more electricity than it used to pump the water.

Again, I know it can't, but yet it seems as if turning fifty waterwheels would produce more electricity than the pump would take.

If i had to guess I would say that the amount of energy the water produces by falling is less than the energy to lift it, but the solution feels unsatisfactory. Perhaps that's just because I am unnecessarily complicating things with multiple water wheels because they would still get the same amount of energy as a single wheel.

Thanks,
Elton

Originally Posted by Torl

OK, I know this can't work, but I'm not sure of the exact reasons it would fail.
So, basically the question is, if i have water pumped to the top of a long ramp which is filled with water wheels that it turns as it comes back to earth, why wouldn't it produce more electricity than it used to pump the water.

Again, I know it can't, but yet it seems as if turning fifty waterwheels would produce more electricity than the pump would take.

If i had to guess I would say that the amount of energy the water produces by falling is less than the energy to lift it, but the solution feels unsatisfactory. Perhaps that's just because I am unnecessarily complicating things with multiple water wheels because they would still get the same amount of energy as a single wheel.

Thanks,
Elton

Put simply: As the water hits each water wheel, it is slowed up by the amount of energy it gives up to the water wheel. Thus when it hits the next wheel, it is moving slower than it would have been if it hadn't struck the first wheel. Thus, it has less energy to give to the second wheel. this wheel also removes energy. This continues down the line.

If you have just one water wheel at the bottom of the ramp, then the water isn't slowed as it falls and is moving very fast when in hits the wheel and has lot's of energy to give the wheel. So, with one wheel, it gets all the energy of the falling water, and with many wheels the energy is spread out among all the wheels.

As you raise water (or any oher object) you will be investing potential energy, the higher you raise it the more potential energy it will possess, as the water falls or returns to it's starting point it gives up this energy. The only amount of energy you can recover is the amount put in. Some of the energy in any mechanical system is lost through friction thus the 'usuable' energy recovered will always be less than the invested energy.

When James Joule, the scientist for whom the unit of energy is named, went on honeymoon he took with him - in addition to his bride - an accurate thermometer. He spent time taking the water temperature at the top and the bottom of waterfalls, looking for an increase in temperature that would reflect the frictional losses wert referred to.