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Topic: Gravitational Potential Energy  (Read 4511 times)

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Offline zeoblade

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Gravitational Potential Energy
« on: September 29, 2011, 03:10:43 AM »
I want to propose that Gravitational Potential Energy (GPE) is a renewable energy input source but I feel maybe GPE might not be accepted as part of the surroundings acting upon the energy boundary of a system.

What are the rules of the energy boundary that umpire what is allowed and disallowed? If you know a reliable textbook or article, please let me know

Offline fledarmus

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Re: Gravitational Potential Energy
« Reply #1 on: September 29, 2011, 07:48:07 AM »
Isn't that what hydroelectric power is? Converting the gravitational potential energy of water into electricity?

Offline zeoblade

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Re: Gravitational Potential Energy
« Reply #2 on: September 29, 2011, 08:16:23 AM »
the energy input for hydroelectric power is according to the hydrological cycle. a lot of people say that the sun is the energy input that evaporates water into atmosphere for re-deposition by rain behind the dam

however, i feel that there is contribution from both the sun and GPE. the sun evaporates the water by providing the heat energy but the water does not displace by heat alone. the fluid density decreases as it changes from liquid to vapour. as the density decreases, the weight force of the vapour is less than the surrounding atmosphere. so the GPE of the surroundings is exhausted to displace the water vapour higher into the atmosphere. high in the atmosphere it transfers its heat, cooling and condensing as rain behind the dam

i really want to say GPE input for another example but i have been instructed to not say GPE. surely there must be some energy boundary rules. i want to say GPE is the surroundings acting upon my system of interest

Offline Borek

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Re: Gravitational Potential Energy
« Reply #3 on: September 29, 2011, 09:19:08 AM »
the GPE of the surroundings is exhausted

It is not. Water is transported by motion of the atmosphere, the energy source behind is the Sun. Yes, it goes up because its density decreases, but its density decreases because of the temperature change.
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Offline zeoblade

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Re: Gravitational Potential Energy
« Reply #4 on: September 29, 2011, 03:58:56 PM »
It is not. Water is transported by motion of the atmosphere, the energy source behind is the Sun. Yes, it goes up because its density decreases, but its density decreases because of the temperature change.

i beg your pardon, my response was unclear

the mass of water of given GPE changed to KE and thus to electricity has energy input by the sun

once the phase change occurs from liquid to solid, the same mass of water occupies a larger volume. the density has decreased

due to decrease in density, the an equivalent volume of atmosphere displaces that volume of water vapour into the atmosphere by exhausting GPE of that equivalent atmosphere volume

why does it the equivalent volume of atmosphere displace the water vapour? because there is a weight force of the atmosphere defined by the mass of that atmosphere volume accelerated by gravity. this force is greater and seeks to get under the water vapour's weight force thereby displacing it

so the GPE of the displacing atmosphere volume is exhausted to raise the water vapourised by the sun

this is my flow of logic, i beg your criticism

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