navigator Posted May 31, 2009 Author Share Posted May 31, 2009 But their kinetic energy wont be the same in the bottom reservoir... That is the important bit. Merged post follows: Consecutive posts merged I understand that, but do you understand that this is a result of the height of the fall and not the work the kinetic energy does. The potential energy is less at the bottom resevoir, but it is always equal regardless of how much work it does on the way down. The energy goes as follows for a dam: With the turbine in place: [in the top reservoir] Gravitational potential energy (GPE) -> [just before the turbine] Kinetic energy (KE) (before turbine) + less GPE -> [just after the turbine] KE of the turbine ('mechanical energy') + less KE (after turbine) + less GPE -> [hitting the bottom reservoir] energy produced by turbine + a bit more KE + a bit less GPE -> [in the bottom reservoir] alot less KE + noise energy (KE) + temp change (KE) + the same GPE + the energy created by the turbine With the turbine removed: [in the top reservoir] Gravitational potential energy (GPE) -> [just before the turbine] Kinetic energy (KE) (before turbine) + less GPE -> [just after the turbine] a tiny bit more KE + a tiny bit less GPE -> [hitting the bottom reservoir]a bit more KE + a bit less GPE -> [in the bottom reservoir] alot less KE + noise energy (KE) + temp change (KE) + the same GPE So there is less KE removed from the water system in the second situation, the total energy of the whole system is conserved, but in the first set up some KE is removed resulting in the water moving at a slower velocity when it hits the final reservoir. Why can't you just tell me what form of energy your reffering to when you describe what happens when it goes from potential to kinetic and back to potential? Link to comment Share on other sites More sharing options...
Klaynos Posted May 31, 2009 Share Posted May 31, 2009 I understand that, but do you understand that this is a result of the height of the fall and not the work the kinetic energy does. The potential energy is less at the bottom resevoir, but it is always equal regardless of how much work it does on the way down. The total energy remains the same. With no turbine both streams would have the same KE at the bottom which is directly related to the height of the fall. With a turbine in one stream the KE at the bottom will be different, but the change in PE would still be the same as some of the KE has been removed, it was converted into spinning the turbine... Why can't you just tell me what form of energy your reffering to when you describe what happens when it goes from potential to kinetic and back to potential? The type of energy is kinetic and potential energy. If you drop a ball it has some potential at the top and that changes to kinetic energy as it falls. Link to comment Share on other sites More sharing options...
navigator Posted May 31, 2009 Author Share Posted May 31, 2009 The total energy remains the same. Disagree. When the water reaches the bottom resevoirs the system with the turbine will have stored energy the system without the turbine did not. Therefore the potentials at the bottom are different, although the difference is found in a different form of energy, but the potential energy in the water at bottom resevoirs is still equal. With no turbine both streams would have the same KE at the bottom which is directly related to the height of the fall. Agree With a turbine in one stream the KE at the bottom will be different, the change in PE would still be the same as some of the KE has been removed but it was converted into spinning the turbine..., Do you not see the contradiction in the bolded part? If KE has been removed in order to convert its force to spinning the turbine, how can the potential at the bottom be the same as the system without the turbine? The type of energy is kinetic and potential energy. If you drop a ball it has some potential at the top and that changes to kinetic energy as it falls. Trust me, I get that part. What I find perplexing is you seem to be unable to tell me what form of energy you are referring to, although you can give many different eloquent eqations to explain what happens when that form of energy goes from one state to the other, potential to kenetic and back to potential. Link to comment Share on other sites More sharing options...
Klaynos Posted May 31, 2009 Share Posted May 31, 2009 Disagree. Whether you disagree or not, that is the physical reality. When the water reaches the bottom resevoirs the system with the turbine will have stored energy the system without the turbine did not. Therefore the potentials at the bottom are different, although the difference is found in a different form of energy, but the potential energy in the water at bottom resevoirs is still equal. I'm not sure if you are confusing something or are completely misunderstanding classical mechanics. The total energy, must remain the same. final KE + final PE + energy generated by the turbine = starting PE With the turbine not there the energy generated by the turbine is just 0, and the kinetic energy in increased as the final PE is a fixed part of the system. Agree Do you not see the contradiction in the bolded part? If KE has been removed in order to convert its force to spinning the turbine, how can the potential at the bottom be the same as the system without the turbine? No, there is no contradiction. The potential is ONLY related to the mass you are considering (which is constant) and the height. Trust me, I get that part. I am not convinced you do. But OK. What I find perplexing is you seem to be unable to tell me what form of energy you are referring to, I told you quite clearly. What do you think the options are here? although you can give many different eloquent eqations to explain what happens when that form of energy goes from one state to the other, potential to kenetic and back to potential. Link to comment Share on other sites More sharing options...
navigator Posted May 31, 2009 Author Share Posted May 31, 2009 (edited) Lets take the experiment one step further. Lets say the distance the water falls is 1100'. Lets also say that water reaches terminal velocity in a 100' fall. the first system has no turbine just water shooting out of the penstock and falling directly into the lower resevoir, 1100'feet below. The second system has 10 turbines, one placed in the path of the water every 100' interval. The system with no turbine starts out as potential energy and then begins to fall. As it speeds up its KE increases until it reaches terminal velocity. At this point the KE in the water is at its maximum and does not increase. It maintains this maximum KE until it reaches the bottom and impacts the lower resevoir. When the water settles in the lower resevoir it has x amount of PE. The system with 10 turbines, the water goes from PE to its maximum KE and then impacts the 1st turbine, which decreases its KE. When it exits the turbine and begins to fall again its KE agian begins to increase until it reaches terminal velocity at which point it impacts the 2nd turbine. This cycle repeats itself 8 more times, the kinetic energy going from a lesser amount to its maximum amount. When the water exits the last turbine it falls a 100' feet again reaching maximum KE just prior to impacting the lower resevoir. Due to terminal velocity, the KE of the water at the bottom of both systems is the same as well as the PE once it settles. The system with the 10 turbines just has much more energy in the form of mechanical energy which could be stored in a battery increasing the overall PE of the system. Just to be clear, the terminal velocity of the water is directly proportianate to the atmospheric pressure, so assuming water reaches terminal velocity in a 100' fall does not invalidate this experiment. Merged post follows: Consecutive posts merged I told you quite clearly. What do you think the options are here? I am beginning to think you do not understand the difference in types of energy, there are only 2 PE and KE, and the forms of energy. from wiki... In the context of physical sciences, several forms of energy have been defined. These include: Thermal energy popularly known as heat Chemical energy Electrical energy Radiant energy commonly known as light energy Nuclear energy Magnetic energy Elastic energy Sound Energy Gravitational energy Which one of these is forms is using its KE to spin the turbine? Merged post follows: Consecutive posts mergedThe fact that wiki lists gravitational energy as form of energy tells me the editors do not understand the definition of convert either. Edited May 31, 2009 by navigator Consecutive posts merged. Link to comment Share on other sites More sharing options...
Klaynos Posted May 31, 2009 Share Posted May 31, 2009 Lets take the experiment one step further. Lets say the distance the water falls is 1100'. Lets also say that water reaches terminal velocity in a 100' fall. the first system has no turbine just water shooting out of the penstock and falling directly into the lower resevoir, 1100'feet below. The second system has 10 turbines, one placed in the path of the water every 100' interval. The system with no turbine starts out as potential energy and then begins to fall. As it speeds up its KE increases until it reaches terminal velocity. At this point the KE in the water is at its maximum and does not increase. It maintains this maximum KE until it reaches the bottom and impacts the lower resevoir. When the water settles in the lower resevoir it has x amount of PE. The system with 10 turbines, the water goes from PE to its maximum KE and then impacts the 1st turbine, which decreases its KE. When it exits the turbine and begins to fall again its KE agian begins to increase until it reaches terminal velocity at which point it impacts the 2nd turbine. This cycle repeats itself 8 more times, the kinetic energy going from a lesser amount to its maximum amount. When the water exits the last turbine it falls a 100' feet again reaching maximum KE just prior to impacting the lower resevoir. Due to terminal velocity, the KE of the water at the bottom of both systems is the same as well as the PE once it settles. The system with the 10 turbines just has much more energy in the form of mechanical energy which could be stored in a battery increasing the overall PE of the system. You are forgetting that the air gains energy from the falling water to maintain terminal velocity. The system with the turbines converts less energy to heat/noise/other losses to the air which is causing terminal velocity. The total energy lost from the system in that case is same in both cases, but with the turbines the loss is useful and retrievable. Just to be clear, the terminal velocity of the water is directly proportianate to the atmospheric pressure, so assuming water reaches terminal velocity in a 100' fall does not invalidate this experiment. Merged post follows: Consecutive posts merged I am beginning to think you do not understand the difference in types of energy, there are only 2 PE and KE, and the forms of energy. from wiki... Which one of these is forms is using its KE to spin the turbine? Merged post follows: Consecutive posts mergedThe fact that wiki lists gravitational energy as form of energy tells me the editors do not understand the definition of convert either. Your list isn't complete. And tbh isn't a good list at all in any way. In mechanics problems there are two types of energy, everything you listed falls into one of them, or is an energy store. Those two froms are KE and PE. Flowing water has kinetic energy, it is moving so it has a velocity and it has a mass, it simply has KE. That KE can be converted into KE of the turbine because the turbine is designed so that if there is pressure applied to it it spins... Merged post follows: Consecutive posts mergedGravitational potential energy, is quite clearly a well understood and known about energy. And has been for hundreds of years. Do you not think that if everyone else agrees on the definition and you disagree with them all then you might be wrong? Link to comment Share on other sites More sharing options...
navigator Posted May 31, 2009 Author Share Posted May 31, 2009 Your list isn't complete. And tbh isn't a good list at all in any way. Thats wikis list, otherwise I agree with you. In mechanics problems there are two types of energy, everything you listed falls into one of them, or is an energy store. Those two froms are KE and PE. Can you provide a reference or link to validate that statement(I understand you meant forms)? Flowing water has kinetic energy, it is moving so it has a velocity and it has a mass, it simply has KE. That KE can be converted into KE of the turbine because the turbine is designed so that if there is pressure applied to it it spins... I quite clearly showed that nothing was converted. The waters KE and PE are equal at the bottom of the two systems, no? Merged post follows: Consecutive posts mergedGravitational potential energy, is quite clearly a well understood and known about energy. Gravity cannot be converted and it is not created, its always there. So how can you classify it as energy and reconcile those two facts with the Law of Energy Conservation? Do you not think that if everyone else agrees on the definition and you disagree with them all then you might be wrong? Absolutely not. But you and everyone else have failed to logically show which form of energy is being converted. Now your back pedaling claiming there is no difference between forms of energy and types of energy. Merged post follows: Consecutive posts merged Your list isn't complete. And tbh isn't a good list at all in any way. Thats wikis list, otherwise I agree with you. In mechanics problems there are two types of energy, everything you listed falls into one of them, or is an energy store. Those two froms are KE and PE. Can you provide a reference or link to validate that statement(I understand you meant forms)? Flowing water has kinetic energy, it is moving so it has a velocity and it has a mass, it simply has KE. That KE can be converted into KE of the turbine because the turbine is designed so that if there is pressure applied to it it spins... I quite clearly showed that nothing was converted. The waters KE and PE are equal at the bottom of the two systems, no? Merged post follows: Consecutive posts mergedGravitational potential energy, is quite clearly a well understood and known about energy. Gravity cannot be converted and it is not created, its always there. So how can you classify it as energy and reconcile those two facts with the Law of Energy Conservation? Do you not think that if everyone else agrees on the definition and you disagree with them all then you might be wrong? Absolutely a possibility. But you and everyone else have failed to logically show which form of energy is being converted. Now your back pedaling claiming there is no difference between forms of energy and types of energy. Link to comment Share on other sites More sharing options...
Klaynos Posted May 31, 2009 Share Posted May 31, 2009 Thats wikis list, otherwise I agree with you. Can you provide a reference or link to validate that statement(I understand you meant forms)? OK, we'll use my favourite formalisation of classical mechanics, legrangian mechanics: http://en.wikipedia.org/wiki/Lagrangian The Lagrangian takes into account the entire energy of the system, it has only two terms kinetic energy and potential energy. Everything falls into one of them. I quite clearly showed that nothing was converted. The waters KE and PE are equal at the bottom of the two systems, no? No you didn't. KE[before] + PE[before] = KE[after] + PE[after] + losses to air resistance[a] KE[before] + PE[before] = KE[after] + PE[after] + losses to air resistance + losses to turbine losses to air resistance[a] > losses to air resistance Infact, we can even say: losses to air resistance[a] = losses to air resistance + losses to air turbine Gravity cannot be converted and it is not created, its always there. So how can you classify it as energy and reconcile those two facts with the Law of Energy Conservation? Gravitational potential energy, not just gravity. Absolutely not. But you and everyone else have failed to logically show which form of energy is being converted. Now your back pedaling claiming there is no difference between forms of energy and types of energy. I'm not back-pedalling. Link to comment Share on other sites More sharing options...
navigator Posted May 31, 2009 Author Share Posted May 31, 2009 OK, we'll use my favourite formalisation of classical mechanics, legrangian mechanics: http://en.wikipedia.org/wiki/Lagrangian The Lagrangian takes into account the entire energy of the system, it has only two terms kinetic energy and potential energy. Everything falls into one of them. In the context of the Lagrangian mechanics described here, the form of energy has no relevance. It is only discussing the types, PE and KE. The Law of energy Conservation uses the term convert to describe what can and cannot happen to PE and KE. In order to calculate the KE and PE in the falling water, we have to have a medium to measure. That has to be the water, because gravity is constant and does not change. The form of energy is very relevant to understanding what is happening in the systems we are discussing. No you didn't. KE[before] + PE[before] = KE[after] + PE[after] + losses to air resistance[a] KE[before] + PE[before] = KE[after] + PE[after] + losses to air resistance + losses to turbine losses to air resistance[a] > losses to air resistance Infact, we can even say: losses to air resistance[a] = losses to air resistance + losses to air turbine In otherwords, the losses due to air resistance in system A are equal to the gains in system B with ten turbines? Maybe so, although, it actually reinforces the reason develop is the correct term, not convert. We have reduced the losses in order to increase the output of the overall system. Thats development, not conversion. Nevertheless, this does not address or name the form of energy that has the KE inside it, which goes directly to the point of this thread. According to the Law of Energy Conservation, some form of energy has to be converted for there to be an increase in PE at the bottom of the systems. Gravitational potential energy, not just gravity. Then there also has to be gravitational KE, no? I'm not back-pedalling. KE and PE are only adjectives used to describe whether the form of energy is in motion or motionless. If KE is being converted it has to have a form or medium to convert from. KE and PE describe the state the energy is in, how can you convert a description of the energy? You cannot establish and validate the thoery that the KE in the water is converted if you cannot even define the form of energy that has the KE. Link to comment Share on other sites More sharing options...
Klaynos Posted May 31, 2009 Share Posted May 31, 2009 In the context of the Lagrangian mechanics described here, the form of energy has no relevance. It is only discussing the types, PE and KE. Types, forms, they have the same effective meaning in this discussion. The Law of energy Conservation uses the term convert to describe what can and cannot happen to PE and KE. The law simply states that the total energy before = total energy after. Total energy = KE + PE in ALL classical formalisations. There are only the two choices, within thouse two there are many different options such as internal energy (temperature), gravitational potential energy, electrical potential energy etc... In order to calculate the KE and PE in the falling water, we have to have a medium to measure. All you need is the position, velocity and mass. In fact the equation of motion and the mass will do. That has to be the water, because gravity is constant and does not change. The gravitational potential does change with height, even the force due to gravity changes with height, but even if you hold that constant you still have a scalar field for the potential energy. The form of energy is very relevant to understanding what is happening in the systems we are discussing. You can consider the KE of each individual water molecule if you want. But it's easier to do it in a macroscopic environment. In otherwords, the losses due to air resistance in system A are equal to the gains in system B with ten turbines? Pretty much. Maybe so, although, it actually reinforces the reason develop is the correct term, not convert. We have reduced the losses in order to increase the output of the overall system. Thats development, not conversion. Convert -> to chagne from one energy to another. Energy is a property of things, you've taken that energy from the water and given it to something else, converted it. The technology to do that is indeed a development. Nevertheless, this does not address or name the form of energy that has the KE inside it, The water simply has linear kinetic energy of the form E = 0.5 mv2 which goes directly to the point of this thread. According to the Law of Energy Conservation, some form of energy has to be converted for there to be an increase in PE at the bottom of the systems. Then there also has to be gravitational KE, no? No, the origin of the KE does not influence it, it has been convereted from GPE to KE. KE and PE are only adjectives used to describe whether the form of energy is in motion or motionless. It is a bit more complicated than that, but that is kinda true. KE tends to have a more specific term, and is often used just for linear KE (see above). If KE is being converted it has to have a form or medium to convert from. Nope. KE and PE describe the state the energy is in, how can you convert a description of the energy? Because the energy changes... You cannot establish and validate the thoery that the KE in the water is converted if you cannot even define the form of energy that has the KE. I'm not sure what you mean by define the form of energy that has the KE... The sentence makes no physical sense. Link to comment Share on other sites More sharing options...
swansont Posted May 31, 2009 Share Posted May 31, 2009 Where does that inreased amount of potential energy, developed by man, fit into the law of energy conservation? Potential energy is work done by a conservative force. Total energy does not change — this is shown by Noether's theorem; conservation of energy is a consequence of physics not changing over time. All the rest is a discussion of semantics of the merits of using "convert," and there's already a consensus. Deal with it. This is a physics board, and the thread is not discussing physics. I don't really see any reason to leave it open. Link to comment Share on other sites More sharing options...
navigator Posted May 31, 2009 Author Share Posted May 31, 2009 Types, forms, they have the same effective meaning in this discussion. In the real world, KE requires a medium to do work. The law simply states that the total energy before = total energy after. Total energy = KE + PE in ALL classical formalisations. There are only the two choices, within thouse two there are many different options such as internal energy (temperature), gravitational potential energy, electrical potential energy etc... You are using options as a euphimism and you know it! All you need is the position, velocity and mass. In fact the equation of motion and the mass will do. Good point. The gravitational potential does change with height, even the force due to gravity changes with height, but even if you hold that constant you still have a scalar field for the potential energy. True, but in 1100' the change would be minimal. Convert -> to chagne from one energy to another. Thats part of it, theres also they fact that once converted the original form is lost. Chemical energy is expended when converted. You burn a log, converting it to heat, the log loses its original form and converts to ash. All forms of energy expend some type of fuel when converted to another form of energy. Energy is a property of things, you've taken that energy from the water and given it to something else, converted it. The technology to do that is indeed a development. If you can't tell me the form you mean when you say "that energy", you know like, solar energy or chemical energy, then what fuel is being expended in the conversion? The water simply has linear kinetic energy of the form E = 0.5 mv2 The water doesn't just simply have KE!!! KE cannot be created, remember, it had to come from somewhere! No, the origin of the KE does not influence it, it has been convereted from GPE to KE. It sounds like your trying to converting gravity to me. I ask again, how can you convert a constant? The gravity expends nothing maintaining its original form and PE in the field of the falling water. Can you at least tell me the fuel used in the conversion? Because the energy changes... Still waiting to hear the form your referring to... I'm not sure what you mean by define the form of energy that has the KE... The sentence makes no physical sense. I am not surprised. You have danced around the answer so many times I am running out of ways to ask a very simple question. I bet you would have no trouble defining the form of energy and the fuel expended, in a nuclear plant, coal plant, steam plant etc. Why can you not do the same for a hydroelectric plant? Link to comment Share on other sites More sharing options...
Klaynos Posted May 31, 2009 Share Posted May 31, 2009 In the real world, KE requires a medium to do work. No it doesn't, something is required to have the property of KE though... If you want to call that a medium fine, but in that case it'd be the water. You are using options as a euphimism and you know it! It's difficult to explain this trying to use words that lay people would understand. True, but in 1100' the change would be minimal. It's enough. Let's work it out! For a 1KG mass. Ending at the earths surface (6350 x 103m) 1100' ~ 367m Mass of the earth: 5.9742 × 1024kg Force due to gravity: [math]F = - \frac {GMm}{r^2}[/math] At the surface: 9.886747250 1100' above: 9.88604535 So a small difference, now the energy, we'll assume no change in the force, and therefore take g to be 9.886 as we calculated above.: [math]\Delta U=mgh[/math] U=3628J That's quite alot... Thats part of it, theres also they fact that once converted the original form is lost. Chemical energy is expended when converted. You burn a log, converting it to heat, the log loses its original form and converts to ash. All forms of energy expend some type of fuel when converted to another form of energy. They don't all expend a fuel. A pool ball hits a broken cushion and stops dead, it has lost all it's KE but has burnt no fuel. It's KE was converted into sound and heat in the cushion. If you can't tell me the form you mean when you say "that energy", you know like, solar energy or chemical energy, then what fuel is being expended in the conversion? You are requiring something that is not required by the universe. The water doesn't just simply have KE!!! Well actually it does. KE is a property of matter. So the water does just have KE. KE cannot be created, remember, it had to come from somewhere! Yes, it came from the GPE, it's postion in the potential well has changed so it's KE has to have changed as the total energy is the same. It sounds like your trying to converting gravity to me. Gravitational potential energy is being converted, not gravity. I ask again, how can you convert a constant? The gravity expends nothing maintaining its original form and PE in the field of the falling water. You are changing the waters position in a potential (gravity), therefore changing it's KE. Can you at least tell me the fuel used in the conversion? There is no fuel/ Still waiting to hear the form your referring to... I am not surprised. You have danced around the answer so many times I am running out of ways to ask a very simple question. I bet you would have no trouble defining the form of energy and the fuel expended, in a nuclear plant, coal plant, steam plant etc. Why can you not do the same for a hydroelectric plant? Because you refuse to accept that water can have KE. We would have exactly the same problem with any of the other plants as they use temperature (internal KE) to create a pressure in water (giving water KE) to turn a turbine, converting that KE to some other KE and then into electrical energy. Link to comment Share on other sites More sharing options...
navigator Posted May 31, 2009 Author Share Posted May 31, 2009 No it doesn't, something is required to have the property of KE though... If you want to call that a medium fine, but in that case it'd be the water. You contradicted yourself, not sure what you mean here. It's difficult to explain this trying to use words that lay people would understand. Touche' It's enough. Let's work it out! For a 1KG mass. Ending at the earths surface (6350 x 103m) 1100' ~ 367m Mass of the earth: 5.9742 × 1024kg Force due to gravity: [math]F = - \frac {GMm}{r^2}[/math] At the surface: 9.886747250 1100' above: 9.88604535 So a small difference, now the energy, we'll assume no change in the force, and therefore take g to be 9.886 as we calculated above.: [math]\Delta U=mgh[/math] U=3628J That's quite alot... Impressive, I am curious how that converts to amps? They don't all expend a fuel. A pool ball hits a broken cushion and stops dead, it has lost all it's KE but has burnt no fuel. It's KE was converted into sound and heat in the cushion. Your arm transferred force into the cue stick which transferred that force into the cue ball. Your arm expended fuel in the process:rolleyes: You are requiring something that is not required by the universe. Well actually it does. KE is a property of matter. So the water does just have KE. Yes, it came from the GPE, it's postion in the potential well has changed so it's KE has to have changed as the total energy is the same. Gravitational potential energy is being converted, not gravity. So the GPE doesn't have to become GKE in order to do work. If thats the case GPE should be re-classified as free energy, that is what your describing. Your really stretching now. You are changing the waters position in a potential (gravity), therefore changing it's KE. Back to reality...but this is not converting anything, but the path the water travels. There is no fuel/ Free energy? Please elaborate. Because you refuse to accept that water can have KE. We would have exactly the same problem with any of the other plants as they use temperature (internal KE) to create a pressure in water (giving water KE) to turn a turbine, converting that KE to some other KE and then into electrical energy. I never said the water doesn't have KE, what I did say is its not converted. I will ask you again, how can you validate your theory if you can't even identify the form of KE and its fuel you are reffering to? Like I said before, you would have no problem doing this with any other power plant, whats so unique about this one? Link to comment Share on other sites More sharing options...
Klaynos Posted May 31, 2009 Share Posted May 31, 2009 You contradicted yourself, not sure what you mean here. It's not a medium in a traditional sense. Touche' You are playing a game? Impressive, I am curious how that converts to amps? That would depend on the generator. Your arm transferred force into the cue stick which transferred that force into the cue ball. Your arm expended fuel in the process The ball rolled down a small slope. The situation is completely independent of how the ball started rolling we're talking about the deceleration not the acceleration. So the GPE doesn't have to become GKE in order to do work. If thats the case GPE should be re-classified as free energy, that is what your describing. It's not free it is closely related to your position in the potential well. Your really stretching now. Not stretching at all, trying to explain to you the physical reality. Back to reality...but this is not converting anything, but the path the water travels. You are changing something you are changing it's position in a potential. Free energy? Please elaborate. It's not free, it's related to the position in a potential, in this case a gravitational potential. I never said the water doesn't have KE, what I did say is its not converted. You were wrong. I will ask you again, how can you validate your theory if you can't even identify the form of KE and its fuel you are reffering to? There is no form other than linear KE, you can measure the velocity and mass at different points and from that work out all the energies... Like I said before, you would have no problem doing this with any other power plant, whats so unique about this one? Please see my response to the same thing you said before we would have the same problem for the turbine process in those power plants. Link to comment Share on other sites More sharing options...
D H Posted June 1, 2009 Share Posted June 1, 2009 First, I need to get something off my chest. Are you trying to be a crackpot, navigator? If that is your goal, you are well on the way. You have all the trademarks: Intentional obtuseness, tortured logic, ignoring evidence, intellectual dishonesty. OK. Now that I got that off my chest I can address your concerns. Think of a boat with an electrically powered propeller. You can find these on everything from tiny little toy boats all the way up to supertankers. Electricity powers an electric motor which turns the propeller. The blades on the rotating propeller create a stream of rearward-moving water. Newton's third law: The boat moves forward. An electric boat demonstrates conversion of energy from one form to another multiple times over. The electricity might come from a battery, a deisel-powered generator, a nuclear power plant, or a solar cell. Energy of some sort is converted to electrical potential energy. The electric motor converts this electrical energy to rotational kinetic energy. The rotating propeller, thanks to its blades, transforms this rotational kinetic energy to translational kinetic energy, some of that transfered to the water and some transfered to the boat itself. Now imagine the boat is firmly anchored. Turning the propeller will still transfer energy to the water. It will in fact transfer more energy to the water than was transfered when the boat was free to move. There won't be much energy wasted in making the boat move. Last step: Reverse the process. Instead of the propeller accelerating the water, imagine a moving stream of water hitting the stationary propeller. The propeller will turn, which in turn will turn the motor's rotor. Conceptually there is very little difference between a generator and a motor. Apply electricity to a motor/generator and you get rotary motion out. Apply rotary motion to a motor/generator and you get electricity out. Link to comment Share on other sites More sharing options...
navigator Posted June 1, 2009 Author Share Posted June 1, 2009 First, I need to get something off my chest. Are you trying to be a crackpot, navigator? If that is your goal, you are well on the way. You have all the trademarks: Intentional obtuseness, tortured logic, ignoring evidence, intellectual dishonesty. Resorting to personal attacks only shows you cannot answer the question either. OK. Now that I got that off my chest I can address your concerns. Think of a boat with an electrically powered propeller. You can find these on everything from tiny little toy boats all the way up to supertankers. Electricity powers an electric motor which turns the propeller. The blades on the rotating propeller create a stream of rearward-moving water. Newton's third law: The boat moves forward. An electric boat demonstrates conversion of energy from one form to another multiple times over. The electricity might come from a battery, a deisel-powered generator, a nuclear power plant, or a solar cell. Energy of some sort is converted to electrical potential energy. The electric motor converts this electrical energy to rotational kinetic energy. The rotating propeller, thanks to its blades, transforms this rotational kinetic energy to translational kinetic energy, some of that transfered to the water and some transfered to the boat itself. All youv'e done is used euphimisms for mechanical energy, in an effort to avoid actually naming it. Then it won't seem so odd that you cannot tell me the form of energy converted in a hydroelectric system. Now imagine the boat is firmly anchored. Turning the propeller will still transfer energy to the water. It will in fact transfer more energy to the water than was transfered when the boat was free to move. There won't be much energy wasted in making the boat move. Last step: Reverse the process. Instead of the propeller accelerating the water, imagine a moving stream of water hitting the stationary propeller. The propeller will turn, which in turn will turn the motor's rotor. Conceptually there is very little difference between a generator and a motor. Apply electricity to a motor/generator and you get rotary motion out. Apply rotary motion to a motor/generator and you get electricity out. Mechanical energy turned the prop. Another form of energy, electrical, nuclear, etc. was converted into the mechanical energy at the cost of expending some of the PE in the electricity, uranium, etc. I really don't see what reversing the process does??? I am perplexed that I have been labeled a crackpot, because nobody can tell me what form of energy is being converted, a very elementary question. A nuclear plant uses uranium/fuel to increase the pressure in the system and convert it to another more usable form of energy depending on the demand. The uranium is expended changing it from PE to KE. I don't think I need to continue describing the processes in coal plants, steam plants, etc. you get the point. The point I am not getting, is why a layman can explain the processes in other plants, but you "experts" cannot tell me what form of energy is converted in a Hydroelectric plant. Link to comment Share on other sites More sharing options...
D H Posted June 1, 2009 Share Posted June 1, 2009 The point I am not getting, is why a layman can explain the processes in other plants, but you "experts" cannot tell me what form of energy is converted in a Hydroelectric plant. For crying out loud! You have been told you many times over what form of energy is converted into electricity in a hydroelectric plant. It is gravitational potential energy. Link to comment Share on other sites More sharing options...
navigator Posted June 1, 2009 Author Share Posted June 1, 2009 (edited) Potential energy is work done by a conservative force. Total energy does not change — this is shown by Noether's theorem; conservation of energy is a consequence of physics not changing over time. All the rest is a discussion of semantics of the merits of using "convert," and there's already a consensus. Deal with it. This is a physics board, and the thread is not discussing physics. I don't really see any reason to leave it open. The intent was to discuss the Law of energy Conservation and how it relates to the processes in a hydroeletric system. If I started the thread in the wrong forum, I apologize. This could be ended very easily, but nobody is able to tell me what is being converted other than saying KE, which only describes the state the energy is in, not its form. Its no wonder technology around energy has progressed so little in the last 100 years. Merged post follows: Consecutive posts mergedFor crying out loud! You have been told you many times over what form of energy is converted into electricity in a hydroelectric plant. It is gravitational potential energy. In order for it to be converted, some must have been expended. Are you saying that the gpe in the field the water falls is decreased? Earlier in the thread Swansont agreed that GPE was not being converted. I have been told that, but after being reminded that you cannot convert a constant everybody backs away from that position??? Edited June 1, 2009 by navigator Consecutive posts merged. Link to comment Share on other sites More sharing options...
D H Posted June 1, 2009 Share Posted June 1, 2009 This could be ended very easily, but nobody is able to tell me what is being converted other than saying KE, which only describes the state the energy is in, not its form. Kinetic energy is a thing in and of itself. It is not potential energy. This is a big part of your problem. The gravitational potential energy of a jet flying at supersonic speed at an elevation of 1000 feet over the ocean is exactly equal to the jet's gravitational potential energy when it lands on an airfield with an elevation of 1000 feet above sea level. Gravitational potential energy is a function of height and mass only. Velocity doesn't enter into the picture. The same goes for the chemical potential energy of the fuel in the jet. Whether the jet is traveling at Mach 2 or sitting still on the ground doesn't matter. The chemical potential energy depends only on the quantity of fuel in the jet's tanks. In order for it to be converted, some must have been expended. Are you saying that the gpe in the field the water falls is decreased? Yes. The change in gravitational potential energy in some packet of falling water is [math]mgh[/math], where h is the distance the packet has fallen. Look at it this way. Suppose you carry a ball to the top of a cliff of height h and release it. The ball starts with a velocity of zero (zero kinetic energy) and falls to the bottom of the cliff. Ignoring friction with the air, what is the velocity of the ball right before it hits the ground at the bottom of the cliff? The answer is easily obtained if you look at the problem from the perspective of conservation of energy. The ball loses mgh gravitational potential energy in falling. Therefore, the ball's gain in kinetic energy must be equal to mgh to conserve energy. The ball's velocity at the end is v directed downwards, so its kinetic energy is ½mv2. Put the two together, [math]mgh=\frac 1 2 mv^2[/math], and the ball's velocity right before it hits is [math]\sqrt{2gh}[/math]. Alternatively, you could use Newton's second law and after considerably more work come up with exactly the same answer. Looking at this problem from the perspective of conservation of energy and the answer pops out. Link to comment Share on other sites More sharing options...
swansont Posted June 1, 2009 Share Posted June 1, 2009 Earlier in the thread Swansont agreed that GPE was not being converted. I have been told that, but after being reminded that you cannot convert a constant everybody backs away from that position??? Gravity is not the same thing as gravitational potential energy, which is the work gravity has done. The acceleration from gravity is g, the force of gravity is mg, and GPE is mgh (when g is a constant). NOBODY has said that g has changed, or mg has changed. The intent was to discuss the Law of energy Conservation and how it relates to the processes in a hydroeletric system. If I started the thread in the wrong forum, I apologize. This could be ended very easily, but nobody is able to tell me what is being converted other than saying KE, which only describes the state the energy is in, not its form. If that was the purpose, it was the right forum, and has long been answered. All the rest is squabbling about semantics, which is distilled in the last sentence here — you seem to think that "state" and "form" have different meanings in this context, and they do not. There is no physics being discussed by you. Thread closed Link to comment Share on other sites More sharing options...
Recommended Posts