Sisyphus Posted May 29, 2009 Posted May 29, 2009 I think your hang-up here is that you're only looking at the potential energy. The total energy is always conserved. When water flows downhill, some of the potential energy is converted into other forms of energy, which in total is exactly equal to the amount of potential energy lost. By sticking a turbine in the flow, we create a situation where some of that other energy is useful to us.
navigator Posted May 29, 2009 Author Posted May 29, 2009 I think your hang-up here is that you're only looking at the potential energy. The total energy is always conserved. When water flows downhill, some of the potential energy is converted into other forms of energy, which in total is exactly equal to the amount of potential energy lost. By sticking a turbine in the flow, we create a situation where some of that other energy is useful to us. Maybe science taught in schools these days is hung up twisting the definitions of words in order to fit them into their comfort zone of how things work. Would you consider potential energy a type or form of energy? I am also curious as to your "off the cuff" definition of energy?
swansont Posted May 29, 2009 Posted May 29, 2009 You guys are throwing words around paying little attention to their definition. Lets take two dams, one with the turbine developing mechanical energy, the other with no mechaical objects in the path of the water, just the open penstock directly into the lower resevoir which is identical to the system with the turbines lower resevoir. If I captured some of the potential energy from the falling the water hitting the turbines,then potentials, once all the water has collected into the two lower resevoirs, would be different. PE = mgh Your potential energy, which is going to be the maximum amount of work you could extract from the water, is zero at the bottom, where h=0. It does not matter if there is a turbine in the way or not. If there is a turbine there, you do work on it, and it means the water has less kinetic energy when it reaches the bottom. [math]KE_o + PE_o + W = KE_f + PE_f[/math]
Sisyphus Posted May 29, 2009 Posted May 29, 2009 How about an analogy? Consider a campfire. It has a set amount of wood for fuel, and will burn for as long as the chemical potential energy in the wood lasts. That potential energy will be converted into light and heat. Now suppose an identical fire, in which we place a steam turbine over it. The water is boiled, the steam turns a wheel, which powers a dynamo, which produces electricity. In both cases, the same amount of potential energy is "used up," by which I mean is converted into different forms of energy. In only one case, however, is some of that energy used to do useful work for us. With the non-turbine fire, the energy that would eventually be used to produce electricity simply goes unused by us, and mostly just heats the air above the flame. It is the same with the turbine in the dam. When the floodgate is just open and the turbine is bypassed, gravitational potential energy is still converted into other forms of energy, it just goes unused. In that case, mostly as kinetic energy, in the form of faster moving water.
navigator Posted May 29, 2009 Author Posted May 29, 2009 PE = mgh Your potential energy, which is going to be the maximum amount of work you could extract from the water, is zero at the bottom, where h=0. It does not matter if there is a turbine in the way or not. If there is a turbine there, you do work on it, and it means the water has less kinetic energy when it reaches the bottom. [math]KE_o + PE_o + W = KE_f + PE_f[/math] I interpet, you do work on it, in this context as spinning the turbine. If spinning the turbine was a result of converting the potential energy, then by definition, the result would be less potential energy in the lower resevoir than the system without the turbine. Sounds like your telling me that the system with no turbine expends more potential energy just free falling, rather than slamming into a turbine blade with many thousands of lbs. of pressure behind it. And it also knows exactly how much mechanical energy the turbine system is generating so it can expend the exact amount in order for the potential energy in the lower resevoirs to end up equal. That is what would have to happen if you use the word convert.
Sisyphus Posted May 29, 2009 Posted May 29, 2009 Alright, how about a simplification. Dam A has no turbine. Dam B has a turbine. Dam A: A unit of water at the top of dam A has 10 units of gravitational potential energy. At the bottom, that same unit of water has 0 units of potential energy and 10 units of kinetic energy. Dam B: A unit of water at the top of dam B has 10 units of gravitational potential energy. At the bottom, that same unit of water has 0 units of potential energy and 5 units of kinetic energy. Along the way, 5 units of kinetic energy were used to turn the turbine, and generate 5 units of electricity. It's not as simple as that, of course. There's friction and other inefficiencies (which is why the river doesn't just get faster and faster indefinitely). But that's the basic idea.
navigator Posted May 29, 2009 Author Posted May 29, 2009 How about an analogy? Consider a campfire. It has a set amount of wood for fuel, and will burn for as long as the chemical potential energy in the wood lasts. That potential energy will be converted into light and heat. Now suppose an identical fire, in which we place a steam turbine over it. The water is boiled, the steam turns a wheel, which powers a dynamo, which produces electricity. In both cases, the same amount of potential energy is "used up," by which I mean is converted into different forms of energy. In only one case, however, is some of that energy used to do useful work for us. With the non-turbine fire, the energy that would eventually be used to produce electricity simply goes unused by us, and mostly just heats the air above the flame. It is the same with the turbine in the dam. When the floodgate is just open and the turbine is bypassed, gravitational potential energy is still converted into other forms of energy, it just goes unused. In that case, mostly as kinetic energy, in the form of faster moving water. I disagree. While there are some similarities, the main difference I see is the wood, a finite amount, is the vehicle supplying the fuel for the fire. A hydroelectric dam uses water as a vehicle for the force of gravity, which is a constant or even infinate force of nature, as the fuel to spin the turbines. When your fire goes out all you have is ash. The water reaches the bottom of the two resevoirs, there is still the same amount of water. The wood was converted to ash. The water still has the same volume and chemical make-up. If anything is converted its the force of gravity, although it is a constant that cannot be converted. By definition, develop, is the term that comes the closest to defining what is happening. It is using the force of gravity on water to develop mechanical energy, its not using the water like the wood in your analogy.
Sisyphus Posted May 29, 2009 Posted May 29, 2009 The water is also finite, and it is very much analogous to the log. The difference is just between chemical potential energy and gravitational potential energy. The log releases energy by undergoing a chemical reaction that releases extra heat. The water releases energy by moving from a higher point to a lower point. There is the same amount of water afterwards, but there is no more "higher up" water. This might not be intuitive, because the "higher up" water is constantly replenished, by sunlight evaporating water from the oceans and lifting it up to cloud level.
navigator Posted May 29, 2009 Author Posted May 29, 2009 Alright, how about a simplification. Dam A has no turbine. Dam B has a turbine. Dam A: A unit of water at the top of dam A has 10 units of gravitational potential energy. At the bottom, that same unit of water has 0 units of potential energy and 10 units of kinetic energy. Dam B: A unit of water at the top of dam B has 10 units of gravitational potential energy. At the bottom, that same unit of water has 0 units of potential energy and 5 units of kinetic energy. Along the way, 5 units of kinetic energy were used to turn the turbine, and generate 5 units of electricity. It's not as simple as that, of course. There's friction and other inefficiencies (which is why the river doesn't just get faster and faster indefinitely). But that's the basic idea. Or at the bottom of dam A the water hits the surface at 100 mph and dam b the water hits the surface of 50mph? I would agree, but didn't man develop the distance of the head to the turbine increasing the velocity? Velocity is the only difference in the kinetic energy right above the surface of the lower resevoirs and velocity directly effects the output of the dam, the only thing converted is the path of the water. The volume is not converted into anything and remains the same. Merged post follows: Consecutive posts mergedThe water is also finite, and it is very much analogous to the log. The difference is just between chemical potential energy and gravitational potential energy. The log releases energy by undergoing a chemical reaction that releases extra heat. The water releases energy by moving from a higher point to a lower point. There is the same amount of water afterwards, but there is no more "higher up" water. This might not be intuitive, because the "higher up" water is constantly replenished, by sunlight evaporating water from the oceans and lifting it up to cloud level. The wood converts to ash, the water in the bottom resevoir remains the same, but is no more "higher up" water. Thats a big difference to me I guess. The wood is gone because it was converted. The water can go from potential to kinetic and back again without losing volume. There are systems in use that use a dam to generate elec. during the day and at night, when elec. is a fraction of the price, pump the water back into the upper resevoir.
Klaynos Posted May 30, 2009 Posted May 30, 2009 I would agree, but didn't man develop the distance of the head to the turbine increasing the velocity? Velocity is the only difference in the kinetic energy right above the surface of the lower resevoirs and velocity directly effects the output of the dam, the only thing converted is the path of the water. The volume is not converted into anything and remains the same. The velocity difference is important. The less velocity the less energy. So some of it must have been converted to other forms of energy. As in both dams the starting potential is the same. So after the same height changes the potential energy is converted into kintetic energy. If you drop 10m you gain the same amount of kinetic energy no matter how many times you do it. So what we do is we put a turbine in the way which converts the kinetic energy of the water into mechanical (and then electrical) energy. This slows the water path down, if you remove the turbine fins and leave everything else the same the velocities at the bottom would be the same for the two water paths....
swansont Posted May 30, 2009 Posted May 30, 2009 I interpet, you do work on it, in this context as spinning the turbine. If spinning the turbine was a result of converting the potential energy, then by definition, the result would be less potential energy in the lower resevoir than the system without the turbine. No, because of there is no turbine, the water has more kinetic energy. The potential energy is the same. The potential energy it started with gets converted into either kinetic energy of the turbine, or of the water (ignoring heat and sound for the moment) Sounds like your telling me that the system with no turbine expends more potential energy just free falling, rather than slamming into a turbine blade with many thousands of lbs. of pressure behind it. And it also knows exactly how much mechanical energy the turbine system is generating so it can expend the exact amount in order for the potential energy in the lower resevoirs to end up equal. That is what would have to happen if you use the word convert. No, you are anthropomorphizing the situation (known as that pathetic fallacy). The amount of energy the turbine generates is dictated by the energy of the water, not the the way around. —— Since energy is conserved, you can look at the problem at any point. Right before the water hits the turbine, it has a certain amount of kinetic energy (which was potential energy earlier). This does work on the turbine, and reduces the kinetic energy of the water.
navigator Posted May 30, 2009 Author Posted May 30, 2009 (edited) The velocity difference is important. The less velocity the less energy. So some of it must have been converted to other forms of energy. As in both dams the starting potential is the same. So after the same height changes the potential energy is converted into kintetic energy. Yes, the velocity is very important given f=mv2. The system with the turbine is using the velocity and mass of the water to turn the turbine and therefore has less kinetic energy as a result of less velocity, not less volume, right before it reaches the surface of the lower resevoir, than the system without the turbine. The energy converted shows up as a velocity difference and not the volume of water difference, but you cannot convert velocity, by definition, you can only increase or decrease it. If you drop 10m you gain the same amount of kinetic energy no matter how many times you do it. So what we do is we put a turbine in the way which converts the kinetic energy of the water into mechanical (and then electrical) energy. This slows the water path down, if you remove the turbine fins and leave everything else the same the velocities at the bottom would be the same for the two water paths.... I say again...nothing is converted except the path of the water. If there is a conversion of kinetic energy to mechanical energy, the volume of water would have to be different when it reached the lower resevoir. The definition of convert clearly states when you convert something you change it from one form to another and the original form is lost. This can be seen in the burning log analogy earlier in the thread. The burning wood converts the potential energy into heat. Because the original form of wood turns to ash, it is correct to use convert. But if I throw that same log and harness the kinetic energy from the motion of the log and store it in a battery, when the log becomes still again, I have increased the total potential energy. What changed? the velocity of the log, not its form, volume or chemical make-up. It still holds the same to potential if it were to to be put in motion again. You cannot convert velocity, but we can harness or develop it using any form of matter as a medium. Merged post follows: Consecutive posts mergedNo, because of there is no turbine, the water has more kinetic energy. The potential energy is the same. The potential energy it started with gets converted into either kinetic energy of the turbine, or of the water (ignoring heat and sound for the moment) The water has less kinetic energy just above the surface of lower resevoir of the system with the turbine due to the change in velocity, not volume of water. Velocity cannot be converted, only increased and decreased, and since the volume of water remains the same there is no conversion. No, you are anthropomorphizing the situation (known as that pathetic fallacy). The amount of energy the turbine generates is dictated by the energy of the water, not the the way around. The only two varibles that determine the amount of kinetic energy in the falling water is mass and velocity, fact. The volume of water is not decreased, therefore it was not converted into anything, fact. The velocity of the water is decreased, due to impacting the turbine blades causing them to spin. If the velocity is being converted then you must redefine velocity, because, by definition velocity can only be increased or decreased. Since energy is conserved, you can look at the problem at any point. Right before the water hits the turbine, it has a certain amount of kinetic energy (which was potential energy earlier). This does work on the turbine, and reduces the kinetic energy of the water. The reduction is due to less velocity, not the volume/mass. Please, explain to me how you convert velocity? Edited May 30, 2009 by navigator Consecutive posts merged.
D H Posted May 30, 2009 Posted May 30, 2009 What is your intent in this thread, navigator? Are you about to introduce some crackpot notion, or are you just confused? If it's the latter, re-read post #28. Also, google for conservation of energy.
Klaynos Posted May 30, 2009 Posted May 30, 2009 Consider a rail with a cart on it. The cart is moving at 10m/s. It weighs 2KG. It has KE of 100J. There is no friction or wind resistance. Now a wind turnbine that is on the cart is turned on, this generates some electricity for charging a battery. This turbine will add some resistance. After 5 mins the cart is moving at only 5m/s. It now has 25J of KE. The other 75J have been converted into electrical energy. There has been no mass change. E=0.5mv2 You can change eitehr the mass OR the velocity to change the energy.
navigator Posted May 30, 2009 Author Posted May 30, 2009 What is your intent in this thread, navigator? Are you about to introduce some crackpot notion, or are you just confused? If it's the latter, re-read post #28. Also, google for conservation of energy. My intent in this thread is too see if my theory can be invalidated by facts and not twisting of definitions. All forms of energy have a fuel or source that is expended when the energy goes from potential to kinetic, except mechanical energy. The only way we can produce mechanical energy is by converting a different form of energy into mechanical energy. This is done by applying force to matter. My theory is any type of matter in motion is the fuel or source for mechanical energy and it can be freely developed. It does not create something from nothing. It does not convert something to something else. It develops the kinetic energy that is present when you put matter in motion. Thomas Young coined the term energy and defined it as "work stored within". To me that means all matter has energy stored within, therefore potential mechanical energy is in all matter. If you studied classical mechanics in any depth you understand some of the phenomenans that occur when you put different types of matter in motion. Are you familiar with the brenoulli principles dealing with air/gas and water/fluid? Can you give me a reason I shouldn't expect third type of matter to also show unique charateristics? Crack-pot notion? Maybe I am wrong about the way this thread has gone, but it seems to me most are just using different terms in place of convert, I guess because it sounds better. The fact is they are just as incorrect as using the term convert for the process that happens with a dam, a windmill and an airplane wing etc.The fact that I am not encumbered by the old science taught in school today and understand that theories are proven wrong everyday actually gives me a leg up. What I know about classical mechanics and fluid flow and the rest I learned from google search. 2000 years prior to Galileo, it was accepted as fact that a 10lb rock falls faster than a 1 lb rock. It wasn't till Galileo actually dropped the two rocks and realised the truth.
Sisyphus Posted May 30, 2009 Posted May 30, 2009 Where is there "twisting definitions?" Anyway, if it helps you, you can think of the "fuel" being expended as the hydrogen in the sun. It undergoes fusion and is converted into helium, giving off a lot of extra energy. That energy is radiated outwards in all directions as electromagnetic waves, some of which hit the Earth. These warm the oceans and stir the atmosphere, causing a continuous supply of water to evaporate and be carried into the upper atmosphere, thus gaining a great deal of gravitational potential energy, "converting" it into gravitational potential energy, if you want. Not that there needs to be fuel in way you're thinking. The total amount of energy always remains constant, and it can often be "converted" and forth between different kinds. If I'm going back and forth on a 100% efficient swing (which can't exist in nature, but that's a different story), I'm converting gravitational potential energy (at the top, when I have zero velocity) into kinetic energy (at the bottom, where I'm moving fastest) and back again over and over. Oh, and comparing yourself to Galileo is the UNIVERSAL crackpot red flag...
navigator Posted May 30, 2009 Author Posted May 30, 2009 Where is there "twisting definitions?" Lets get back to that... Anyway, if it helps you, you can think of the "fuel" being expended as the hydrogen in the sun. It undergoes fusion and is converted into helium, giving off a lot of extra energy. That energy is radiated outwards in all directions as electromagnetic waves, some of which hit the Earth. These warm the oceans and stir the atmosphere, causing a continuous supply of water to evaporate and be carried into the upper atmosphere, At this point the energy from the sun is useless, if it wasn't for gravity the process would stop. thus gaining a great deal of gravitational potential energy, "converting" it into gravitational potential energy, if you want. I think you want it to sound correct, but this is the very twisting of definitions I spoke of. The fact is, gravity is a constant force of nature that cannot be converted. It is an invisible force that requires a medium to "show" itself. This also explains the reason you "quoted" converting. Your subconscience mind remembers english class and knows the only way your statement is close to factual is if converting is used as a euphimism for develop. Not that there needs to be fuel in way you're thinking. The total amount of energy always remains constant, and it can often be "converted" and forth between different kinds. If I'm going back and forth on a 100% efficient swing (which can't exist in nature, but that's a different story), I'm converting gravitational potential energy (at the top, when I have zero velocity) into kinetic energy (at the bottom, where I'm moving fastest) and back again over and over. A fuelless energy? What way are you thinking? When you convert something you lose its original form. The water, which is the medium gravity uses to turn the turbines does not lose its original form nor does the gravity... Again all you have done is redefine gravity by adding energy to it. What is the fuel/source of so-called gravitational energy? Oh, and comparing yourself to Galileo is the UNIVERSAL crackpot red flag...
Klaynos Posted May 30, 2009 Posted May 30, 2009 In classical mechanics there are only two energies that are ever considered: Kinetic energy and potential energy. There are lots of different forms of these, mechanical energy for example is just a form of kinetic energy... Merged post follows: Consecutive posts mergedForce and potential energy are intamately linked by: [math] - \frac {dU} {dx} = F[/math] This is well known and gravitational potential energy is part of netwons formation of gravity.
navigator Posted May 30, 2009 Author Posted May 30, 2009 (edited) In classical mechanics there are only two energies that are ever considered: Kinetic energy and potential energy. There are lots of different forms of these, mechanical energy for example is just a form of kinetic energy... Merged post follows: Consecutive posts mergedForce and potential energy are intamately linked by: [math] - \frac {dU} {dx} = F[/math] This is well known and gravitational potential energy is part of netwons formation of gravity. I googled "netwons formation of gravity" got zero exact matches but I did find this at one of my favorite sites... Gravitational potential energy is energy an object possesses because of its position in a gravitational field. The most common use of gravitational potential energy is for an object near the surface of the Earth where the gravitational acceleration can be assumed to be constant at about 9.8 m/s2. http://hyperphysics.phy-astr.gsu.edu/HBASE/gpot.html For the sake of debate lets discuss "gravitational potential energy". It is not the term so much as the context you are trying to use it. You cannot convert gravity, it doesn't change and it always remains constant, regardless of how much work it does. If gravitational kinetic energy is the source for the force used to spin the turbine then the correct term, again, is develop because the gravity is still in its original form and maintained its potential. In a dam, using f=mv2, mass is the weight of the water and velocity defines its speed, which is result of the force of gravity. The difference takes place in the velocity and path of the water. The dam with no turbine accelerates until it reaches terminal velocity or it reaches the botttom resevoir. The system with the dam the water velocity increases and then decreases when it hits the turbines, changing its path, and then accelerates again until it reaches terminal velocity or it reaches the bottom resevoir. The conversion is in the velocity of the water, but velocity is a unit of measure, not energy. If there is gravitational potential energy then shouldn't there also be velocitational potential energy, since that is whats being converted? Edited May 30, 2009 by navigator
swansont Posted May 30, 2009 Posted May 30, 2009 (edited) The water has less kinetic energy just above the surface of lower resevoir of the system with the turbine due to the change in velocity, not volume of water. Velocity cannot be converted, only increased and decreased, and since the volume of water remains the same there is no conversion. The only two varibles that determine the amount of kinetic energy in the falling water is mass and velocity, fact. The volume of water is not decreased, therefore it was not converted into anything, fact. The velocity of the water is decreased, due to impacting the turbine blades causing them to spin. If the velocity is being converted then you must redefine velocity, because, by definition velocity can only be increased or decreased. The reduction is due to less velocity, not the volume/mass. Please, explain to me how you convert velocity? I never said anything about converting velocity. I don't think anyone has proposed anything about volume (or mass) changing, either. You are the only one bring that up, and it's a non-sequitur, a strawman. A big part of this seems to be a semantic argument about the word "convert." We classify the forms of energy — potential and kinetic, and the changes in them due to work being done. Any change is sometimes referred to as converting the energy to a different type. That's simply the way it is. Merged post follows: Consecutive posts mergedFor the sake of debate lets discuss "gravitational potential energy". It is not the term so much as the context you are trying to use it. You cannot convert gravity, it doesn't change and it always remains constant, regardless of how much work it does. If gravitational kinetic energy is the source for the force used to spin the turbine then the correct term, again, is develop because the gravity is still in its original form and maintained its potential. Nobody is claiming to convert gravity. Stop it already. What is being discussed is energy, and converting it from one form to another. In a dam, using f=mv2, mass is the weight of the water and velocity defines its speed, which is result of the force of gravity. The difference takes place in the velocity and path of the water. The dam with no turbine accelerates until it reaches terminal velocity or it reaches the botttom resevoir. The system with the dam the water velocity increases and then decreases when it hits the turbines, changing its path, and then accelerates again until it reaches terminal velocity or it reaches the bottom resevoir. The conversion is in the velocity of the water, but velocity is a unit of measure, not energy. If there is gravitational potential energy then shouldn't there also be velocitational potential energy, since that is whats being converted? Energy due to being in motion is called kinetic energy. I have to ask: are you being intentionally obtuse, or are you trying to tackle this problem without the benefit of having taken physics 101? It wasn't clear from your earlier post if you've learned all of this from Google Edited May 30, 2009 by swansont Consecutive posts merged.
Klaynos Posted May 30, 2009 Posted May 30, 2009 Newton* it was a typo... http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation You are changing the position of some mass in a gravitational potential, this results in a change in the potentail energy of the system, this change results in the mass having a larger kinetic energy.
navigator Posted May 31, 2009 Author Posted May 31, 2009 I never said anything about converting velocity. I don't think anyone has proposed anything about volume (or mass) changing, either. You are the only one bring that up, and it's a non-sequitur, a strawman. I brought it up because the context the term convert is being used is factually wrong, unless your refferring to the velocity. Volume of water not changing is unique, can you not see that? Any other form of energy is expended when convertered to another form. Here the velocity of the water developed more energy and maintains its original form, albeit less with less potential energy than the original potential, but it is equal to the system where the falling water did no work, just fall. A big part of this seems to be a semantic argument about the word "convert." We classify the forms of energy — potential and kinetic, and the changes in them due to work being done. Any change is sometimes referred to as converting the energy to a different type. That's simply the way it is. Didn't you mean to say, we classify the types of energy, potential and kinetic, into different forms and the changes in them due to work being done? Didn't you mean to say, any change is always, not sometimes, reffered to as converting the energy to a different type? Nobody is claiming to convert gravity. Stop it already. What is being discussed is energy, and converting it from one form to another. So we agree, gravity is not being converted. Can you please end this and tell me which form of energy is being converted? Energy due to being in motion is called kinetic energy. I have to ask: are you being intentionally obtuse, or are you trying to tackle this problem without the benefit of having taken physics 101? It wasn't clear from your earlier post if you've learned all of this from Google I find it ironic that you feel like I am being obtuse when I am just trying to understand all the terms that are continually missused. If you don't understand what I mean go back to the middle of this post and reread. Merged post follows: Consecutive posts mergedNewton* it was a typo... http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation You are changing the position of some mass in a gravitational potential, this results in a change in the potentail energy of the system, this change results in the mass having a larger kinetic energy. I would call that using technological developments to develop free mechanical energy.
swansont Posted May 31, 2009 Posted May 31, 2009 I brought it up because the context the term convert is being used is factually wrong, unless your refferring to the velocity. Volume of water not changing is unique, can you not see that? Any other form of energy is expended when convertered to another form. Here the velocity of the water developed more energy and maintains its original form, albeit less with less potential energy than the original potential, but it is equal to the system where the falling water did no work, just fall. No, it's not wrong to use "convert." to change from one form or function to another and to exchange for an equivalent are both relevant. Nobody has claimed that the volume of water has changed. The physical attributes of the water are not affected here — it is the classification of the type of energy that the water has. We have potential energy, due to position, and we have kinetic energy, due to motion. The water can also do mechanical work, which will change the energy it has. A big part of this seems to be a semantic argument about the word "convert." We classify the forms of energy — potential and kinetic, and the changes in them due to work being done. Any change is sometimes referred to as converting the energy to a different type. That's simply the way it is. Didn't you mean to say, we classify the types of energy, potential and kinetic, into different forms and the changes in them due to work being done? Didn't you mean to say, any change is always, not sometimes, reffered to as converting the energy to a different type? Type and form are interchangeable in this discussion. I didn't say "always," because some people might not use it. One could use e.g. transform, change or turn. So we agree, gravity is not being converted. Can you please end this and tell me which form of energy is being converted? Potential energy is being converted into kinetic energy, and/or mechanical work. I have to ask: are you being intentionally obtuse, or are you trying to tackle this problem without the benefit of having taken physics 101? It wasn't clear from your earlier post if you've learned all of this from Google I find it ironic that you feel like I am being obtuse when I am just trying to understand all the terms that are continually missused. If you don't understand what I mean go back to the middle of this post and reread. I asked a question, since there were (to my mind) two options at this point. And I have to note that you didn't answer it. The terms aren't being misused. They are defined in a certain way and are used consistently within those definitions. You appear to want to apply different definitions, and are apparently surprised that it causes confusion.
navigator Posted May 31, 2009 Author Posted May 31, 2009 No, it's not wrong to use "convert." to change from one form or function to another and to exchange for an equivalent are both relevant. Nobody has claimed that the volume of water has changed. The physical attributes of the water are not affected here — it is the classification of the type of energy that the water has. We have potential energy, due to position, and we have kinetic energy, due to motion. The water can also do mechanical work, which will change the energy it has. The amount of work the water does in these two systems is different, because one increases the amout of potential energy over the other, but they will always have equal amount of potential at the bottom. The water could generate 1 megawatt or a 1000 megawatts and the final potential will in the lower resevoirs will always be equal. The change in the energy is due to its height, not the mechanical work it did. Type and form are interchangeable in this discussion. I didn't say "always," because some people might not use it. One could use e.g. transform, change or turn. How so? Kinetic and potential energies are types of energy. Nuclear, chemical, electrical, mechanical, magnetic and radient are all forms of energy that contain both types of energy, the type of energy defines what state a form of energy is in. The only way you can say they are interchangable is if your trying to intentionally confuse someone. Potential energy is being converted into kinetic energy, and/or mechanical work. What form of energy are you saying is being converted? I asked a question, since there were (to my mind) two options at this point. And I have to note that you didn't answer it. I did answer and gave you a reason for my confusion. My physics 101 teacher tried to use a whole chalkboard of mathematical equations to prove 1+1=3, he was also unable to tell me which form of energy is being converted in a hydroelectric dam. I sincerely do not understand how convert can be correctly used in this context. When you convert something you change its original form into something else and in doing so you lose the original form. The terms aren't being misused. They are defined in a certain way and are used consistently within those definitions. You appear to want to apply different definitions, and are apparently surprised that it causes confusion. If you can just tell me which form of energy is being converted it should clear up any confusion.
Klaynos Posted May 31, 2009 Posted May 31, 2009 The amount of work the water does in these two systems is different, because one increases the amout of potential energy over the other, but they will always have equal amount of potential at the bottom. The water could generate 1 megawatt or a 1000 megawatts and the final potential will in the lower resevoirs will always be equal. But their kinetic energy wont be the same in the bottom reservoir... That is the important bit. Merged post follows: Consecutive posts mergedThe 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.
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