Is Newton right?

[xfwayne]

Newton's law states that energy cannot be created or destroyed. If that's the case then, how can electricity be created?

 

[Mrs. Enigma]

Electricity isn't created, it is just converted from one form to another. How does that sound?????

 

[freak_of_today]

I dont have my physics text book in front of me, but Mrs Enigme is right. Electricity (and other forms of energy) are not just 'created'. Just as it takes flour and water and eggs etc. to make a cake it takes many ingrediants to make electricity. Depending on what type (whether it be hydro, nuclear, fission, gas etc) depends on wat happens.



For example, hydro electricity..... energy comes in the form of water flowing through a river/canal/ tube/whatever. It is then tranfered into mechanical energy to moce the turbine which tranfers the mechanical energy into electricity.

 

[Tachocline]

Newton's laws make no statement about energy conservation, period.

 

[OneLastBreath]

Not true Tachocline. The law of conservation of energy can be (and was) derived directly from Newton's laws of motion.
I) An object at rest tends to stay at rest, and object in motion tends to stay in motion.
If an object has no kinetic energy, it won't spontaneously gain energy. Therefore energy can't come from nowhere. If an object does have kinetic energy then it will tend to hold onto that energy. Therefore energy can't spontaneously dissappear into thin air either.
II) The acceleration an object undergoes (which gives it kinetic energy) is proportional to the ratio of the force applied to the object's mass. (F = ma)
III) For action there is an equal and opposite reaction.
Using these two laws together with the first one we can surmise that (from III), since energy can't spontaneously disappear, when an object with kinetic energy is slowed down or stopped (action) there must be a reaction, or a resulting force. Therefore, the energy is transformed into a force on another object or system. (From II), since energy can't spontaneously appear and since F = ma, kinetic energy is the result of a force which itself the result of transformed energy.
Energy is universal, so what applies to one form of energy, kinetic energy, applies to them all. An object gaining kinetic energy from falling is transforming it's potential energy from it's height, which is from the kinetic energy it gained from you lifting it up there, which is from the kinetic energy in your muscles, which is from the chemical potential energy in your muscles, which is from the chemical potential energy in the food you ate, which can be tied back to the nuclear energy of the sun, all the way back to when God created the Universe, the only time when mass-energy (according to relativity, they're 2 sides of the same coin) WAS created. Hence we can see that some form of energy contained in an object or system is the direct result of the transforming of energy, maybe in another form, from another system, both part of a larger system. As demonstrated, this is predicted from Newton's three laws of motion and gives a self-contained resolution to the apparent paradox in the first law of where energy comes from and goes. xfwayne, I hope my little hierarchy there also helped to answer your question.

 

[ThePhoenix]

What? Talk about putting the cart in front of the horse. The principles of Newton's laws of conservation descend directly from the laws of thermodynamics. And your statement of them is wrong too, as "Kinetic energy" tends to just go away. Kick a ball and watch it loose all of it's kinetic energy pretty quickly.

 

[Deamiter]

Good point. You really can't derive energy conservation from Newton's laws as they deal almost entirely with inertia and momentum. Of course to a lay-person they may be used to suggest energy conservation, but proof takes a little more work.

OneLastBreath's later statements about energy, though confusing, are correct. At first, as Phoenix pointed out, he seems to equate kinetic energy with TOTAL energy which is quite wrong. NO object will spontaniously gain energy, that fact isn't limited to those without kinetic energy. His use of "therefore" makes little sense in that light because he seem to be claiming that a specific case has proven a general fact.

I guess the point is to be more careful how we present cause/effect relationships when discussing physics. People get confused enough as it is without making errors in an attempt to make it more understandable.

 

[kurabrhm]

Newton's law states that energy cannot be created or destroyed. If that's the case then, how can electricity be created?

Surely the basic principle is that energy is a potential.
So if its a potential then there's always the possibility to create it, or put it another away there's always a way to fulfill that potential. Just like any potential (for instance, human potential - eg: a person's potential to be a scientist or a doctor - usefull stuff just as electricity!!!), there's also the way to destroy it by not doing enough to fulfiill that potential in the first place. So there's a moral relativism to this whole argument as well as my human analogy illustrates!!

 

[Deamiter]

Um... kurabrhm, did you read any of our responses before you posted? The only thing you've managed to illustrate is that you don't understand energy!

Energy is most definately NOT a potential. It's like it's other form, matter, in that it CANNOT just be created. It is also quite IMPOSSIBLE to destroy energy! Try taking the energy output of an atomic bomb and 'destroying' it so that the bomb has no effect on the city... If it WERE possible, you'd CERTAINLY get a nobel prize for showing it!

Furthermore, the conclusions you draw from your flawed arguments don't logically follow from the arguments you presented! There would be a logical argument for moral relitavism if energy were merely a potential? Huh?

Then again, maybe you were joking... Either way, don't mislead innocent civilians about science as they're often confused enough as it is!

 

[kurabrhm]

Um... kurabrhm, did you read any of our responses before you posted? The only thing you've managed to illustrate is that you don't understand energy!

Energy is most definately NOT a potential. It's like it's other form, matter, in that it CANNOT just be created. It is also quite IMPOSSIBLE to destroy energy! Try taking the energy output of an atomic bomb and 'destroying' it so that the bomb has no effect on the city... If it WERE possible, you'd CERTAINLY get a nobel prize for showing it!

Furthermore, the conclusions you draw from your flawed arguments don't logically follow from the arguments you presented! There would be a logical argument for moral relitavism if energy were merely a potential? Huh?

Then again, maybe you were joking... Either way, don't mislead innocent civilians about science as they're often confused enough as it is!

At its most elementary, energy may not be a potential because its existence is undeniable and its practically everywhere, however, if you take the example of a human being who has energy but does not use it through for example walking or running, then that energy becomes a potential.

 

[Deamiter]

haha.... funny. I assume you noticed that the point of the thread was NEWTON's laws which have really very little to do with a human's potential... In a physical science forum, I'd expect that when one mentions Newton's laws, the meaning would be apparent.

Anyway, talking about energy in the human body, it's still not a potential. Until the carbohydrates or fat is converted into energy (which is used immediately either to fuel muscles or to store fat which can be later turned into energy. Of course it's a bit more complicated than that, but the point is that there is never any "stored energy" or potential in any sort of physical sense. Of course there are things that can be CONVERTED into energy but there's no form of energy either biological or physical that can be "destroyed" or created.

 

[OneLastBreath]

What? Talk about putting the cart in front of the horse. The principles of Newton's laws of conservation descend directly from the laws of thermodynamics. And your statement of them is wrong too, as "Kinetic energy" tends to just go away. Kick a ball and watch it loose all of it's kinetic energy pretty quickly.

I realize thermodynamics is the key to the conservation laws, however I just showing, using kinetic energy as an example (I apologize for the use of the word therefore, I didn't mean to equate the two). The previous post had said that Newton's laws had nothing to do with conservation of energy, I was just showing that his laws of motion and the conservation of energy are connected, in that energy can't simply disappear or appear, and so they do have something to do with each other.

 

[Amalthea]

This thread is terrible. Newton's laws have not only nothing to do with conservation laws neither does thermodynamics. I recommend all of you to right away enroll in a graduate physics curriculum.

 

[FromTheAshes]

This thread is terrible. Newton's laws have not only nothing to do with conservation laws neither does thermodynamics. I recommend all of you to right away enroll in a graduate physics curriculum.

Um, ok. I kinda thought that a law stated as:

* 1st Law: Conservation of energy. This is a fundamental principle of mechanics, and more generally of physics. In thermodynamics, it is used to give a precise definition of heat. It is stated as follows:

The work exchanged in an adiabatic process depends only on the initial and the final state and not on the details of the process.

or

The heat flowing into a system equals the increase in internal energy of the system minus the work done by the system.

Might just have something to do with Conservation of energy. http://en.wikipedia.org/wiki/Thermodynamics

But enlighten us anyway. What grand law makes the first law of thermodynamics have nothing to do with conservation?

 

[Amalthea]

Thermodynamics is technically an observation from experiment. It is not fundamental in and of itself. Newton's laws of motion have nothing to do with energy conservation directly.

Energy conservation (from which you can derive thermodynamics as measured by experiment) is a consequence of symmetries in spacetime. Just like angular momentum conservation is a consequence of the rotational symmetry of space. Symmetries in nature imply an associated conservation law via a theorem of theroretical physics called Noethers theorem.

 

[Deamiter]

Just out of idle curiosity, isn't energy conservation derived from observation by experiment as well? It's not as if we have a divinely inspired book outlining the symmetries in spacetime from which we derived energy conservation!

Perhaps on a very technical level, thermodynamics differs from energy conservation (and certainly it would be bad form to assume energy conservation from thermodynamics) but you CAN derive formulas for energy conservation starting with thermodynamics if you assume thermodynamics works (which is shown by experiment).

Anyway, moving away from arguing the technical merits of a particular derivation, perhaps we should be willing to explain things on a slightly lower level than graduate physics... Not only are there many people here who are not in science at ALL (like the origional poster with his question about electricity) those that ARE probably won't be taking graduate level physics. As much as I love to be corrected on little technicalities (so I don't FAIL graduate physics in the future) I'm afraid many others do not.

 

[FromTheAshes]

Thermodynamics is technically an observation from experiment. It is not fundamental in and of itself. Newton's laws of motion have nothing to do with energy conservation directly.

Observation from experiment is exactly what scientific theories are based on. I'm sorry if you like symmetries in spacetime, but the fact of the matter is that the law that states that is the first law of thermodynamics. The why of the first law is interesting, cool, and theoretical. I'm sorry, but the first law of thermodynamics works.

As a simple thought experiment to see which is more critical to the conservation of energy, imagine that some form of evidence disproved Noether's theorum. Now imagine some form of evidence disproved the first law of thermodynamics. Which would cause the conservation of energy to be tossed out the window and why?

Energy conservation (from which you can derive thermodynamics as measured by experiment) is a consequence of symmetries in spacetime. Just like angular momentum conservation is a consequence of the rotational symmetry of space. Symmetries in nature imply an associated conservation law via a theorem of theroretical physics called Noethers theorem.

Yes, and the equations probably give computers headaches. But it's a group of variables. An ounce of observation is worth more then a ton of theory.

 

[Amalthea]

A more fundamental property of space is it's symmetries than an experimental result in a lab. The first law of thermodynamics is a statement of energy conservation from experiment. But if you break the symmetries of spacetime then it would not apply and your experiment would give a different result. This would be the case say near a singularity where you lose the symmetry in question.

You are thinking like an engineer and not a physicist. Noether's theorem is a mathematical statement that is proven.

Conservation of energy probably may not apply in certain situations and even if some other conservation law can be formulated in the extreme situations where standard thermodynamics breaks down then it wont take the same form.

An ounce of observation is only worth something in the regime you perform the experiment.

I advise you, if you don't believe me, to check out the textbooks for a graduate curriculum in theoretical physics.

 

[FromTheAshes]

A more fundamental property of space is it's symmetries than an experimental result in a lab. The first law of thermodynamics is a statement of energy conservation from experiment. But if you break the symmetries of spacetime then it would not apply and your experiment would give a different result. This would be the case say near a singularity where you lose the symmetry in question.

You are thinking like an engineer and not a physicist. Noether's theorem is a mathematical statement that is proven.

A huge surprise... I am an engineer. And all of those beautiful equations have to be based on experiment for them to have real-world application. Therefore if an experiment discovered that a previous experiment that proved part of the prepositions used by Noether in his theorum were incorrect a different explaination would have to be found. Pure math is nice, but in the end it's exactly as good as the engineer who set up the equipment for the experiment.

Conservation of energy probably may not apply in certain situations and even if some other conservation law can be formulated in the extreme situations where standard thermodynamics breaks down then it wont take the same form.

Like?

An ounce of observation is only worth something in the regime you perform the experiment.

But if a thousand theories cannot explain that observation then each and every one of them is wrong.

I advise you, if you don't believe me, to check out the textbooks for a graduate curriculum in theoretical physics.

Oh I'm sure they explain conservation with Noether's theorum. But it's based in the laws of thermodynamics, the experimental results that allowed him to formulate his theorum.

 

[Amalthea]

A huge surprise... I am an engineer.

I could tell, and no offence but engineers seem to often not understand physics.

And all of those beautiful equations have to be based on experiment for them to have real-world application. Therefore if an experiment discovered that a previous experiment that proved part of the prepositions used by Noether in his theorum were incorrect a different explaination would have to be found. Pure math is nice, but in the end it's exactly as good as the engineer who set up the equipment for the experiment.

Again an engineer speaking. Physics is more than real world experiment. By the way Emmy Noether was a woman!

Noether's theorem is purely mathematical use of the variational principle of calculus. If the 'action' is unchanged under some group of tranformations on the coordinates and the scalar field then there exist conserved quantities. This is physics at the fundamental level. The conservation of energy is the time translational symmetry of spacetime, period.

Like?

Think where a flat spacetime breaks down. On the global cosmological scale there are problems formulating energy conservation and near the Big Bang singularity. The 2nd Law has a similar problem as you cannot define the arrow of time that synopsises the 2nd Law of thermodynamics.

Oh I'm sure they explain conservation with Noether's theorum. But it's based in the laws of thermodynamics, the experimental results that allowed him to formulate his theorum.

Absolutely incorrect. The laws of thermodynamics originally were based on experiment. See James Joules work for instance.

You can approach them theoretically via energy conservation but this technically requires a Minkowskian spacetime. Take that away and you don't necessarily have this. You are putting the cart before the horse and starting off from thermodynamics. You strictly cannot do this. Practically as in an engineering sense you can get away with it but that doesn't make it right. Remember, engineers engineer things, physicists do science.