Is potential energy real or fictious?

[aditya23456]

Is body at higher altitude having more potential energy than a body on Earth real.? Does this mean a person at 400th floor has more capacity to do work than a person on ground floor(concerning precisely)
Or is concept of potential energy just introduced to satisfy law of conservation of energy..If potential energy really exists,can a person with higher potential be more heavier than other ( considering in a high gravity field) by E=mc2

 

[A.T.]

Or is concept of potential energy just introduced to satisfy law of conservation of energy.

Not just potential energy. The whole point of the concept of energy in general is to have a conserved quantity.

 

[Drakkith]

Potential energy is real in the sense that an object falling from 10 feet has the ability to perform more work on a system than an object falling from 5 feet. If we actual perform such an experiment we will find that the higher the object is dropped from the more kinetic energy it has, hence we have defined such a concept as "potential energy".

And yes, if I were to measure the mass of both you and the Earth, once when you are stationary at 1 million miles above the surface, and one where you are stationary on the Earths surface, the former example would indeed be more massive.

 

[Dead Boss]

Does this mean a person at 400th floor has more capacity to do work than a person on ground floor(concerning precisely)

Of course but it would probably have unfortunate consequences for him if he tried to utilize this extra energy.
Imagine that there is a vertical spring on the ground. The person on the ground floor can jump on the spring and say he will compress the spring a little. Now the person on the 400th floor can jump on the spring and intuitively you know that he will compress it a lot more since there is more force on the impact. Compressing the spring more means doing more work (the distance is greater) so the 400th floor person can do more work just because he is on the 400th floor.

Whether potential energy is real or not depends on your definition of real.

 

[sophiecentaur]

Is body at higher altitude having more potential energy than a body on Earth real.? Does this mean a person at 400th floor has more capacity to do work than a person on ground floor(concerning precisely)
Or is concept of potential energy just introduced to satisfy law of conservation of energy..If potential energy really exists,can a person with higher potential be more heavier than other ( considering in a high gravity field) by E=mc2

So the office space at the top of high buildings should cost more (increased staff productivity)
But that may not be what you mean.

 

[DragonPetter]

Keep in mind potential energy is always used with a reference "ground" level, and when you grab two random objects with different potential energies, you need to be aware of what they are being referenced to. If you cannot reference them to the same ground level, it is almost meaningless to compare their potential energies directly.

This is why your question is confusing or misleading, because it seems to want to imply a mixing up of references (you combine the potential energy of height/gravity with human body chemical potential, which are not both referenced to the same energy). If you want to talk about capability to do work of a person at different heights, then the gravity potential energy between the two systems cancels out and you only would consider their chemical energy which should be the same, and so you would conclude that their height has no impact on their ability to do work, unless you mean for them to fall to ground level.

 

[mikelepore]

Does this mean a person at 400th floor has more capacity to do work than a person on ground floor

No, but if they jump out the window, gravity has more of an opportunity to do work on the person on the 400th floor, as seen by the final speeds that they acquire just before they hit the ground.

(Check on the sign: gravitational force is downward, displacement is downward, force is in the same direction as the displacement, therefore work has a positive sign, therefore the object gains kinetic energy.)

 

[aditya23456]

Keep in mind potential energy is always used with a reference "ground" level, and when you grab two random objects with different potential energies, you need to be aware of what they are being referenced to. If you cannot reference them to the same ground level, it is almost meaningless to compare their potential energies directly.

This is why your question is confusing or misleading, because it seems to want to imply a mixing up of references (you combine the potential energy of height/gravity with human body chemical potential, which are not both referenced to the same energy). If you want to talk about capability to do work of a person at different heights, then the gravity potential energy between the two systems cancels out and you only would consider their chemical energy which should be the same, and so you would conclude that their height has no impact on their ability to do work, unless you mean for them to fall to ground level.

Wait a person on higher altitude from Earth's surface is having more potential energy,then how can gravitational potential energy be same and cancel out.?

 

[DragonPetter]

Wait a person on higher altitude from Earth's surface is having more potential energy,then how can gravitational potential energy be same and cancel out.?

Consider someone on the top floor of a 400 floor building, and someone on the ground floor.

If they both have the same human body and are going to push 100kg desks, then they both have the same potential energy to do work on these desks, regardless of their gravitational potential energy with respect to each other. The way you asked your original question about their capacity to do work while being at different heights, and your implication that you wonder if potential energy is not real lead me to think that your contention is that the increase in gravitational potential energy gives the person a higher absolute potential energy with respect to the objects that they might do work on, as in your example objects on the same floor as the person. If that were true, which it isn't, then it would make sense for you to question if potential energy is not real since this is not what we experience.

Just because one person has a higher gravitational potential energy does not mean that that potential energy is relevant when you compare two people's ability to do work. When you talk about their capacity to do work, such as pushing a desk, you are using 2 different potential energy references for the two cases, and so it does not make sense to say a person on a higher floor has more potential energy when any work they do on that floor will be at the same gravitational potential energy, and thus cancel out when compared to someone on a different floor in the building.

 

[aditya23456]

my definition of reality is - anything which can physical effect and be the source of a cause which can be observed..

So since all of them say its immaterial abt being in 400th or ground floor..so can potential energy concept be fictious which is introduced just to make conservation of energy possible.

 

[dipole]

And yes, if I were to measure the mass of both you and the Earth, once when you are stationary at 1 million miles above the surface, and one where you are stationary on the Earths surface, the former example would indeed be more massive.

I don't buy this. If you separate two objects you must do work, but the energy goes into the gravitational field, not the mass of the objects. Now you can argue that the field has "mass", which it does in some sense I suppose, but if I push on an object at the surface of the Earth or at 1 million miles away, it should respond in the same way, it hasn't gained any more inertial mass.

 

[DrewD]

So since all of them say its immaterial abt being in 400th or ground floor..so can potential energy concept be fictious which is introduced just to make conservation of energy possible.

Nobody said it was immaterial. It just won't effect your ability to push a desk across the floor. But the person on the 400th floor can do significantly more work by pushing the desk out the window. Reread what dragonpetter wrote.
Potential energy is equally as real as forces, kinetic energy, your age, time, and anything else that we use numbers to represent.

 

[Drakkith]

I don't buy this. If you separate two objects you must do work, but the energy goes into the gravitational field, not the mass of the objects. Now you can argue that the field has "mass", which it does in some sense I suppose, but if I push on an object at the surface of the Earth or at 1 million miles away, it should respond in the same way, it hasn't gained any more inertial mass.

I believe you would have to measure the mass of the Earth and the object together as a system.

 

[Drakkith]

my definition of reality is - anything which can physical effect and be the source of a cause which can be observed..

So since all of them say its immaterial abt being in 400th or ground floor..so can potential energy concept be fictious which is introduced just to make conservation of energy possible.

Arguing what is "real" and what isn't is fairly pointless. EVERYTHING is a concept in some way. Does an electron "really" exist? We can interact with something that causes our instruments to record a certain mass, charge, spin, etc. But who is to say that is "really" an electron, or that it "really" exists and isn't just an effect by some unknown "thing" making us believe it is an electron.

The fact is that potential energy is a real concept that has a specific definition as used by science. This is no different than energy. Energy is also an abstract quantity. It isn't something "real" by your definition. You cannot feel it, see it, etc. You only feel the effects of a force applied by something. When we do the math we find out that it is convenient to define a concept describing the potential ability of a system to have an effect on another system based on their current states. Energy is our concept. It represents the amount of change that one system can cause on another.

 

[sophiecentaur]

"Real" often means no more than "what I feel comfortable about". And it's all in your head, when you get down to it.

 

[A.T.]

.so can potential energy concept be fictious which is introduced just to make conservation of energy possible.

All forms of energy are introduced just to make conservation of energy possible. The is no other purpose to the whole concept of energy, than to have a conserved quantity.

 

[sophiecentaur]

The is no other purpose to the whole concept of energy, than to have a conserved quantity.

Try telling that to your electricity company!
"Dear Sir, I don't see why I should be paying your bills - you are only maintaining a conserved quantity."
Like I said, it's all to do with familiarity.

 

[A.T.]

Try telling that to your electricity company!
"Dear Sir, I don't see why I should be paying your bills - you are only maintaining a conserved quantity."

Would you rather pay money for a quantity that is not conserved, and can be created out of nothing? That would be stupid. In theory the value of your money should also be conserved, but this is unfortunately not a law of physics.

 

[sophiecentaur]

Would you rather pay money for a quantity that is not conserved, and can be created out of nothing? That would be stupid. In theory the value of your money should also be conserved, but since this is unfortunately not a law of physics.

Haha. But the laws of money are not conservative. It changes value to suit the economic climate. I would just hope the failure of conservation would be in my favour. But then, I'm not a banker.

 

[Nano-Passion]

All forms of energy are introduced just to make conservation of energy possible. The is no other purpose to the whole concept of energy, than to have a conserved quantity.

I'm not convinced, I'm in the philosophy that things should ultimately make sense or else we don't understand it. If we just invented a few concepts to make the math work than it implies that we have missing holes in our understanding. I think a good role model is the equation for rest energy "mc^2." It seems that it takes us a bit closer to the fundamental.

"Real" often means no more than "what I feel comfortable about". And it's all in your head, when you get down to it.

Kinetic energy seems more real than potential energy. Potential energy just says particle A has so and so potential.

Kinetic energy tells me that I can deal this much damage with a bullet with mass m and velocity v.

Arguing what is "real" and what isn't is fairly pointless. EVERYTHING is a concept in some way. Does an electron "really" exist? We can interact with something that causes our instruments to record a certain mass, charge, spin, etc. But who is to say that is "really" an electron, or that it "really" exists and isn't just an effect by some unknown "thing" making us believe it is an electron.

The fact is that potential energy is a real concept that has a specific definition as used by science. This is no different than energy. Energy is also an abstract quantity. It isn't something "real" by your definition. You cannot feel it, see it, etc. You only feel the effects of a force applied by something. When we do the math we find out that it is convenient to define a concept describing the potential ability of a system to have an effect on another system based on their current states. Energy is our concept. It represents the amount of change that one system can cause on another.

You seem to take the "real" argument a bit too far. Electrons are more real than potential energy. One is tangible and we use it in our daily lives even if it isn't what we "really" think it is, while the latter sounds like a bookkeeping device.

 

[aditya23456]

Nano-Passion
I guess ur right..Can physics hold without concept of potential energy.?I guess not..so we need to believe it irrespective of it being real or fictious

 

[Nano-Passion]

Nano-Passion
I guess ur right..Can physics hold without concept of potential energy.?I guess not..so we need to believe it irrespective of it being real or fictious

It would have helped if it was explicitly stated. I've spent many hours grappling with the subject of potential energy. I'm the type of person that has to know a "why" for everything, so the superficiality of introductory physics texts drove me crazy.

 

[Drakkith]

I'm not convinced, I'm in the philosophy that things should ultimately make sense or else we don't understand it. If we just invented a few concepts to make the math work than it implies that we have missing holes in our understanding. I think a good role model is the equation for rest energy "mc^2." It seems that it takes us a bit closer to the fundamental.

Just because it doesn't make sense to you doesn't mean we don't understand it. Energy and potential energy are "made up" in the same way that mass or charge is made up. All are simply properties of something that we have defined a certain way.

Kinetic energy seems more real than potential energy. Potential energy just says particle A has so and so potential.

Kinetic energy just says particle A can do such and such amount of work.

Kinetic energy tells me that I can deal this much damage with a bullet with mass m and velocity v.

And potential energy let's you state how much energy something can acquire in the first place.

You seem to take the "real" argument a bit too far. Electrons are more real than potential energy. One is tangible and we use it in our daily lives even if it isn't what we "really" think it is, while the latter sounds like a bookkeeping device.

Neither is more real than the other unless you personally define one to be. And yes, you do use potential energy in your everyday life even if you don't realize it. Something as simple as knowing that riding a bicycle downhill will result in a very high speed unless you ride the brakes is a direct result of you knowing what potential energy is. Not in a scientific way, but in a functional way. The concept of potential energy is very real. It is simply different than an electron.

 

[russ_watters]

I'm not convinced, I'm in the philosophy that things should ultimately make sense or else we don't understand it.

Well of course - you don't understand it, so it doesn't make sense to you. Just don't say "we" because there are plenty of us who do understand it.

If we just invented a few concepts to make the math work than it implies that we have missing holes in our understanding.

Welcome to physics. I'm sorry it isn't satisfying to you, but that's all [!] physics is.

Kinetic energy seems more real than potential energy. Potential energy just says particle A has so and so potential.

Kinetic energy tells me that I can deal this much damage with a bullet with mass m and velocity v.

Whatever problem you have with potential energy surely also exists for kinetic. I'm guessing your problem with potential energy is its frame dependence -- the same also exists for kinetic energy. The damage a bullet can do is not a singular quantity: it depends on what the bullet is being measured against. So as I said in your other thread: potential energy is exactly as "real" as kinetic.

You seem to take the "real" argument a bit too far. Electrons are more real than potential energy. One is tangible and we use it in our daily lives even if it isn't what we "really" think it is, while the latter sounds like a bookkeeping device.

This is why this is a just plain bad question. The word "real" is poorly defined and really isn't useful here regardless of what it means. If you mean that to be real, it has to be an object, then information of any kind is not real, whether it is kinetic energy, potential energy or War and Peace. But this definition has no real value - calling it "real" or "not real" doesn't change its usefulness in physics, so it is just a bad question to ask.

It would have helped if it was explicitly stated. I've spent many hours grappling with the subject of potential energy. I'm the type of person that has to know a "why" for everything, so the superficiality of introductory physics texts drove me crazy.

That's why you've been having so much trouble learning physics for so long on PF. You're asking meaningless questions, looking for existential meanings behind concepts in physics that just don't exist and ignoring the actual meanings of the concepts. This "real" or "not real" thing you are into on energy is not useful. Getting an answer that satisfies you will not in any way help you understand what energy is and in fact is acting as a substitute for learning what it actually is.

 

[Nano-Passion]

Just because it doesn't make sense to you doesn't mean we don't understand it. Energy and potential energy are "made up" in the same way that mass or charge is made up. All are simply properties of something that we have defined a certain way.

I don't agree with the philosophical premise that mass and charge are just as made up as a more abstract concept as potential energy. It is a bit relative, but mass and charge has direct affects to our daily lives in comparison to potential energy.

Kinetic energy just says particle A can do such and such amount of work.

And potential energy let's you state how much energy something can acquire in the first place.

You can derive how much energy something can have through other means?

Neither is more real than the other unless you personally define one to be. And yes, you do use potential energy in your everyday life even if you don't realize it. Something as simple as knowing that riding a bicycle downhill will result in a very high speed unless you ride the brakes is a direct result of you knowing what potential energy is. Not in a scientific way, but in a functional way. The concept of potential energy is very real. It is simply different than an electron.

That is easily explained by saying that there is a constant acceleration down that is usually counteracted by the normal force, and once you are on a slope, there is less normal force to counteract the gravitational acceleration.

 

[Nano-Passion]

Well of course - you don't understand it, so it doesn't make sense to you. Just don't say "we" because there are plenty of us who do understand it. Welcome to physics. I'm sorry it isn't satisfying to you, but that's all [!] physics is.
Whatever problem you have with kinetic energy

I understand it potential energy. It isn't that complicated. What is complicated is how it is talked about so often like its something of substance.

Whatever problem you have with potential energy surely also exists for kinetic. I'm guessing your problem with potential energy is its frame dependence -- the same also exists for kinetic energy. The damage a bullet can do is not a singular quantity: it depends on what the bullet is being measured against. So as I said in your other thread: potential energy is exactly as "real" as kinetic. This is why this is a just plain bad question. The definition of "real" is poorly defined. If you mean that to be real, it has to be an object, then information of any kind is not real, whether it is kinetic energy, potential energy or War and Peace. But this definition has no real value - calling it "real" or "not real" doesn't change its usefulness in physics, so it is just a bad question to ask.

I was speaking in the casual sense not the literal sense.

It is useful for calculation but it is just as equally useless by not being a fundamental aspect of nature. There might be an alternative formalism to account for the conservation of energy.

 

[russ_watters]

That is easily explained by saying that there is a constant acceleration down that is usually counteracted by the normal force, and once you are on a slope, there is less normal force to counteract the gravitational acceleration.

Yes, that's fine. Physicists decided that that needed a name so they wouldn't have to type it all out every time they wanted to refer to it! That's how concepts in physics get names. They also noticed that that could calculated/quantified, so they use it in equations.

I understand it potential energy. It isn't that complicated. What is complicated is how it is talked about so often like its something of substance.

I don't know what you mean or how this relates to your previous claim that "we" don't understand it. Again, this all seems pretty meaningless.

It is useful for calculation but it is just as equally useless by not being a fundamental aspect of nature.

I'm sorry, but that is just psuedophilosophical babbling. There is no such idea in science as "a fundamental aspect of nature", but even if there was, both kinetic and potential energy would rank the same on whatever scale you would use to measure the concepts.

Please be clearer: what exactly is it about potential energy that you don't like and how does kinetic energy differ?

There might be an alternative formalism to account for the conservation of energy.

If it looks like a duck and quacks like a duck, you can call it a chicken if you want, but it is still a duck.

 

[Nano-Passion]

Yes, that's fine. Physicists decided that that needed a name so they wouldn't have to type it all out every time they wanted to refer to it! That's how concepts in physics get names. They also noticed that that could calculated/quantified, so they use it in equations.

That is perfectly fine, but then it isn't real in the sense that some of the other concepts in physics are, its bookkeeping.

I don't know what you mean or how this relates to your previous claim that "we" don't understand it.

I said the previous statement on the assumption that potential energy was supposed to be a type of energy that affects the system's behavior, but now I see that not everyone follows that paradigm.

Again, this all seems pretty meaningless. I'm sorry, but that is just psuedophilosophical babbling. There is no such idea in science as "a fundamental aspect of nature", but even if there was, both kinetic and potential energy would rank the same on whatever scale you would use to measure the concepts.

Some things are more fundamental than others. This has been the case ever since we have looked for equations that describe the very small and ever since the search for unification.

I'm not sure why it is noted that kinetic and potential energy are on the same scale.

The kinetic energy "of an object is the energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity.

Potential energy "is the energy of a body or a system due to the position of the body or the arrangement of the particles of the system"

Kinetic energy is more tangible in the sense that we can use it to describe a lot of everyday phenomena such as the energy imparted on a ball by a bat swing. Potential energy seems like an accountant's tool to make sure all the toys in the box and out count up to X.

Please be clearer: what exactly is it about potential energy that you don't like and how does kinetic energy differ? If it looks like a duck and quacks like a duck, you can call it a chicken if you want, but it is still a duck.

See comment above.

 

[sophiecentaur]

I don't agree with the philosophical premise that mass and charge are just as made up as a more abstract concept as potential energy. It is a bit relative, but mass and charge has direct affects to our daily lives in comparison to potential energy.

and many other quotes.

You are being very selective in your appreciation of Science. You base the above statement on a very narrow appreciation of the three example quantities. How can you be any more 'aware' of the presence of a mass or a charge other than by how they are reacting with you or something else? You drop a mass on your foot but its effect (how painful it gets) depends entirely upon its gravitational potential energy where you let it go. On Earth, it might break your toe but on the Moon it may just bounce off your shoe.

You are trying to impose a very personal view on all of this. Moreover, the further this thread goes, the more entrenched you seem to be getting. If you go away and think about this, rather than bouncing back with more and more arguments, trying to justify your view, then you may start to realize the advantage of thinking the way 'the rest of us' are thinking. When you do come to that conclusion, don't think of it as having been proved wrong. Just feel and enjoy the enlightenment. None of this is 'real'; it's just ways of thinking about things which allow us to make good predictions.

 

[A.T.]

I'm in the philosophy that things should ultimately make sense or else we don't understand it. If we just invented a few concepts to make the math work than it implies that we have missing holes in our understanding.

"Making sense" and "understanding" are rather vague subjective terms and quite irrelevant to the goal of physics: making quantitative predictions. The concepts allow us to do this. Whether the concepts are intuitive to some person is very individual.

I don't agree with the philosophical premise that mass and charge are just as made up as a more abstract concept as potential energy.

The original question was whether potential energy is somehow "more made up to ensure CoE" than other forms of energy. It's not. All the formulas to calculate various forms of energy are designed to ensure of CoE. Without CoE the concept of energy would be useless.

I would agree that subjectively, to most humans, the concept of energy as such is more abstract than say length, which humans can perceive more directly. Energy is more general and can be computed for apparently unrelated phenomena, which makes it hard to grasp it intuitively.

 

[Michio Cuckoo]

My god you people keep on arguing on what is real or not, even making me confused when I wasn't before.

Look, energy is force * distance. When you are repelled by an object, it exerts a force on you. Your kinetic energy is converted to potential energy, which determines how close you get to the object before stopping.

For god's sake.

 

[sophiecentaur]

"Making sense" and "understanding" are rather vague subjective terms and quite irrelevant to the goal of physics: making quantitative predictions. The concepts allow us to do this. Whether the concepts are intuitive to some person is very individual.

Absolutely. √-1 makes very little sense to most people at first but it soon becomes meat and drink to those of us who have got over the initial "doesn't seem right" reaction. Some of the most abstract concepts get to feel at least as concrete as length and force when we use them regularly.

It's not unlike the taste of beer - which nearly all kids will gag at but most of us blokes find most acceptable.

 

[sophiecentaur]

For god's sake.

Deepest sympathy.
We do a lot of angels on pinheads here.

The problem is that your approach may be a bit too simplistic if you want to progress to higher levels of this game. For instance, your definition of Energy is usually regarded as the definition of Work.

 

[DrewD]

That is perfectly fine, but then it isn't real in the sense that some of the other concepts in physics are, its bookkeeping.

All of physics is book keeping. What is a force except a number that is used to describe a change in momentum. It may seem more real because you can see something move. If you define that to be real, then you are correct.

Every physical system can be described in a formalism that uses only energy and not force. Very little modern physics considers forces at all. Instead, the formalism of Hamiltonian Mechanics is often used (I have to admit that a friend recently published a paper that heavily relied on forces for her analysis) which is based on kinetic and potential energy. Since the Newtonian and Hamiltonian Mechanics can both equally well describe the world without reference to the other, it seems to me that their basic components must be equally real.

Also, look up Aharonov-Bohm effect. It is certainly not the same thing, but since the relationship of force to force field is similar to energy to potential field it might help convince you. In short, this effect shows that the electromagnetic potential field can have measurable effects on particles where there is no electric field. Weird, yes. Also very real.

What level of physics have you studied? I expect that when you get to an upper level Mechanics course and QM, you will be better convinced that potential energy and forces are on the same level. As to using the word "real", leave it to the philosophy majors. They need something to do.

 

[harrylin]

[..] I said the previous statement on the assumption that potential energy was supposed to be a type of energy that affects the system's behavior, but now I see that not everyone follows that paradigm.[..]

You may say so - I did not see all comments here, but that one looks fine to me - in that sense you could argue that potential energy (or at least, a difference or a ratio between potential energies) is "real". :tongue2:

For example a clock at higher gravitational potential (cet.par.) is found to be ticking faster, but a clock with equally more kinetic energy is found to be ticking at the same rate* - which also goes to illustrate, as mentioned earlier, that kinetic and potential energy could be said to be equally "real".

*for references you can look up information about satellite clocks or clocks on the geoid in relation to GR.