Potential Energy

[DrRocket]

I hope this is the correct place to post this:

How is gravitational potential energy stored?, because all the other energy I know about is kinetic (like an electron that moves faster has more energy than other that is slower) or in form of mass (E=mc^2). But I don't see any of them doing something there.

 

Off of topic, my native language isn't English so tell me if you don't understand what I'm trying to say.

 

The usual explanation is that, as for electromagnetic energy, it is stored in the field.

 

There is a problem when trying to carry this over to general relativity. Conservation of energy in general relativity is both subtle and problematic.

[swansont]

I hope this is the correct place to post this:

How is gravitational potential energy stored?, because all the other energy I know about is kinetic (like an electron that moves faster has more energy than other that is slower) or in form of mass (E=mc^2). But I don't see any of them doing something there.

 

Off of topic, my native language isn't English so tell me if you don't understand what I'm trying to say.

It's "stored" because there is a force that can do work, and is position dependent, as with gravity or the electrostatic force. The force can do work and give the object some kinetic energy.

[mooeypoo]

Why is it so hard for people who like math to acknowledge how much of science involves non-mathematic ideas and concepts?

 

Because it isn't; the math is an underlying layer of the "concepts and ideas". The fact you don't understand them doesn't mean they're not true. You were asked to pick up a physics book so that you can see it for yourself and learn a bit of why the explanations are what they are. You can't refuse to cooperate and then claim the other people are ignorant, lemur.

 

 

Now, please get back on topic. There was an actual question asked, and the discussion was moved to other questions instead.

 

 

 

 

~mooey

[Dekan]

I hope this is the correct place to post this:

How is gravitational potential energy stored?, because all the other energy I know about is kinetic (like an electron that moves faster has more energy than other that is slower) or in form of mass (E=mc^2). But I don't see any of them doing something there.

 

Off of topic, my native language isn't English so tell me if you don't understand what I'm trying to say.

 

 

Thanks zoteman. That is the point I was trying to express. Where is the energy stored? (In my OP, I used the term "revealed", but "stored" is better).

 

In the case of kinetic energy, it's stored in motion. Motion such as in a spinning flywheel. If you touch the spinning wheel, your finger feels the shock of the kinetic energy.

 

But if you touch an object with so-called potential energy, you feel no shock. No effect at all in fact.

 

Surely this must show that potential energy isn't really the same kind of thing as kinetic energy.

[swansont]

Thanks zoteman. That is the point I was trying to express. Where is the energy stored? (In my OP, I used the term "revealed", but "stored" is better).

 

In the case of kinetic energy, it's stored in motion. Motion such as in a spinning flywheel. If you touch the spinning wheel, your finger feels the shock of the kinetic energy.

 

But if you touch an object with so-called potential energy, you feel no shock. No effect at all in fact.

 

Surely this must show that potential energy isn't really the same kind of thing as kinetic energy.

 

I know that basic-level descriptions often portray energy in such a way that it is easy to think of it as a substance, but it isn't. It's a property. And in a system with potential energy, one property is that there is a force which is position-dependent and the work that force does is path-independent. The system is in a configuration where the force is going to be able to do work.

 

Potential energy is the work done against a conservative external force. A conservative force allows you to define the potential energy.

 

[math]F = -\nabla{U}[/math]

 

Kinetic energy is work done by the net force. We give it a special name because it's convenient to do so.

 

 

I urge you not to touch any object with a large amount of electrostatic potential energy. You can get a nasty shock.

[Dekan]

 

I urge you not to touch any object with a large amount of electrostatic potential energy. You can get a nasty shock.

 

Thanks Swansont, you made me smile about the electrostatic energy! Touching a charged sphere of a van de Graaff generator, does indeed give a shock. I can testify to that.

 

But electrostatic energy isn't really just potential energy, is it? It's actual energy, residing in all the extra electrons which have been stored in the charged sphere.

 

These extra electrons make an electrostatically charged sphere, physically different from an uncharged one - the charged one contains more electrons.

 

However a sphere charged with gravitational potential energy, doesn't seem physically different in any way from an uncharged one.

 

Or does it contain more gravitons?

[lemur]

However a sphere charged with gravitational potential energy, doesn't seem physically different in any way from an uncharged one.

The same sphere would not push down as hard (i.e. with as much force) if it had less gravitational potential, e.g. on the moon. I think I can safely say that weight is to gravitational potential what charge-voltage is to electrostatic potential. I have to be careful saying this, though, because someone might accuse me of being physics-illiterate and spreading false knowledge.

[mooeypoo]

The same sphere would not push down as hard (i.e. with as much force) if it had less gravitational potential, e.g. on the moon. I think I can safely say that weight is to gravitational potential what charge-voltage is to electrostatic potential. I have to be careful saying this, though, because someone might accuse me of being physics-illiterate and spreading false knowledge.

A good start of avoiding this is to pose things you're uncertain about as a question rather than a statement.

 

 

 

Weight is a force (Gravitational force) and Voltage is an electric potential difference, so in that aspect I'd just be careful in the similar-framing. But in general, I guess you can think of it similarly in terms of conceptual imagining of the effects;

• To get gravitational potential we can use the equation [math]W=\int F \cdot dr[/math] (which leads to mgh on earth)
• To get electric potential we can use the equation [math]V=\int E \cdot dl[/math]

In that aspect, they're similar.

 

Just worth noting also that electric potential will only act on objects with an electric charge while gravitational potential will act on all mass.

 

~mooey

[swansont]

Thanks Swansont, you made me smile about the electrostatic energy! Touching a charged sphere of a van de Graaff generator, does indeed give a shock. I can testify to that.

 

But electrostatic energy isn't really just potential energy, is it? It's actual energy, residing in all the extra electrons which have been stored in the charged sphere.

 

These extra electrons make an electrostatically charged sphere, physically different from an uncharged one - the charged one contains more electrons.

 

However a sphere charged with gravitational potential energy, doesn't seem physically different in any way from an uncharged one.

 

Or does it contain more gravitons?

 

Electrons packed onto the surface of a conductor have potential energy because of their position relative to each other, and that they feel an electrostatic force. That force can do work if the charges are free to move. Gravitational potential energy is no different in that regard. You don't need to have extra charges in order to have electrostatic potential energy. Classically, a proton and an electron will have potential energy, and it will vary depending on how far apart they are.

[DrRocket]

But electrostatic energy isn't really just potential energy, is it? It's actual energy, residing in all the extra electrons which have been stored in the charged sphere.

 

 

Potential energy is actual energy. It is just a convenient name, and not "something that is potentially energy". This illustrates the problem with misinterepreting technical terms in light of the everyday meaning of the words.

 

If you consider relativistic mass, as in [math]E=mc^2[/math] then [math]m[/math] is a reflection of energy and it doesn't matter whether that energy is potential or kinetic. It does matter what reference frame is used to determine either energy or relativistic mass.

[zapatos]

The same sphere would not push down as hard (i.e. with as much force) if it had less gravitational potential, e.g. on the moon. I think I can safely say that weight is to gravitational potential what charge-voltage is to electrostatic potential. I have to be careful saying this, though, because someone might accuse me of being physics-illiterate and spreading false knowledge.

With all due respect as I am sure I am at the low end of scientific literacy on this site...

 

I don't think anyone is picking on you. It just seems to me that you regularly try to convert their highly specific/technical/supported descriptions of nature into a less precise format/language that you prefer to use. Since your format/language is less capable of describing the nuances and detail of nature than theirs, it shouldn't be a surprise that they can only help to a certain degree and that you get results that are not to your satisfaction or accepted by them. Frustrating for all.

 

That being said I learn a lot watching you work through things.

[lemur]

With all due respect as I am sure I am at the low end of scientific literacy on this site...

 

I don't think anyone is picking on you. It just seems to me that you regularly try to convert their highly specific/technical/supported descriptions of nature into a less precise format/language that you prefer to use. Since your format/language is less capable of describing the nuances and detail of nature than theirs, it shouldn't be a surprise that they can only help to a certain degree and that you get results that are not to your satisfaction or accepted by them. Frustrating for all.

 

That being said I learn a lot watching you work through things.

Dekan's post said that he didn't see a different between an object "charged" with gravitational potential and one that wasn't. Thus it seemed pertinent to give a concrete, tangible example; i.e. the force with which the object pushes down against the ground or whatever it is 'resting' on. Since the word, "charged" was used, I thought it would be helpful to consider an analogical expression of 'gravitational pushing' in electric force. My conclusion was that electric charge 'pushes' against an insulator with the amount of voltage it is poised to transmit at the moment the circuit closes. Thus I think it is reasonable to compare weight to voltage, where an obstacle preventing an object from falling impairs gravitational motion in the same way an insulator prevents an electric charge from flowing further within the circuit. In both cases, force is met with resistance and the "equal and opposite reaction" of the resistance is the potential of the impeded kinetic energy (flow). If this reasoning is incorrect, I of course want to hear why, but I see nothing faulty about it, honestly.

Edited June 7, 2011 by lemur

[DrRocket]

Dekan's post said that he didn't see a different between an object "charged" with gravitational potential and one that wasn't. Thus it seemed pertinent to give a concrete, tangible example; i.e. the force with which the object pushes down against the ground or whatever it is 'resting' on. Since the word, "charged" was used, I thought it would be helpful to consider an analogical expression of 'gravitational pushing' in electric force. My conclusion was that electric charge 'pushes' against an insulator with the amount of voltage it is poised to transmit at the moment the circuit closes. Thus I think it is reasonable to compare weight to voltage, where an obstacle preventing an object from falling impairs gravitational motion in the same way an insulator prevents an electric charge from flowing further within the circuit. In both cases, force is met with resistance and the "equal and opposite reaction" of the resistance is the potential of the impeded kinetic energy (flow). If this reasoning is incorrect, I of course want to hear why, but I see nothing faulty about it, honestly.

 

The fact that you honestly see nothing faulty in a paragraph of total gibberish tells the whole story.

 

Nobody can take you from a state of total misunderstanding (honestly less than zero) of elementary physics to a level of comprehension commensurate with that of a college freshman with the resources available on a bulletin board.

 

Buy that physics book and read it.

[mooeypoo]

The fact that you honestly see nothing faulty in a paragraph of total gibberish tells the whole story.

 

Nobody can take you from a state of total misunderstanding (honestly less than zero) of elementary physics to a level of comprehension commensurate with that of a college freshman with the resources available on a bulletin board.

 

Buy that physics book and read it.

 

 

 

 

I support this request.

 

 

lemur, before you can claim to revolutionize the way physicists talk and see concepts, you really should learn how physicsists *ACTUALLY* talk and see those concepts. You seem to have a view of what physics says that is too far from the real deal.

 

I don't quite understand your reluctance to actually learn about the subject you're so keen on criticizing before you continue criticizing it.

 

Are you interested in understanding reality, or are you interested in showing us all you're right despite not having physics education? You don't do much of reality explanation, whether you THINK you do or not.

 

~mooey

[lemur]

The fact that you honestly see nothing faulty in a paragraph of total gibberish tells the whole story.

 

Nobody can take you from a state of total misunderstanding (honestly less than zero) of elementary physics to a level of comprehension commensurate with that of a college freshman with the resources available on a bulletin board.

 

Buy that physics book and read it.

It is not gibberish. You can't keep making these undermining criticisms without reference to anything I said. There is nothing special about you that allows you to insist on the validity of your assessments simply because they're yours. Anyone can call anyone else's post gibberish but it doesn't prove who's right and who's wrong. What is stopping any crackpot from calling anything you post "gibberish" and telling you to go read a physics book?

 

 

[mooeypoo]

It is not gibberish. You can't keep making these undermining criticisms without reference to anything I said. There is nothing special about you that allows you to insist on the validity of your assessments simply because they're yours. Anyone can call anyone else's post gibberish but it doesn't prove who's right and who's wrong. What is stopping any crackpot from calling anything you post "gibberish" and telling you to go read a physics book?

 

 

We can't reference what you say becuse you don't speak an ounce of physics. We are asking that you go over a textbook so we can speak the same language when you criticize.

 

What you're currently doing is criticizing swahili without when you barely know swahili and you do it in a different language. If you want to argue a physicist in their own court, you need to learn what that court involves.

 

 

There's not much more to say, lemur. One person telling you X might have it out for you. Two people? Maybe they both have it out for you. But many people? You might want to take our advice at this point.

 

Get a book and read the physics you criticize. We can't debate you otherwise.

 

~mooey

 

 

[lemur]

We can't reference what you say becuse you don't speak an ounce of physics. We are asking that you go over a textbook so we can speak the same language when you criticize.

 

What you're currently doing is criticizing swahili without when you barely know swahili and you do it in a different language. If you want to argue a physicist in their own court, you need to learn what that court involves.

 

 

There's not much more to say, lemur. One person telling you X might have it out for you. Two people? Maybe they both have it out for you. But many people? You might want to take our advice at this point.

 

Get a book and read the physics you criticize. We can't debate you otherwise.

 

~mooey

 

 

The post in question used adequate terms. Shall I repost it in another thread for sentence-by-sentence criticism? It was not written using any language ureadable to anyone who knows physics or who doesn't for that matter.

[mooeypoo]

Obviously it didn't use proper terms, since multiple people have been telling you for a while now that you're making no physical sense.

 

Instead of insisting you're right, try cooperating for a change and read the subject in question. I can promise you that if it won't help, it definitely won't hurt.

 

We can't really continue like this when you just insist you're right despite everyone.

 

~mooey