What exactly is energy?

[The_Believer1]

Hello  guys!

I am confused about the concept of energy. I have read that energy is the ability to do work. But this definition of energy seems incomplete to me. I wonder what exactly is energy. Is it a physical thing? can we see  it? touch it?  does it exist in matter as an invisible thing? Also the law of conservation of energy says that energy can never be created nor destroyed. So what is this thing called energy that can't be created or destroyed?. Can anyone please clarify this concept to me? It would be of great help. Thanks!

[Strange]

Energy is a party of "things" (from subatomic particles to complete systems). I don't know if the ability to do work definition is complete, but it is pretty good. Other definitions are likely to be a bit vague: "it is a property we can measure that is conserved when things interact".

And, strictly, energy isn't conserved, but mass-energy is because we can convert energy tombs and mass to energy.

[Country Boy]

 I like to think of "energy" as a "book-keeping device".   We have the "kinetic energy" but then define "potential energy" so that as "kinetic energy" decreases, we can still say that "total energy" stays the same.  But as soon as you introduce friction, "kinetic energy" and "potential energy" are not enough so we introduce "heat energy" to balance the equation.  Every time we have a situation where energy does not seem to be conserved, we introduce another kind of energy!

[swansont]

52 minutes ago, HallsofIvy said:

 I like to think of "energy" as a "book-keeping device".   

Yes. It's a thing that doesn't change even when you have time translation, so if you can track all the different forms of energy, it will be the same from one time to the next. i.e. it's conserved. Telling people it's just book-keeping is not prone to enthusiasm about the subject, though.

 

2 hours ago, The_Believer1 said:

Hello  guys!

I am confused about the concept of energy. I have read that energy is the ability to do work. But this definition of energy seems incomplete to me. I wonder what exactly is energy. Is it a physical thing? can we see  it? touch it?  does it exist in matter as an invisible thing? Also the law of conservation of energy says that energy can never be created nor destroyed. So what is this thing called energy that can't be created or destroyed?. Can anyone please clarify this concept to me? It would be of great help. Thanks!

It's not a physical substance. It's a property of things, i.e. it's a concept. (Like color or height. Being red or tall are not physical things, and you can't touch them, but the physical thing can be red, or tall)

[MigL]

I've often seen the description " Energy is the ability to do work ", and I know Mordred is fond of that description.
However, every time we make use of this energy to do work, some of this property of the system is converted to a non-useable form of energy.
This entropy, although still there, is no longer able to do work.

So I don't know either if the ability to do work is an apt ( or total ) description.
Any insights, Swans ?

[The_Believer1]

1 hour ago, swansont said:

It's not a physical substance. It's a property of things, i.e. it's a concept. (Like color or height. Being red or tall are not physical things, and you can't touch them, but the physical thing can be red, or tall)

 

The law of conservation of energy says that energy can not be created or destroyed but changed from one form into another or transferred from one object to another. By this definition it does not seem energy is just a property of things, but a real thing that exists in the universe. What do you think?

Edited October 19, 2017 by The_Believer1

[studiot]

2 hours ago, The_Believer1 said:

 

The law of conservation of energy says that energy can not be created or destroyed but changed from one form into another or transferred from one object to another. By this definition it does not seem energy is just a property of things, but a real thing that exists in the universe. What do you think?

I think that energy conservation appears in many guises, but only works if you chose the appropriate version and apply it corrrectly.

I also think that energy is not a substance that can be isolated from a body or passed directly to another body.

I am glad you acknowledge that there are various forms of energy, but beware they are not absolute.

Here is a question for you to ponder.

Water is impounded behind a dam 75 metres in height.

A pipe leads water from the bottom of the dam through a turbine to a discharge pond.

Thus the potential energy in the impounded water does work operating the turbine and in turn an electricity generator.

It is easy to calculate the maximum available (potential) energy of the water in realation to the height of the dam.

Or is it?

Suppose I now tell you that the pipe leads 6 kilometres down the valley, a further dop in height of 150 metres, before it reaches the turbine.

The dam and the source lake are the same as before but what is now the potential energy?

As a matter of interest, you have called yourself the Believer.

What exactly is it you believe?

Science is not about belief.

Edited October 19, 2017 by studiot

[Vmedvil]

It is definitely a property or otherwise if it were a physical thing you would see a "Energy Particle" without it being bound into something else like a force for instance we don't see a Energy wave, we see a Electromagnetic Wave, energy being the property of that Electromagnetic wave.

Edited October 19, 2017 by Vmedvil

[Mordred]

10 hours ago, MigL said:

I've often seen the description " Energy is the ability to do work ", and I know Mordred is fond of that description.

 

  Indeed that very definition has withstood the test of time. If there is any definition that never changed since its application via Newtons laws its this one.

 More to the point fond of it because when teaching, one should stick with the proper definitions. (For one thing, you remind them of the kinematic lessons from earlier studies in school.) 

 Here is some definitions from my 1919 physics book I happened upon. Energy " ability to perform work" (unchanged from today)

Potential energy "Energy of position"

kinetic energy "Energy of motion"

I particularly liked how simply yet accurately expressed the latter two are. Yet apply accurately under any physics treatment. In all my studies of any topic  those definitions apply. Particularly since every interaction can modelled via "action" and displacement.

  "Work" also works well when understanding the meaning of mass, as the above defintions arose from f=ma.

In this book from 1919 "Work : the quantity obtained when we multiply the distance in the direction of the force through which it acts". 

Ie any vector quantity. Certainly shows the "Property" aspects mentioned above even then...Side note pricetag of textbook one dollar. Lol don't I wish 

Edited October 20, 2017 by Mordred

[The_Believer1]

9 hours ago, studiot said:

I think that energy conservation appears in many guises, but only works if you chose the appropriate version and apply it corrrectly.

I also think that energy is not a substance that can be isolated from a body or passed directly to another body.

As a matter of interest, you have called yourself the Believer.

What exactly is it you believe?

Science is not about belief.

If energy can not be passed directly to another body then according to quantum mechanics, why does an electron absorb energy to jump from a lower state to higher state and release energy to fall to lower state. If an electron releases and absorbs energy then it must be a substance or else how can something be released or absorbed?

And regarding your question about what I believe is a matter of a different topic altogether. But since you want to know then I must tell you what I believe. I believe the sun will rise tomorrow again. I believe I will reach my destination when I get into my car. I believe I will be alive for many years to come and that's the reason why I make plans for the future. I believe science will one day find, if not all but many of the answers to the questions of the origin of life and the universe. Everything starts with a belief. A belief to know the truth, to reach a conclusion, to find something, to go somewhere, to meet someone or do something. Everything is based on belief in the first place and this belief is what makes us humans move forward in life. So that's what I believe.

So do you believe?

Edited October 20, 2017 by The_Believer1

[Silvestru]

The_Believer1 I believe you should be a writer for rom-coms or a preacher. I see some real talent. 

[swansont]

15 hours ago, The_Believer1 said:

The law of conservation of energy says that energy can not be created or destroyed but changed from one form into another or transferred from one object to another. By this definition it does not seem energy is just a property of things, but a real thing that exists in the universe. What do you think?

If it was a substance we should be able to isolate it. Nothing ever appears as just energy, though. It's not the only physics property, either. There's momentum, angular momentum, entropy and more. None of those work as physical substances, either.  

3 hours ago, The_Believer1 said:

If energy can not be passed directly to another body then according to quantum mechanics, why does an electron absorb energy to jump from a lower state to higher state and release energy to fall to lower state. If an electron releases and absorbs energy then it must be a substance or else how can something be released or absorbed?

An electron jumps to an excited state because of some interaction with a particle that has energy. Such as a photon being absorbed, or a collision with an electron or an atom. It jumps back down in a similar fashion — releasing a photon, or by the atom interacting with a neighboring atom.

 

[studiot]

4 hours ago, The_Believer1 said:

If energy can not be passed directly to another body then according to quantum mechanics, why does an electron absorb energy to jump from a lower state to higher state and release energy to fall to lower state. If an electron releases and absorbs energy then it must be a substance or else how can something be released or absorbed?

And regarding your question about what I believe is a matter of a different topic altogether. But since you want to know then I must tell you what I believe. I believe the sun will rise tomorrow again. I believe I will reach my destination when I get into my car. I believe I will be alive for many years to come and that's the reason why I make plans for the future. I believe science will one day find, if not all but many of the answers to the questions of the origin of life and the universe. Everything starts with a belief. A belief to know the truth, to reach a conclusion, to find something, to go somewhere, to meet someone or do something. Everything is based on belief in the first place and this belief is what makes us humans move forward in life. So that's what I believe.

So do you believe?

A lengthy discussion about belief would be off topic here, but thank you for your reply I find it perfectly reasonable.

The topic of this thread is energy and energy conservation.

I was disappointed that you put less effort into reading that part of my post and missed several vital points, or at least you did not acknowledge them.

I think the best way to achieve an understanding of energy is to include some historical material since the history of the subject has left us with some mixed up terminology often due to historical misunderstandings such as the (incorrect) belief that heat energy is a substance they called caloric. It took the best part of a century to dispel this notion.

It should be noted that Newton did not work in terms of energy and energy laws. He discussed something which we now called momentum.
Energy did not start to surface till the century following Newton, and conservation a century after that.

There is also more to Work and its relationship to energy than has so far been presented here.

I am quite happy to offer a reasoned development of these topics, but only if you will take more notice than you did of my first post since the production would involve significant effort on my behalf and perhaps yours. Understanding is more than belief, but does require this effort.

 

@Mordred.

1919 Physics huh? Youngster! No wonder your avatar looks more sprightly than mine.

 

 

[Mordred]

Lol, the book is one of my favourites, goes into a decent array of topics including the basics of refrigeration and equipment designs at that time..

The atom in this book simply has proton and electron. The Neutron being discovered later.

[Phi for All]

!

Moderator Note

Pet theory response and replies split off to here.

 

[DimaMazin]

Maybe energy is ability to change space/time or force fields. Even photon has potentiale ability to change space/time.