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OfflineSammysong
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What is energy?
    #19177749 - 11/23/13 05:11 AM (10 years, 2 months ago)

I'm hoping that a discussion about the nature of the physical quantity referred to as "energy" might illustrate how surprisingly diverse and abstract this concept is and lead on to a discussion of other apparently abstract, yet arguably useful, concepts in science.

Note: For simplicity and brevity, I don't go as far here as the more advanced concept of mass/energy equivalence. I'm only interested in discussing a limited, classical conception of energy. If the discussion digresses on to the usual arguments about modern physics concepts, I don't believe we will achieve much. I think there is a great deal to be said for taking one step at a time.

---

Traditionally, we are taught that energy manifests itself in various different forms. For example:

Kinetic Energy. When an object is moving, we take the mass and speed of that object, stick them into a little equation (e.g. 1/2 X mass X speed X speed) and claim that the resulting number is a quantity called "energy".

Potential Energy:

Gravitational Potential Energy. When an object is in a gravitational field, we take its mass, its position within the field, and the strength of the field, stick them into another little equation and claim that that resulting number is also a quantity called "energy".

Electromagnetic Potential Energy. When an electrically charged object is in an electromagnetic field. Similar to gravitational potential energy. Having a position in any kind of conservative force field means you have potential energy. Or so the standard story goes.

Chemical Potential Energy.

Essentially the same as electromagnetic potential energy because it's generally about the configuration and relative positions of the electrically charge bits of molecules.

---

The key interesting point here is that there is no obvious, immediate, intuitive reason to think that, for example, gravitational P.E is the same "thing" as K.E. In fact, it's far from obvious that either of these two quantities should be regarded as "things" at all. So why are they?

If I take an everyday ordinary physical object and move it from one place to another, we do have a direct, visceral, intuitive sense that it is the same object - the same "thing". For that reason, we have an intuitive sense of the concept that might be called "conservation of matter". i.e. we can't make objects spontaneously appear or disappear. We naturally notice the invariant properties when an object is moved.

But for something like energy, it's much less obvious. What has been observed, and gathered over many years, is that the quantities defined by certain equations appear to always be invariant. i.e. they don't change. They are "conserved". As soon as we discover a quantity which has this property of invariance, it starts to be useful to regard it as a "thing". The "thing" in this case is energy.

So, take the simple, classical equation for the energy of a moving object (kinetic energy):

Energy = 1/2 X mass X speed X speed

Then take the equation for the energy of an object in a uniform gravitational field (i.e. where everything is pulled in the same direction with the same force, as it is approximately in a small volume near the surface of the Earth):

Energy = g X mass X height

Where "g" is a number that represents the strength of gravity - the force experienced by each unit of mass. (About 10 Newtons of force on every kilogram, near the Earth).

At first glance, the two quantities that you get by working out the results of these two equations are completely unrelated. But since it turns out that an increase in one is always accompanied by a corresponding decrease in the other, we tend to think of them as representing some "thing" which has somehow been moved around. Almost like an object.

---

The above is all basic high school physics with nothing to do with any fancy modern ideas like QM or Relativity or mass/energy equivalence. I deliberately haven't gone into much detail and stuck to the simplest examples in the hope of making the issues accessible to as wide an audience as possible. Yet, even at this mundane level, when you think about it, the concepts involved are strange. Strange concepts are available to all!

Are readers happy or unhappy with the energy concept, in the limited sense described here? (I.e. not getting into any more advance concepts yet).

If unhappy, why? Do you think that this energy concept doesn't deserve the status of "thing"? Do you think it's all mathematical smoke and mirrors? Do you think that this whole concept of energy is un-useful?


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InvisibleMr Person
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Re: What is energy? [Re: Sammysong] * 1
    #19178099 - 11/23/13 08:58 AM (10 years, 2 months ago)

I can conceptualize energy when explained in terms of movement, and measurements of that movement.  So heat and electricity are the movements of atoms and electrons respectively.  Kinetic energy is obvious, and chemical energy is the interaction of molecules exchanging their pieces.

It starts to break down for me when you get to the fundamental forces.  I understand that these exist mathematically, but I have trouble picturing them when described as "things".  With photons, for example, I can't wrap my head around the same energy I associate with motion existing as a non-physical particle (or a wave-- of what?). 

With gravity it seems that popular science teaches us to conceive of it as being like rolling down a hill of space-time due to the curvature caused by the presence of mass.  I guess that kind of makes sense until I start thinking about space and the paradox of vacuum and nothingness, which gives me trouble when I try to think of space as a fabric.

I'm ashamed to say that magnetism is still magic to me no matter how much it's explained.  I just don't understand how the basic impulse to move is created by the alignment of electrical charges, though once those charges start to move I get how electricity works.  It's the same with the strong and weak force.  I understand them as movements of nucleons and protons towards and away from one another, but I don't understand what generates that movement.


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InvisibleIcelander
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Re: What is energy? [Re: Mr Person] * 1
    #19178137 - 11/23/13 09:20 AM (10 years, 2 months ago)

Don't be ashamed.  I don't understand hardly anything about anything.  Beyond DA that is. :lol:


--------------------
"Don't believe everything you think". -Anom.

" All that lives was born to die"-Anom.

With much wisdom comes much sorrow,
The more knowledge, the more grief.
Ecclesiastes circa 350 BC


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InvisibleOrgoneConclusion
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Re: What is energy? [Re: Icelander]
    #19178158 - 11/23/13 09:28 AM (10 years, 2 months ago)



You are indeed the Deputy District Attorney here.


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InvisibleIcelander
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Re: What is energy? [Re: Sammysong]
    #19178165 - 11/23/13 09:30 AM (10 years, 2 months ago)

What is energy?

That's an easy one.  It's something I used to have a lot of.  :drunkdriver:


--------------------
"Don't believe everything you think". -Anom.

" All that lives was born to die"-Anom.

With much wisdom comes much sorrow,
The more knowledge, the more grief.
Ecclesiastes circa 350 BC


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InvisibleIcelander
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Re: What is energy? [Re: OrgoneConclusion]
    #19178168 - 11/23/13 09:31 AM (10 years, 2 months ago)

Quote:

OrgoneConclusion said:


You are indeed the Deputy District Attorney here.



:lol:

:mad2:


--------------------
"Don't believe everything you think". -Anom.

" All that lives was born to die"-Anom.

With much wisdom comes much sorrow,
The more knowledge, the more grief.
Ecclesiastes circa 350 BC


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InvisibleOrgoneConclusion
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Re: What is energy? [Re: Icelander]
    #19178170 - 11/23/13 09:32 AM (10 years, 2 months ago)

Sure you are not talking about hair?


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InvisibleIcelander
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Re: What is energy? [Re: OrgoneConclusion]
    #19178183 - 11/23/13 09:37 AM (10 years, 2 months ago)

That too. :sad:  Actually I still have a lot but it's all thin and old man like.  :justnotright:


--------------------
"Don't believe everything you think". -Anom.

" All that lives was born to die"-Anom.

With much wisdom comes much sorrow,
The more knowledge, the more grief.
Ecclesiastes circa 350 BC


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InvisibleOrgoneConclusion
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Re: What is energy? [Re: Icelander] * 1
    #19178195 - 11/23/13 09:40 AM (10 years, 2 months ago)



Try activating your ear chakras. :levitate:


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InvisibleIcelander
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Re: What is energy? [Re: OrgoneConclusion]
    #19178315 - 11/23/13 10:16 AM (10 years, 2 months ago)

I just got told in PM that I look like Clint Eastwood but I think my dad looked even more like him.


--------------------
"Don't believe everything you think". -Anom.

" All that lives was born to die"-Anom.

With much wisdom comes much sorrow,
The more knowledge, the more grief.
Ecclesiastes circa 350 BC


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InvisibleRepertoire89
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Re: What is energy? [Re: Icelander]
    #19178384 - 11/23/13 10:31 AM (10 years, 2 months ago)

Quote:

Icelander said:
I just got told in PM that I look like Clint Eastwood but I think my dad looked even more like him.




You look like a near twin of my dad, threw me off for a good minute :lol:


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InvisibleIcelander
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Re: What is energy? [Re: Repertoire89]
    #19178452 - 11/23/13 10:47 AM (10 years, 2 months ago)

Icelander - All things to all people -


--------------------
"Don't believe everything you think". -Anom.

" All that lives was born to die"-Anom.

With much wisdom comes much sorrow,
The more knowledge, the more grief.
Ecclesiastes circa 350 BC


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InvisibleLunarEclipse
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Re: What is energy? [Re: Icelander]
    #19178475 - 11/23/13 10:55 AM (10 years, 2 months ago)

Quote:

Icelander said:
Icelander - All things to all people -




You really do need a new schtick.


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Anxiety is what you make it.


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InvisibleIcelander
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Re: What is energy? [Re: LunarEclipse]
    #19178556 - 11/23/13 11:27 AM (10 years, 2 months ago)

I'm too old and tired to work anything up.:sad:  I'm just hoping someone still believes the old one.


--------------------
"Don't believe everything you think". -Anom.

" All that lives was born to die"-Anom.

With much wisdom comes much sorrow,
The more knowledge, the more grief.
Ecclesiastes circa 350 BC


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InvisibleRepertoire89
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Re: What is energy? [Re: Icelander]
    #19178580 - 11/23/13 11:36 AM (10 years, 2 months ago)

Quote:

Icelander said:
I'm too old and tired to work anything up.:sad:  I'm just hoping someone still believes the old one.




Thor? I'm more a fan of Tartarus


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InvisibleLunarEclipse
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Re: What is energy? [Re: Icelander]
    #19178592 - 11/23/13 11:41 AM (10 years, 2 months ago)

Quote:

Icelander said:
I'm too old and tired to work anything up.:sad:  I'm just hoping someone still believes the old one.




Not me.  I'm at the top of my game.



--------------------
Anxiety is what you make it.


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InvisibleDieCommie

Registered: 12/11/03
Posts: 29,258
Re: What is energy? [Re: LunarEclipse]
    #19178696 - 11/23/13 12:09 PM (10 years, 2 months ago)

There is absolutely obvious reason all these quantities are considered energy.  The reason those quantities are "claimed" to be energy is because they have the units of energy.  The units of energy are kg m^2/s^2, if the quantity you are considering has those units then its energy.  Whether you want it to be considered a "thing" or not is a matter of taste and makes no difference to any theory.

The fact that energy is observed to be conserved can be directly entailed from "Noethers theorem".  Per noether's theorem it is shown that time symmetry in physical laws necessitates energy conservation.  Thats some nice philosophical meat.  If we accept that the laws of physics don't change over time then we have to accept that conservation of energy holds.


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InvisibleLunarEclipse
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Re: What is energy? [Re: DieCommie] * 1
    #19178744 - 11/23/13 12:22 PM (10 years, 2 months ago)

Quote:

DieCommie said:
There is absolutely obvious reason all these quantities are considered energy.  The reason those quantities are "claimed" to be energy is because they have the units of energy.  The units of energy are kg m^2/s^2, if the quantity you are considering has those units then its energy.  Whether you want it to be considered a "thing" or not is a matter of taste and makes no difference to any theory.

The fact that energy is observed to be conserved can be directly entailed from "Noethers theorem".  Per noether's theorem it is shown that time symmetry in physical laws necessitates energy conservation.  Thats some nice philosophical meat.  If we accept that the laws of physics don't change over time then we have to accept that conservation of energy holds.




Thats a fancy way of saying "you don't have a clue".  Nice philosophical meat.

Ah Bologna.


--------------------
Anxiety is what you make it.


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InvisibleIcelander
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Re: What is energy? [Re: LunarEclipse]
    #19178764 - 11/23/13 12:27 PM (10 years, 2 months ago)

Quote:

LunarEclipse said:
Quote:

Icelander said:
I'm too old and tired to work anything up.:sad:  I'm just hoping someone still believes the old one.




Not me.  I'm at the top of my game.







Just finished listening to Neil Young's Psychedelic Pill LP.  How's that for synchronicity.


--------------------
"Don't believe everything you think". -Anom.

" All that lives was born to die"-Anom.

With much wisdom comes much sorrow,
The more knowledge, the more grief.
Ecclesiastes circa 350 BC


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InvisibleLunarEclipse
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Re: What is energy? [Re: Icelander]
    #19178773 - 11/23/13 12:31 PM (10 years, 2 months ago)



--------------------
Anxiety is what you make it.


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