What exaclty is Mechanical Energy? Or more specificaly potential energy (the subset)

  • Thread starter I-copeland
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  • #26
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ok so then what energy isn't mechanical?
 
  • #27


Really wonderful!!! it seems every form of energy falls in this category......
Now I am guessing (unconvinced myself)
Mass Energy???
 
  • #28
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hey if your noit being sarcastic i'm glad through my learning you learnt something... but is it really true?
 
  • #29


hey if your noit being sarcastic i'm glad through my learning you learnt something... but is it really true?
:approve:
It is true that I have learnt. I was (and still I am) awestruck by the thought that every form of energy is ..... ultimately ... mechanical energy.
I am also thinking at nuclear level... (regarding mass energy...)
Great exercise I-C
 
  • #30
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Another nonconservative force is the interaction in an electrical conductor that results in electrical resistance. In some ways it acts similar to friction, in the sense that it prevents electrons from achieving huge accelerations, and energy gets dissipated in the form of heat.

The indicator is that energy comes out of the system in any form -- light, sound, heat. When two billiard balls collide you can hear a sound. Since sound came out, the collision must have been inelastic, even if it was approximately elastic. Therefore the contact force between them was nonconservative, or dissipative. We won't call it kinetic friction since they bounced instead of sliding, but it was nonconservative just the same. Also, you may have produced microscopic cracks in the billiard balls. If there is structural damage then the force is dissipative. The temperature of the billiard balls has been raised perhaps a millionth of a degree. If you generated heat then the force was dissipative.
 
  • #31
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There in only nuclear, electromagnetic and gravitational.

All mechanical potential energy is electromagnetic (stress, chemical) or gravitational (water wheel etc.)

Elastic can be a mix of the two. When you hang a bowling ball on a bungee cord it's gravitational PE that went into elastic (electromagnetic.)
 
  • #32
member 392791


Isn't mechanical energy just the addition of kinetic energy and potential energy? This definition doesnt imply the potential energy has to be chemical, electrostatic, etc. Seems like just a name to me.
 
  • #33
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Potential energy always has a source force field (nuclear/gravitational/electromagnetic). When we say that work is done, we should remember that it is only a mathematical quantity which is so defined that it can be equated with the change in Kinetic Energy.

The expressions ∫F.ds can be obtained from 1/2mv2 in conservative force field.

When mechanical energy changes into thermal energy, we have to introduce J as multiplicative factor to obtain the heat generated. But in that case too we say that kinetic energy transforms into thermal energy. Actually they are shown to be equal by some transformation rule.
If you hit a thing by a hammer, the Kinetic energy of hammer sets the air in motion and we hear a sound. The energy is still mechanical.
 
  • #34
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PhanthomJay are all energies mechanical?
 
  • #35
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Potential energy always has a source force field (nuclear/gravitational/electromagnetic). When we say that work is done, we should remember that it is only a mathematical quantity which is so defined that it can be equated with the change in Kinetic Energy.

The expressions ∫F.ds can be obtained from 1/2mv2 in conservative force field.

When mechanical energy changes into thermal energy, we have to introduce J as multiplicative factor to obtain the heat generated. But in that case too we say that kinetic energy transforms into thermal energy. Actually they are shown to be equal by some transformation rule.
If you hit a thing by a hammer, the Kinetic energy of hammer sets the air in motion and we hear a sound. The energy is still mechanical.
Whats ur point?
 
  • #36
PhanthomJay
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PhanthomJay are all energies mechanical?
No. But when any type of energy ...be it chemical, nuclear, or (heaven forbid) mechanical energy (definition 2)...is transfered into or out of the system, it changes the mechanical energy (definition 1) of the system. This follows from conservation of energy law, dE + dU + dK = 0, where dE represents the energy transfered into or out of the system from work done by non-conservative forces.
 
  • #37
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i don't understand.
Basically I've heard chemical energy is classified potential and so i want to know (following logic) if it is mechanical and if not then the this could cause the Professor of Logic to spit out his drink.
 
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  • #38
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Chemical energy libeated in a reaction is equivalent to the change in Potential energy due to the force of attraction among the atoms.
 
  • #39
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Whats ur point?
I mean the transformation relations between Potential and other energies are so designed that they seem to be equal.
 
  • #40
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I mean the transformation relations between Potential and other energies are so designed that they seem to be equal.
I see, well I'm not inquiring if they're equal but if the energetic classification for chemical energy is mechanical? Jolly good.
 
  • #41
member 392791


Energy is energy is energy? It's all the same concept, just manifests itself in different phenomenons, right?
 
  • #42
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Chemical energy libeated in a reaction is equivalent to the change in Potential energy due to the force of attraction among the atoms.
So it is mechanical...
 
  • #43
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Energy is energy is energy? It's all the same concept, just manifests itself in different phenomenons, right?
U call yourself a scientist!!??
 
  • #44
member 392791


No, I'm actually curious about the answer to your question, but I'm just basing my idea strictly on the definitions provided by wikipedia and how I interpret them. I have pondered myself as to what mechanical energy is, and this is what is provided:

''In physics, mechanical energy is the sum of potential energy and kinetic energy present in the components of a mechanical system.''

Now, this statement doesn't give any definition as to what a mechanical system is, so I wikipedia that and find:

''A mechanical system manages power to accomplish a task that involves forces and movement''

Ok, so in all the previous phenomenon discussed (chemical energy, electrical energy, etc) there are forces involved and movement, so I am prone to believe, based strictly on these definitions, that they (chemical or electrical phenomenon) are also mechanical systems. If someone reputable is able to tell me otherwise, I am all ears. That is why I joined this discussion, whether to confirm my thoughts or for them to be ripped to shreds is indifferent to me as long as I learn what it actually means.
 
  • #45
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dude! me to.
 
  • #46
Doc Al
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Ok, so in all the previous phenomenon discussed (chemical energy, electrical energy, etc) there are forces involved and movement, so I am prone to believe, based strictly on these definitions, that they (chemical or electrical phenomenon) are also mechanical systems
When we talk about 'mechanical energy' we usually mean energy due to an object's motion (kinetic energy) and position (potential energy). The kinetic energy meant here is macroscopic kinetic energy--due to the object's motion as a whole, not its internal molecular motion. Similarly, the potential energy included in 'mechanical energy' is due to the object's macroscopic position--it excludes all sorts of internal energy such as chemical energy.
 
  • #47
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So mechanical energy is used to describe only what its name implies, mascroscopic objects? No electrons for electrical energy (because the electrons do have mass)?
 
  • #48
Doc Al
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So mechanical energy is used to describe only what its name implies, mascroscopic objects?
Usually, yes. But it depends on the context.
No electrons for electrical energy (because the electrons do have mass)?
When the electron is the object, then you can consider its electrostatic potential energy (when with another charged particle) as part of the mechanical energy of the system.

But if your system is a ball throw up in the air, then all that matters is its macroscopic kinetic energy and the gravitational PE when considering its mechanical energy. (At least that is the usual context.)
 
  • #49
Drakkith
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So mechanical energy is used to describe only what its name implies, mascroscopic objects? No electrons for electrical energy (because the electrons do have mass)?
In any macroscopic non-electrical machine the electrons are too small to matter, so any energy they have isn't included. In electrical machines, which specifically deal with moving electrons, this is obviously different. For mechanical energy, think in terms of classical machines and what we build from them. Something like a clock that uses a pendulum and weights is pure mechanical energy, no electrical or chemical.
 
  • #50
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So u get "macroscopic mechanical energy" and "microscopic mechanical energy"?
 

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