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

PhanthomJay

There are two distinctions to which I refer. I can't speak for all people.
Suppose that a motorized pulley is used to move a crate up an incline. The mechanical energy (definition 2) of the motor/pulley causes work to be done on the system which in turn increases the mechanical energy (definition 1) of the system. Well, what do you think, people, and what do you think, I-c?

I-copeland

So are you saying here that because it is used out of context it is used to mean something completely different, so therefore mechanical energy has two meanings?

PhanthomJay

When i think of Chemical energy, I think of mixing chemicals together; when i think of Electrical energy, I think of powerlines; when i think of Nuclear energy, it's the bomb; when i think of Mechanical energy, I think of engines and machines. Each of these types of energy, and others I have not listed, are capable of producing changes to the kinetic and potential energies of a system, that is, changes to the mechanical energy of a system.

I-copeland

so one type of chemical energy is mechanical and the othe is not...

suneelguptaz

Non conservative forces (dissipative) like friction, viscous etc.

Work done against conservative forces is stored in one way or other. Work done against electrostatic force is stored as electrostatic potential energy, Work done (at constant velocity) against gravitational force is stored as gravitational potential energy, I am trying talk as simple as possible.
But work done against friction is dissipated in the form of heat.

Please read the basic concept of potential energy from some good book. This will help you.

I-copeland

So is chemical energy mechanical and non-mechanical?

I-copeland

Ok makes sense, what others are thier apart from friction?

Oh and my previous q still applies:

suneelguptaz

Mechanical word might have coined in mechanics but if I have to chose between mechanical & mechanical and non-mechanical then I will go with mechanical.

I-copeland

ok so then what energy isn't mechanical?

suneelguptaz

Really wonderful!!! it seems every form of energy falls in this category......
Now I am guessing (unconvinced myself)
Mass Energy???

I-copeland

hey if your noit being sarcastic i'm glad through my learning you learnt something... but is it really true?

suneelguptaz

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

mikelepore

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.

Antiphon

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.)

Woopydalan

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.

Somenath

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.

I-copeland

PhanthomJay are all energies mechanical?