What is energy?

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Hello PF:smile:


Up till now i have learned that something that has the ability to do force*displacement is called energy.But what is energy at a microscopic level ?
 

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  • #2
A.T.
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See last paragraph:

Richard Feynman said:
There is a fact, or if you wish, a law governing all natural phenomena that are known to date. There is no known exception to this law – it is exact so far as we know. The law is called the conservation of energy.

It states that there is a certain quantity, which we call “energy,” that does not change in the manifold changes that nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says there is a numerical quantity which does not change when something happens.

It is not a description of a mechanism, or anything concrete; it is a strange fact that when we calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.

It is important to realize that in physics today, we have no knowledge of what energy “is.” We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. It is an abstract thing in that it does not tell us the mechanism or the reason for the various formulas.
 
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jtbell
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  • #4
HallsofIvy
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I don't think it makes sense to talk about energy "at the molecular level". What in the world would the "potential energy of a rock sitting on a cliff" even mean "at the molecular level. Fundamentally, energy is a "bookkeeping" device. Every time we find a situation in which it appears that energy is NOT conserved, we define a new kind of energy to cover the difference!
 

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