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I am not able to understand the second paragraph well. Please elaborate me anybody

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  • $\begingroup$ Please be more specific on the sentence or sentences that you can't interpret. $\endgroup$ – David White Jan 26 at 6:24
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It is a typical and unfortunately quite popular way of introducing the concept of energy in a very obscure way. The problem with such an approach to the concept of energy is that one is trying to convey one of the most important feature of the concept, before even trying to provide a hint about what should be measured or calculated. Quite a pity for an experimental science!

I strongly advise you to skip for the moment that paragraph, go ahead, try to grasp a first idea about the content of the whole chapter, and then you can go back the this second paragraph with some possibility of assigning some meaning to it.

Just to provide you a trailer of what you could find in the next pages, presumably the author will introduce a couple of scalar quantities, named potential and kinetic energy, both depending on the instantaneous configuration of a system and it will be shown that any change of each of them is always accompanied by an opposite change of the other. Probably some chapters after, it will be shown that the same concept may be extended to deal with much more complex physical systems like fields, macroscopic objects with invisible atomic elementary units etc. In my opinion, anticipating so much the result is not very useful from a pedagogical point of view.

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  • $\begingroup$ 's as you have told me I have gone through the whole chapter and studied about different forms of energy and few laws. But they haven't mentioned about the fact that what is the significance of any body having energy in itself. Is it only that it possess energy so it can transfer it through work? And as mentioned in the paragraph about the scheme by which they were able to quantify energy further in the topic nothing is mentioned about that scheme any more. $\endgroup$ – Rifat Safin Jan 28 at 11:09
  • $\begingroup$ @RifatSafin Is it a chapter on mechanical energy or thermodynamical energy? $\endgroup$ – GiorgioP Jan 28 at 12:09
  • $\begingroup$ Mechanical energy $\endgroup$ – Rifat Safin Jan 29 at 4:06
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The second paragraph tells us about how abstract the concept of energy is but also how naturally connected it is to the universe. The author is trying to convey that energy is some sort of a number that one can calculate using certain formulas (like $\frac 12 mv^2$ for Kinetic energy or $mgh$ for Gravitational Potential energy) for objects in the universe, and that it has many forms in nature, but for some reason quite unknown to us, nature always tends to keep the total energy of the universe constant. You can convert energy from one form to the other, but never create or destroy it. This is what the author refers to as "wonderful property of our universe". Formally it is called - The principle of conservation of energy.

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