What actually is energy and why is it conserved
Energy is often defined as 'The ability to do work', which is just saying that energy is energy, which is not a very intellectually satisfying answer.
The question of what energy 'is' is a fairly philosophical question. Consider the following;
In order to describe what something 'is' we have to describe it in terms of more basic elements, a molecule are two or more atoms bonded together, an atom is one or more electrons bonded with a nucleus, a nucleus consists of one or more nucleons, a nucleon consists of quarks so on and so forth.
Eventually one hits the wall when one comes to energy, it cannot be described in terms of more basic elements, because there are no more basic elements. That is why textbook definitions essentially describe energy in terms of itself.
As to why it is conserved, no one can explain fundamentally why energy is conserved, only that the in the countless observations we have made over the centuries no one has ever observed energy to be either created or destroyed.
Thanks was just something that puzzled me a little as i had never had a firm definition of energy or reason why it is conserved and thought that maybe missed something
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