Energy as a silent accountant
Energy is perhaps the strangest concept in all of classical physics. It cannot be seen, cannot be touched, and does not correspond to any “thing”. Yet there is no process in nature whose books fail to balance. Every joule transferred must be recorded in some column of the ledger: kinetic, potential, thermal, chemical, electrical… Feynman, in his Lectures (Feynman, Leighton and Sands 1963), says that energy is like the number of pieces in a certain game: we may not know what they are, but if we count before and after every move we always find the same number. Conservation of energy is not a law we deduce from experience: it is experience itself that forces us, in every new phenomenon, to search for a new column of the ledger to add.
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Topics: Work and energy Concepts: Conservation of mechanical energy
Related exercises: Worked exercise — apple and spring · Problem — Block on a frictionless incline · Problem — Spring compressed by a block