The conceptual frameworks that describe the universe are built upon two fundamental entities. One is the capacity to perform work, manifesting in various forms such as kinetic, potential, thermal, and electromagnetic. The other comprises the substance of the physical world, possessing mass and occupying space. These two entities are interconnected, with one capable of being converted into the other under specific conditions, as described by established scientific principles.
Understanding these foundational elements is critical for numerous scientific disciplines. This understanding underpins technologies ranging from power generation to materials science. Historically, the precise relationship between these entities was not always clear, with significant advancements in physics during the 20th century providing greater clarity and a more unified perspective. This historical perspective allows us to improve our current technologies.