The unit used to express energy or work in the field of physics is the joule. The joule is defined as the amount of energy transferred when a force of one newton acts over a distance of one meter. It is a standard unit of measurement in the International System of Units (SI) and is widely used across various scientific disciplines, including thermodynamics, mechanics, and electromagnetism. Understanding joules helps quantify energy changes in different processes, making it crucial for calculations in physics and engineering.