law of conservation of energylaw

In the mid-19th century, several scientists independently concluded that heat is not a mysterious fluid but a form of particle motion. Julius Mayer, observing the color of sailors' blood, noticed a connection between the body's work and heat. James Joule, through precise experiments, measured how much heat mechanical work produces. Hermann von Helmholtz formalized it into a coherent theory. The law of conservation of energy states: in an isolated system, total energy — the sum of kinetic, potential, thermal, and other forms — is constant. It's like a family budget: income and expenses can change form, but the total amount in the account is preserved if no external source intervenes.

The law says: in a closed system (where nothing enters from outside and nothing leaves), the total amount of energy is always the same. Energy can change from one form to another — like water poured from a jug into a glass remains water. A swing: at the top point it is motionless and full of potential energy (position energy), at the bottom it rushes — kinetic energy (motion energy) is maximum, and the sum of these two energies is constant if friction is ignored.

The law of conservation of energy is a fundamental principle of physics, stating that the total energy of a closed system remains constant over time. Energy is neither created nor destroyed, but only transformed from one form to another. In classical mechanics, this is expressed as the constancy of the sum of kinetic and potential energy: E = K + U = const. In thermodynamics — by the first law: ΔU = Q − W, where the change in internal energy equals the heat added minus the work done by the system. Noether's theorem links this law to symmetry: the invariance of physical laws with respect to time translation leads to energy conservation.