First Law of Thermodynamics Explained

The first law of thermodynamics is a core principle governing energy transfer and transformation within physical systems.

Principle of Conservation

This law fundamentally states that energy in an isolated system remains constant over time. It cannot be created or destroyed, only changed from one form to another.

• Energy Conversion: The law highlights that energy can be converted between different forms, such as heat, work, and internal energy.
• System Energy: For any process, the change in the internal energy of a system ($\Delta U$) is equal to the heat added to the system ($Q$) minus the work done by the system ($W$). The mathematical expression is:

  $\Delta U = Q - W$

Relation to Conservation Laws

The first law of thermodynamics is essentially an expression of the conservation of energy applied to thermodynamic processes.

Other conservation laws, like the conservation of mass or momentum, are fundamental but are described by different physical laws (e.g., Newton's laws for momentum, principles of mass continuity for mass). The increase in entropy relates to the second law of thermodynamics, not the first.