Which statement best identifies the law stating that energy in the universe is constant?

• A. Law of Conservation of Energy
• B. Energy Cannot Be Created or Destroyed
• C. First Law of Thermodynamics
• D. Newton's Third Law

Answer: (C)

Energy cannot be created or destroyed; it can only be transformed, so the total energy remains constant. In thermodynamics, this universal balance is captured by the First Law of Thermodynamics, which formalizes energy conservation for any process in terms of heat, work, and internal energy. When we view the universe as an isolated system, its total energy stays constant, aligning with this law. While the general idea is also described by a conservation law or the statement that energy can’t be created or destroyed, the standard thermodynamics term for this principle is the First Law, making it the best label here. Newton's Third Law, by contrast, deals with equal and opposite forces and isn’t about energy conservation.