The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. This means that the total energy in a closed system remains constant. For example, when you burn fuel in a car, the chemical energy stored in the fuel is converted into kinetic energy, allowing the car to move. This law is often summarized by the equation: ΔU = Q - W, where ΔU represents the change in internal energy, Q is the heat added to the system, and W is the work done by the system. Understanding this principle is crucial in fields like physics, engineering, and chemistry.