According to conservation of <answer>energy</answer>, <answer>energy</answer> can neither be created (produced) nor destroyed by itself. It can only be transformed. The total inflow of <answer>energy</answer> into a system must equal the total outflow of <answer>energy</answer> from the system, plus the change in the <answer>energy</answer> contained within the system. Energy is subject to a strict global conservation law; that is, whenever one measures (or calculates) the total <answer>energy</answer> of a system of particles whose interactions do not depend explicitly on time, it is found that the total <answer>energy</answer> of the system always remains constant.
What can neither be created nor destroyed by itself; it can only be transformed?
energy