Which statement best describes energy in a closed system during transformations?

Which statement best describes energy in a closed system during transformations?

• A. Energy can be created.
• B. Energy can be destroyed.
• C. Energy can be converted, but the total amount may not stay the same.
• D. The total energy remains constant; energy is conserved.

Answer: (D)

The main idea is energy conservation in a closed system: energy can shift between forms, but the total amount stays the same. In a closed system, energy can transform from kinetic to potential, chemical to thermal, and so on, yet the sum of all forms stays constant. For example, when friction converts some mechanical energy into heat, the mechanical energy decreases while heat increases, and the total energy remains constant. That’s why saying the total energy remains constant and energy is conserved is the best description. The other ideas aren’t accurate because energy isn’t created or destroyed in a closed system; it can be converted, but the total amount does not change.

The main idea is energy conservation in a closed system: energy can shift between forms, but the total amount stays the same. In a closed system, energy can transform from kinetic to potential, chemical to thermal, and so on, yet the sum of all forms stays constant. For example, when friction converts some mechanical energy into heat, the mechanical energy decreases while heat increases, and the total energy remains constant. That’s why saying the total energy remains constant and energy is conserved is the best description. The other ideas aren’t accurate because energy isn’t created or destroyed in a closed system; it can be converted, but the total amount does not change.