Which statement best describes the law of conservation of energy?

Which statement best describes the law of conservation of energy?

• A. Energy is not conserved over time.
• B. Energy is conserved over time.
• C. Energy is created and destroyed.
• D. Energy is produced by machines.

Answer: (B)

Energy cannot be created or destroyed; it can only change from one form to another, and in a closed system the total amount stays the same over time. This is why the statement that energy is conserved over time is the best description. For example, a swinging pendulum continuously trades potential energy for kinetic energy as it moves; if you ignore friction, the total energy remains constant. In real life, some energy becomes heat due to friction, but the overall energy, including that heat, is still conserved. Machines don’t create energy—they transform it from one form (like chemical or electrical energy) into others (motion, light, sound), with some energy losses accounted for as heat. The other statements—energy not being conserved, energy being created or destroyed, or energy being produced by machines—conflict with this principle.

Energy cannot be created or destroyed; it can only change from one form to another, and in a closed system the total amount stays the same over time. This is why the statement that energy is conserved over time is the best description. For example, a swinging pendulum continuously trades potential energy for kinetic energy as it moves; if you ignore friction, the total energy remains constant. In real life, some energy becomes heat due to friction, but the overall energy, including that heat, is still conserved. Machines don’t create energy—they transform it from one form (like chemical or electrical energy) into others (motion, light, sound), with some energy losses accounted for as heat. The other statements—energy not being conserved, energy being created or destroyed, or energy being produced by machines—conflict with this principle.