Which statement best describes how energy changes in a simple machine?

• A. It disappears from the system.
• B. It changes into sound energy.
• C. It increases the total energy in the universe.
• D. It changes form between potential and kinetic energy but the total amount stays the same.

Answer: (D)

Energy in a simple machine is conserved and can move between stored energy and motion without creating or destroying it. As something moves through a simple machine, its energy can switch between potential energy (stored energy due to position) and kinetic energy (energy of motion). For example, an object at the top of a ramp has more potential energy, and as it slides down, that potential energy becomes kinetic energy while the total amount stays the same (ignoring friction). If friction or other losses are present, some energy still ends up as heat or sound, but the overall energy balance remains constant when all forms are counted.