The law of conservation of energy states that energy can neither be created nor destroyed; it can only be transformed from one form to another or transferred between objects, so the total energy of an isolated system remains constant over time.

Core idea

  • In any isolated system, the total amount of energy stays the same, even though it may change form (for example, from chemical to heat to light).
  • This means energy is never “used up”; it is only converted or moved, such as electrical energy turning into light and heat in a bulb.

Simple examples

  • A falling object: Gravitational potential energy converts into kinetic energy as it falls, but the sum of potential plus kinetic energy stays constant (ignoring air resistance).
  • A swinging pendulum: Energy shifts back and forth between potential and kinetic, and gradually becomes thermal energy in the surroundings, yet the total energy of pendulum plus environment is unchanged.

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