Law of conservation of energy does not distinguish between useful and wasted energy. The law neglects ‘losses’ from the closed system into the environment.
In an energy conservation process, energy is transmitted from one or more forms to another form forms resulting in certain work, heat transfer and energy loss.
In a closed system containing certain quantity of matter and energy, several energy transformations may take place from one form to another. The total mass and energy in the closed system remains unchanged.
Some of the examples of energy transformations:
- Turning on a car’s engine transforms the chemical energy in gasoline into the mechanical energy that powers the engine, with heat energy released as a by-product.
- Trees and plants transform radiant energy from sunlight into the chemical energy in simple sugars through the process of photosynthesis.
- A thermonuclear reaction changes nuclear energy to radiant energy and heat energy.
- An electric mixer changes electrical energy to mechanical energy and heat energy.
- Driving a nail into wood with hammer changes mechanical energy to deformation and heat energy.
- An electric desk lamp changes electrical energy to radiant energy and heat energy.
Image source: Britannica: Kids Encyclopedia