The energy that is not useful is called waste energy. It is the energy that is not harnessed or converted into a form that can be utilized for work or other useful purposes.
heat energy
Actually it is - very useful.
Currently, gold is not useful in any form of energy production.
A system that converts thermal energy into a form of useful mechanical or electrical energy is called a heat engine. This process involves using the temperature difference between a heat source and a heat sink to produce work, which can be used to generate electricity or perform mechanical tasks.
electricity
Usable energy is typically referred to as energy that can be easily converted and applied to perform work, such as electrical energy from batteries or kinetic energy from moving objects. It is energy in a form that can readily be harnessed to do useful work or produce heat.
Mechanical energy
Useful energy is the energy that is converted into a desired form of work or output, such as electricity or mechanical work. Wasted energy, on the other hand, is energy that is not converted into a useful form of work and is typically lost as heat or other forms of inefficiency.
A radio produces electromagnetic energy in the form of radio waves that are converted into sound waves by the radio's speaker, providing audible information and entertainment.
Useful energy is energy that is converted into a form that can directly perform work or be easily stored and retrieved for future use. It is typically in a form that can power machines, devices, or appliances efficiently, such as electricity or mechanical energy.
the thing that makes electricity such a useful form of energy is that electricity is renweable it comes from the skies "thunder" you can also generate electircity but still some things need electricity to help it generate. so......... electircity is a useful form of energy, but also wind, solar are also useful for of energy.