When does potential energy become useful energy?

According to the Law of Conservation of Mass, energy is not created or destroyed and is equal to the sum of potential energy plus kinetic energy. 

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  Potential Energy: Potential energy is energy due to an object's position or condition. You can think of potential energy as energy that is stored and ready to be used. Types of potential energy: chemical energy, mechanical energy, nuclear energy, gravitational energy.

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  Kinetic Energy: Kinetic energy is energy due to motion. Types of kinetic energy: radiant energy, thermal energy, motion energy, sound energy, electrical energy

Potential energy becomes useful when it is converted to kinetic energy. Kinetic energy is used to perform work. Work occurs when force is applied to an object. Kinetic energy is useful because it allows work to be done.

Examples:

• Chemical energy (potential energy) is converted to thermal energy (kinetic energy) when gasoline is burned. The thermal energy is then used to make the car run (work).

• Gravitational energy from water stored behind a dam (potential energy) is converted to electrical energy (kinetic energy). Electrical energy is then used to power other processes (work).