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# Conversion and conservation of energy

The law of conservation of energy says that energy cannot be created or destroyed.

Energy can only be converted from one form to another or transferred between different systems.

The gravitational potential energy of an object on a cliff gets converted into kinetic energy if it is pushed over the edge.

If we ignore air resistance then: $$\begin{gather*} \\ \Tblue{\text {mass} \times \text{height} \times \text{gravitational field strength}} \\=\\ \Tred{\frac{1}{2} \times \text{mass} \times \text{speed}^{2}} \end{gather*}$$

The chemical potential energy inside coal is converted into thermal energy when the coal is burnt. This thermal energy can then be turned into electrical energy in a power plant.

Wind turbines convert the kinetic energy of the air into electrical energy.