Wikipedia's definition of energy can only be qualified as useless. Here is mine:
A bird that flies, a molecule in a gas possess energy since they move: this is kinetic energy.
A stone you hold still in your hand could move and therefore acquire kinetic energy if you let it fall: this is potential energy.
All forms of energy can transform into each other, their sum remaining always the same: this is the principle of conservation of energy.
Old NID
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