Energy is constant in an isolated system.The concept of energy was born long ago, in the ancient Greek philosophy, and later evolved into more tangible notions. Not only does the first law of thermodynamics describe the conservation of energy in a system: it also describes how energy transforms.

Energy conservation and transformation sparked the imagination of brilliant inventors, who built machines that help us do our work. This industrial revolution gifted us with countless inventions that are essential today, from refrigerators to rockets propulsion in outer space.