The English physicist James Joule studied the nature of heat, and established its relationship to mechanical work.
He showed that the various forms of energy mechanical, electrical, and heat are basically the same, and can be changed, one into another. This is known as the conservation of energy, and the idea was proved by Joule in a series of experiments.
In his early years, joule proved that heat produced in a small electromagnet built by him was from electrical energy, which was in turn, generated by mechanical energy which powered the dynamo. The principle of conservation of energy became the first law of thermodynamics, a field of physics that Joule is referred to as the chief founder of.
Joule was the first person to calculate the speed of a molecule of gas, about 457 meters a second for oxygen at average temperatures. This would lay the foundations for the kinetic theory of gases in the future. Joule recognized the need for standard units of electricity. In fact, the unit of energy is named the ‘joule’ in recognition of his contributions.