Who measured the mechanical equivalent of heat energy related to temperature changes?

The measurement of the mechanical equivalent of heat energy is largely credited to James Prescott Joule. He conducted experiments that demonstrated the relationship between mechanical work and heat, ultimately leading to the conclusion that heat can be quantified in terms of mechanical energy. Joule's work involved using a falling weight to turn a paddle in a water tank, generating heat through friction, which allowed him to calculate the amount of heat produced in terms of the work done by the weight. This foundational work helped establish the first law of thermodynamics and laid the groundwork for the field of energy conversion.

In contrast, Daniel Bernoulli contributed to fluid dynamics and kinetic theory, Albert Einstein is known for his theories of relativity and contributions to modern physics, and Isaac Newton's work focused primarily on classical mechanics and gravitation, without direct involvement in the quantification of heat energy. Thus, Joule's specific focus on mechanical energy and heat definitively establishes him as the key figure in this context.