Benjamin Thompson carried out a series of experiments that related mechanical work and heat. Later James Joule resumed Benjamin Thompson's experiments.
The first law of thermodynamics was announced by Julius Robert von Mayer in 1841. Mayer was the first to verify the transformation of mechanical work into heat, and vice versa.
These checks were done at the same time as Joule but separately. Both in the 19th century.
The first complete declarations of the law came in 1850 from Rudolf Clausius and William Rankine. Rankine's statement is considered less different from Clausius'.
The first law of thermodynamics states that: "The total energy of an isolated system is neither created nor destroyed, it remains constant".
Nicolas Léonard Sadi Carnot, the considered father of thermodynamics
Paris, June 1, 1796 - August 24, 1832
Nicolas Léonard Sadi Carnot was a pioneering French physicist and engineer in the study of thermodynamics. He is recognized today as the founder or father of thermodynamics.
When Carnot began to work on this matter, steam engines had achieved great economic and industrial importance. However, there had been no actual scientific study of them.
Carnot wanted to answer two questions about the operation of heat engines. Both related to its thermal performance.
Like Copernicus, Carnot only published one book: "Reflections on the Motive Power of Fire" (Paris, 1824). In his book he expressed the first successful theory of maximum efficiency of heat machines.
In this work he laid the foundations for a completely new discipline in physics: thermodynamics.
Carnot cycle
The Carnot cycle is the most efficient motor possible. This efficiency is not solely due to the absence of friction and other incidental waste processes. The main reason is that it does not involve heat conduction between the engine parts at different temperatures.
Carnot knew that the conduction of heat between bodies at different temperatures is a wasteful and irreversible process. Heat conduction must be removed for the heat engine to achieve maximum efficiency.
James Prescott Joule. Heat and energy
Salford, December 24, 1818 - Sale, October 11, 1889.
Joule studied the characteristics of heat and discovered the relationship with energy. This led to the law of conservation of energy (first law of thermodynamics).
The SI power unit, July, is named after him.
He developed the absolute temperature scale with Lord Kelvin, described magnetostriction, and found the relationship between electric current through an electrical resistance and heat dissipation, known as Joule's law.
Thanks to his experiments, he showed that heat and mechanical work could convert each other directly, keeping their general value constant: in hydraulic and mechanical machines, friction transforms mechanical power into heat.
On the contrary, in thermal machines, the mechanical effect produced (work) derives from an equivalent amount of heat.
Joule began to lay the experimental foundation for the first law of thermodynamics.
Initially, Joule and Julius Robert von Mayer, who had come up with similar findings, were ignored until the German physicist Hermann Helmholtz discovered their findings in 1842. He gave them due recognition when he published his final Energy Conservation Act in 1847.
James Prescott Joule Mechanical Experiment
James Joule proposed a device consisting of a rotary shaft fitted with a series of blades rotating between four sets of stationary blades. The purpose of these paddles was to stir the liquid placed in the free space between them. The shaft was connected by a system of very fine pulleys and ropes to a pair of masses of known weight.
The walls of the container were watertight and made of very thick wood to simulate an adiabatic wall.
The experiment consisted of:
Wind the rope holding the masses on the pulleys until they are placed at a certain height from the ground.
Drop the masses.
The axis begins to rotate, generating a rotation of the revolving arms, stirring the liquid, giving up part of its kinetic and potential energy.
This process was repeated twenty times. At the end, the temperature of the liquid was measured.
First results
After careful repetition, Joule concluded that the amount of heat produced by friction between bodies, whether liquid or solid, is always proportional to the amount of mechanical work supplied.
Later he carried out more experiments varying:
The type of mechanical work.
The type of liquid and, therefore, its properties.
The results of all experiments showed that the change observed in the system is always the same. In this experiment the change is registered by the variation of the system temperature. Always in systems isolated from the outside.
It is important to note that in these experiments they complete the following characteristics:
The system does not move.
Its kinetic energy is zero.
It does not move with respect to the ground level.
Its potential energy remains constant
The system has absorbed a certain amount of energy.
What is internal energy?
Joule's experiments concluded that the heat transfer in a thermal machine became part of the internal energy of the machine.
If we supply any closed system with a certain amount of mechanical energy W, it only causes an increase in the internal energy of the thermodynamic system.
The internal energy variation in an adiabatic process is equal to the supplied work.
An adiabatic process is a process that does not exchange heat with the outside. If the system is not adiabatic, the internal energy is equal to the work minus the thermal energy that has gone out.
Julius Robert von Mayer, the first in history to formulate the first law of thermodynamics
Heilbronn, November 25, 1814 - March 20, 1878.
Julius Robert von Mayer was a German physician and physicist and one of the founders of the principles of thermodynamics.
Julius Robert von Mayer was largely ignored by other professionals in the area. So Mayer became interested in the area of heat and its movement. It presented a value in numerical terms for the mechanical equivalent of heat.
In 1841 he was the first to formulate the principle of conservation of energy. By extension, he also formulated the first law of thermodynamics.
Since he was not taken seriously at the time, his accomplishments were overlooked and James Joule was credited.
On the priority of this discovery, he had a great disagreement with the English physicist James Prescott Joule.