#### Henri Poincaré: On the Partial Differential Equations of Mathematical Physics – Law of cooling of an isolated solid body in space

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Suppose we are looking for the law of cooling of an isolated solid body in space. It will be a question of finding a function V satisfying the equation dV/dt = kΔV, and which moreover is given for t = … Read More

#### Thermal transfer

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A thermal transfer, more commonly called heat, is, along with work, one of the modes of internal energy exchange between two systems: it is a transfer of thermal energy that takes place outside thermodynamic equilibrium. There are three types of … Read More

#### Henri Poincaré, Quanta hypothesis: More on quanta of energy

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Statistical equilibrium can only be established if there is exchange of energy between the resonators, otherwise each resonator would retain its initial energy, which is arbitrary, indefinitely, and the final distribution would obey no law. This exchange could not be … Read More

#### Henri Poincaré, Quanta hypothesis: The law of radiation

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Physicists did not at first concern themselves with these difficulties, but two new facts changed the face of things; the first is what is called the law of black radiation. A perfectly black body is one whose absorption coefficient is … Read More

#### Henri Poincaré, Quanta hypothesis: Thermodynamics and probability

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Let us go back to the kinetic theory of gases; the gases are formed of molecules which circulate in all directions with great velocities; their trajectories would be rectilinear if from time to time they did not collide each other, … Read More

#### Temperature, Heat, Expansion

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(The Sun, the main source of heat on Earth.) Temperature Temperature is a physical quantity measured using a thermometer and studied in thermometry. In everyday life, it is connected to the sensations of cold and heat, coming from the heat … Read More

#### Heat

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A thermal transfer, more commonly called heat, is one of the modes of heat energy exchange between two systems. This is a fundamental notion of thermodynamics. Unlike work, heat is a disorderly microscopic energy transfer. There are three types of … Read More