Heat transfer, and the first law of thermodynamics
physics.bu.edu › ~duffy › py105The first law of thermodynamics relates changes in internal energy to heat added to a system and the work done by a system. The first law is simply a conservation of energy equation: The internal energy has the symbol U. Q is positive if heat is added to the system, and negative if heat is removed; W is positive if work is done by the system, and negative if work is done on the system.
Heat equation - Wikipedia
https://en.wikipedia.org/wiki/Heat_equationInformally, the Laplacian operator ∆ gives the difference between the average value of a function in the neighborhood of a point, and its value at that point. Thus, if u is the temperature, ∆ tells whether (and by how much) the material surrounding each point is hotter or colder, on the average, than the material at that point. By the second law of thermodynamics, heat will flow from hotter bodies to adjacent colder bodie…