2026-09-04 12:31:07: Physics 2

physics/Thermodynamics/Entropy and Second Law of Thermodynamics.md

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+[[Thermodynamics]]
+# Summary
+* Entropy describes energy's tendency to spread out and cause some of the energy to become useless.
+* Entropy decreases when energy is organized, increases when spread out.
+* Higher entropy means more useless energy.
+* Total entropy of an isolated system never decreases over time.
+* Entropy remains constant only in perfectly reversible processes (theoretical).
+* IRL, entropy always increases.

physics/Thermodynamics/First Law of Thermodynamics.md

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+[[Thermodynamics]]
+# Summary
+* First law: $\Delta U=Q+W$
+* Q is heat added W is work done
+* Internal energy $U$ is the sum of kinetic energy and potential energy. Ideal gas has no internal potential energy, so solely kinetic.
+* Ideal monatomic gas has formula: $U=\frac{3}{2}Nk_BT=\frac{3}{2}nRT$ 
+* Work done on gas by external pressure: $W=-P\Delta V$
+* Negative sign means expansion does negative work on gas.
+* On a PV graph, integrals are work done, and straight lines are isotherms.
+* Four special processes:
+	* Isovolumeric $W = 0$
+	* Isothermic $\Delta U = 0$ For an ideal gas
+	* Isobaric $W=-P\Delta V$
+	* Adiabatic $Q=0$

physics/Thermodynamics/Thermodynamics.md

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-[[Physics]]
+[[physics]]