# Principles of Flight

Classified in Physics

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1. TD principles

General principle: An isolated system always Attains equilibrium. The state changes only by varying external parameters. Bigger the system, longer the time to attain equilibrium.

Zeroth law of TD: If two systems are both in thermal equilibrium with a third System then they are in thermal equilibrium with each other.

The first principle of Thermodynamics: This Is the principle of the conservation of energy for macroscopic bodies. The increase in internal energy of a closed System is equal to the total of the energy added to the system. In particular, If the energy entering the system is supplied as heat and if energy leaves the System as work, the heat is accounted for as positive and the work as negative.   DU=δQ+δW

Second law: The first law states energy Balance, the second law deals with the direction of processes. In the relation Of the 1st law the only perfect (total) differential is dU. Elementary

Work δW and heat δQ Are not perfect total differentials. But it can be shown that using an Integrant factor, namely 1/T, we find a perfect diferential as below: δQ/T=dS. This is not a mathematical result, but a physical result from experiments Expressed in a

mathematical form. The new form of the 2nd Law is: elementary heat admits an integrating factor.