The laws of thermodynamics explain the effects of heat in an engine. The first law states that energy can be changed but it cannot be destroyed. In a gas turbine engine, heat energy is changed to mechanical energy. The second law of thermodynamics states that heat cannot be transferred from a cooler body to a hotter body. In a gas turbine engine, heat is transferred from the hotter engine to the cooler lube oil.
Newton's first law explains why a force is needed to make the gas turbine work. In the figure, a ball on a level table will not move until it is made to move by some force such as the wind or pushing it by hand. Similarly, until the fuel and air mixture is burned in the gas turbine, there is no force for the turbine to use to turn the rotor shaft.
Newton's Second Law explains why the air must be compressed and accelerated to create a force. In the figure, a hammer is used to drive a nail. The force of hitting the nail is proportional to the mass (weight) of the hammer multiplied by the velocity of the hammer when it hits the nail. If you also use a heavier hammer, it is even easier to drive the nail into the wood. Mass and acceleration directly affect the amount of force created. The more compressed air (mass) that enters the gas turbine, the more force created from the combustion process.
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