In this chapter we learn the principles that underlie the science of thermodynamics, which is a branch of physics and started dr investigation of various machines that are deliberately designed to do business. For example: car engines are designed to run cars, steam turbine electric generator rotor to rotate. Investigation of the activities of such tools which are all intended to be who called the effort was carried out by the system, since old habits born convention in thermodynamics gives positive marks on such efforts. If this resultant force in the direction of displacement, the product of force by the displacement is positive and
1. Work performed by the system
2. Energy reduced system, as long as no other energy transfer.
In the application of the convention marks the mechanics of the business in thermodynamics, need to be considered:
1. Calculate the force F which is done by the system
2. Calculate the displacement ds capture point F
3. If F and ds equal sign (unidirectional), positive effort
4. Bussiness positive, meaning done by the system
5. If a positive effort, the energy system is reduced, if no replacement dg energy in some way.
Suppose the cylinder cross-sectional area A and the pressure that is done by the system thd advance Pinton p. Then the force that carried out by the system is pA. If the piston moves outward as far as a very small distance dx, business dW this style are:
dW = pA dx while Adx = dV
where dV is the change in the system volume.
Heat transfer and work effort Provides two methods regarding the addition or subtraction of energy to the energy of a system. Once the energy transfer is completed, the system is said to have undergone a change of energy in the (inner life).
A system changes from state 1 to state 2 follow a certain path and then heat which is absorbed Q, and W measured effort. Q is the energy that is given to the system by heat transfer and W is the energy that is picked up from the system by the work effort. Then the difference between Q-W can be calculated. If now this case, we do well to various kinds of trails (from state 1 to 2) important outcome acquired is that the Q-W is the same for all of the tracks that connect 1 and 2. Therefore Q-W must describe the energy changes inner life of the system. Thus the inner life energy change sustu system does not depend on the trajectory, and therefore equal to the energy system in a state of reduced energy pad 2 state 1, or U2- U1:
U2 - U1 = Q - W
If the law is used in the form above, things that must be considered:
1. All quantities should be is expressed dlm same unit
2. Q positive when the heat goes into the system
3. W positive when the force and displacement systems do have the same direction.
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