Page 10 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

1.0 FUNDAMENTAL CONCEPTS OF THERMODYNAMICS

Did you realize that the work of an engineer is limited unless he has a source of power to

drive his machines or tools? However, before such a study can begin, it is necessary to be

sure of the number of definitions and units, which are essential for a proper

understanding of the subject. We are familiar with most of these items in our everyday
lives, but science demands that we have to be exact in our understanding if real progress

is to be made.

When engineering calculations are performed, it is necessary to be concerned with the
units of the physical quantities involved. A unit is any specified amount of a quantity by

comparison with which any other quantity of the same kind is measured. For example,

meters, centimeters and millimeters are all units of length. Seconds, minutes and hours

are alternative time units.

1.1 Fundamental and Derived Quantities

In the present discussion, we consider the system of units called SI (International System

of Units) and it is a legally accepted system in many countries.
Length, mass, time, electric current, thermodynamic temperature and luminous intensity

are the six fundamental physical quantities. These six quantities are absolutely

independent of one another. They are also called the ‘Indefinables’ of mechanics. The SI

base units are listed in Table 1.1-1.

Table 1.1-1 Fundamental units

Quantity Unit Symbol

Mass kilogram kg
Time second s
Length meter m
Thermodynamic temperature degree Kelvin K
Electric current ampere A
Luminous intensity candela cd

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