Theory of Machines - Khurmi and Gupta
Introduction
1.1. Definition
The subject Theory of Machines may be defined as that branch of Engineering-science, which deals with the study of relative motion between the various parts of a machine, and forces which act on them. The knowledge of this subject is very essential for an engineer in designing the various parts of a machine.
Note: A machine is a device which receives energy in some available form and utilises it to do some particular type of work.
1.2. Sub-divisions of Theory of Machines
The Theory of Machines may be sub-divided into the following four branches :
1. Kinematics. It is that branch of Theory of Machines which deals with the relative motion between the various parts of the machines.
2. Dynamics. It is that branch of Theory of Machines which deals with the forces and their effects, while acting upon the machine parts in motion.
3. Kinetics. It is that branch of Theory of Machines which deals with the inertia forces which arise from the combined effect of the mass and motion of the machine parts.
4. Statics. It is that branch of Theory of Machines which deals with the forces and their effects while the machine parts are at rest. The mass of the parts is assumed to be negligible.
1.3.Fundamental Units
The measurement of physical quantities is one of the most important operations in engineering. Every quantity is measured in terms of some arbitrary, but internationally accepted units, called fundamental units. All physical quantities, met within this subject, are expressed in terms of the following three fundamental quantities :
- Length (L or l ),
- Mass (M or m), and
- Time (t).
1.4. Derived Units
Some units are expressed in terms of fundamental units known as derived units, e.g., the units of area, velocity, acceleration, pressure, etc.
1.5. Systems of Units
There are only four systems of units, which are commonly used and universally recognised. These are known as :
- C.G.S. units,
- F.P.S. units,
- M.K.S. units, and
- S.I. units.
1.6. C.G.S. Units
In this system, the fundamental units of length, mass and time are centimetre, gram and second respectively. The C.G.S. units are known as absolute units or physicist's units.
1.7. F.P.S. Units
In this system, the fundamental units of length, mass and time are foot, pound and second respectively.
Baca Juga :
1.8. M.K.S. Units
In this system, the fundamental units of length, mass and time are metre, kilogram and second respectively. The M.K.S. units are known as gravitational units or engineer's units.
1.9.Inter na tional System of Units (S.I Units)
The 11th general conference* of weights and measures have recommended a unified and systematically constituted system of fundamental and derived units for international use. This system is now being used in many countries. In India, the standards of Weights and Measures Act, 1956 (vide which we switched over to M.K.S. units) has been revised to recognise all the S.I. units in industry and commerce.
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