Simply speaking, “A machine is a device which received energy in some available form and utilizes it to do some particular type of work” or “A machine may be regarded as an agent for transmitting or modifying energy”.
A machine is a combination of components which can transmit power in a controlled manner and which is capable of performing useful work. A machine consists of a number of kinematically related links.A machine is a combination of resistant bodies (links or elements) with successfully constrained relative motions, which is used for transmitting other forms of energy into mechanical energy or transmitting and modifying available energy to do some particular kind of work.
Every machine will be found to consist of a system of parts (links or elements) connected together in such a manner that, if one be made to move, they all receive a motion, the relation of which to that of the first depends upon the nature of connections (i.e. joints).
The links may be rigid, rigid-hydraulic, or rigid-pneumatic. The power input may be mechanical, electrical, hydraulic, chemical, or nuclear. The power output may be mechanical, electrical hydraulic or thermal.
Examples of machines:
Heat engine- Receives heat energy and transformers it into mechanical energy.
Electric motor- Changes electric energy into mechanical energy.
A pump- Input electric power and output hydraulic power.
The majority of machines receives mechanical energy, and modify it so that the energy can be used for doing some specific task, for which it is designed, common examples of such machines being hoist, lathe, screw jack, etc.
Note:-It should be noted that machine must be capable of doing useful work. A series of kinematically related links put into motion with no output link, and which simply converts input energy to friction heat, is not a machine, unless the original purpose was only to generate heat.
CLASSIFICATION OF MACHINES
1. Machines for generating mechanical energy
- Converts other forms of energy into mechanical work
Examples: Steam engines, Steam turbines, I. C. engines, gas turbines, water turbines etc
2. Machines for transmitting mechanical energy into other form of energy
- Known as converting machines
Examples: Electric generators, air or hydraulic pumps, etc.
3. Machines for utilizing mechanical energy in the performance of useful work.
Examples: Lathe, and other machine tools, etc.
The transmission and modification of energy within the machine require the inclusion of a number of parts (links or elements), which are so selected that they will produce the desired motion and carry with safety the forces to which they are subjected so that the machine can perform its task successfully.
The study of relative motion between the various parts of a machine, and the forces which act on them, is covered under they field of “Theory of machines”, or “The Theory of Machines may be defined as that branch of engineering science which deals with the study of relative motion between various elements of a machine and the forces which act on them.
DIFFERENCE BETWEEN MACHINE AND MECHANISM
In kinematics, a mechanism is a mean of transmitting, controlling, or constraining relative movement. The central theme for mechanisms is rigid bodies connected together by joints. It can also be defined as a combination of resistant bodies that are shaped and connected in such a way that they move with definite relative motion with respect to each other.
A machine is a combination of rigid or resistant bodies, formed and connected in such a way th