1)Read and translate the text. Mechanism: the fundamental physical or chemical processesinvolved in or responsible for an action, reaction or other natural phenomenon.
Machine: an assemblage of parts that transmit forces, motion and energy in a predetermined manner.
Simple Machine: any of various elementary mechanisms having the elements of which all machines are composed. Included in this category are the lever, wheel and axle, pulley, inclined plane, wedge and the screw.
The word mechanism has many meanings. In kinematics, a mechanism is a means of transmitting, controlling, or constraining relative movement. Movements which are electrically, magnetically, pneumatically operated are excluded from the concept of mechanism. The central theme for mechanisms is rigid bodies connected together by joints.
A machine is a combination of rigid or resistant bodies, formed and connected so that they move with definite relative motions and transmit force from the source of power to the resistance to be overcome. A machine has two functions: transmitting definite relative motion and transmitting force. These functions require strength and rigidity to transmit the forces.
The term mechanism is applied to the combination of geometrical bodies which constitute a machine or part of a machine. A mechanism may therefore be defined as a combination of rigid or resistant bodies, formed and connected so that they move with definite relative motions with respect to one another.
Although a truly rigid body does not exist, many engineering components are rigid because their deformations and distortions are negligible in comparison with their relative movements.
The similarity between machines and mechanisms is that
• they are both combinations of rigid bodies
• the relative motion among the rigid bodies are definite.
2)Give the short summary to the text.

The difference between machine and mechanism is that machines transform energy to do work, while mechanisms so not necessarily perform this function. The term machinery generally means machines and mechanisms. Figure 1 shows a picture of the main part of a diesel engine. The mechanism of its cylinder-link-crank parts is a slider-crank mechanism, as shown in Figure 2.

Figure 2-2 Skeleton outline Figure 2-1 Cross section of a power cylinder in a diesel engine
Types of Machines
By means of a machine an applied force is increased, its direction is changed, or one form of motion or energy is changed into another form. Thus defined, such simple devices as the lever, the pulley, the inclined plane, the screw, and the wheel and axle are machines. They are called simple machines; more complicated machines are merely combinations of them. Of the five, the lever, the pulley, and the inclined plane are primary; the wheel and axle and the screw are secondary. The wheel and axle combination is a rotary lever, while the screw may be considered an inclined plane wound around a core. The wedge is a double inclined plane.
Complex machines are designated, as a rule, by the operations they perform; the complicated devices used for sawing, planing, and turning, for example, are known as sawing machines, planing machines, and turning machines respectively and as machine tools collectively. Machines used to transform other forms of energy (as heat) into mechanical energy are known as engines, i.e. the steam engine or the internal-combustion engine. The electric motor transforms electrical energy into mechanical energy. Its operation is the reverse of that of the electric generator, which transforms the energy of falling water or steam into electrical energy.

3)Name the main types of machines.

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