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Applied mechanics |Прикладная механика

Lesson 4

Read the text:  Machine

The scientific definition of a "machine" (derived from the latin machina) is any device that transmits or modifies energy. In common usage, the meaning is restricted to devices having rigid moving parts that perform or assist in performing some work. Machines normally require some energy source ("input") and always accomplish some sort of work ("output"). Devices with no rigid moving parts are commonly considered tools, or simply devices, not machines. People have used mechanisms to amplify their abilities since before written records were available. Generally these devices decrease the amount of force required to do a given amount of work, alter the direction of the force, or transform one form of motion or energy into another. The mechanical advantage of a simple machine is the ratio between the force it exerts on the load and the input force applied. This does not entirely describe the machine's performance, as force is required to overcome friction as well. The mechanical efficiency of a machine is the ratio of the actual mechanical advantage (AMA) to the ideal mechanical advantage (IMA). Functioning physical machines are always less than 100% efficient. Modern power tools, automated machine tools, and human-operated power machinery are tools that are also machines. Machines used to transform heat or other energy into mechanical energy are known as engines. Hydraulics devices may also be used to support industrial applications, although devices entirely lacking rigid moving parts are not commonly considered machines. Hydraulics are widely used in heavy equipment industries, automobile industries, marine industries, aeronautical industries, construction equipment industries, and earthmoving equipment industries. In physics, a simple machine is any device that only requires the application of a single force to work. Work is done when a force is applied and results in movement over a set distance. The work done is the product of the force and the distance. The amount of work required to achieve a set objective is constant; however the force required can be reduced provided the lesser force is applied over a longer distance. The ratio between the two forces is the mechanical advantage.

The traditional list of simple machines is:

·                The inclined plane

·                The wheel and axle

·                The lever

·                The pulley

·                The wedge

·                The screw

The ratio of the output force to the input force is the mechanical advantage. For example, the mechanical advantage of a lever is equal to the ratio of its two arms. The mechanical advantage of an inclined plane (with the force acting parallel to the plane) is the cosecant of the angle of inclination. These simple machines fall into two general classes; those dependent on the vector resolution of forces (inclined plane, wedge, screw) and those in which there is an equilibrium of torques (lever, pulley, wheel). Simple machines are often used in combination as components of more complex machines. For example: wheels, axles, levers, and pulleys are all used in the formation of modern bicycles.

Variations to the list of simple machines:

·       Some say there are only five simple machines, arguing that the wedge is a moving inclined plane.

·       Others further simplify the list to four saying that the screw is a helical inclined plane. This position is less accepted because a screw simultaneously converts a rotational force (torque) to a linear force.

 

1. Match the left part with the right:

1.  The ratio of the output force to the input force	a)  are often used in combination as components of more complex machines.
2.  Simple machines	b)  is the mechanical advantage.
3.  Hydraulic systems	c)   can also provide amplification of force but are not included in lists of simple machines.

 

2. Complete the sentences with the suggested words: equipment, heavy, simple, application

Hydraulics are widely used in _______ equipment industries, automobile industries, marine industries, aeronautical industries, construction _______ industries, and earthmoving equipment industries. In physics, a _______ machine is any device that only requires the _______ of a single force to work.