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MACHINES AND WORK

Defined in the simplest terms a machine is a device that uses force to accomplish something. More technically, it is a device that transmits and changes force or motion into work. This definition implies that a machine must have moving parts. A machine can be very simple, like a block and tackle to raise a heavy weight, or very complex, like a railroad locomotive or the mechanical systems used for industrial processes.

A machine receives input from an energy source and transforms it into output in the form of mechanical or electrical energy. Machines whose input is a natural source of energy are called prime movers. Natural sources of energy include wind, water, steam, and petroleum. Windmills and waterwheels are prime movers; so are the great turbines driven by water or steam that turn the generators that produce electricity; and so are internal combustion engines that use petroleum products as fuel. Electric motors are not prime movers, since an alternating current of electricity which supplies most electrical energy does not exist in nature.

The terms like work, force, and power are frequently used in mechanical engineering, so it is necessary to define them precisely. Force is an effort that results in motion or physical change. If you use your muscles to lift a box you are exerting force on that box. The water which strikes the blades of a turbine is an exerting force on those blades, thereby setting them in motion.

In a technical sense work is the combination of the force and the distance through which it is exerted.

To produce work, a force must act through a distance. If you stand and hold a twenty-pound weight for any length of time, you may get very tired, but you are not doing work in an engineering sense because the force you exerted to hold up the weight was not acting through a distance. However, if you raised the weight, you would be doing work.

Power is another term used in a special technical sense when speaking of machines. It is the rate at which work is performed.

In the English-speaking countries, the rate of doing work is usually given in terms of horsepower, often abbreviated hp. You will remember that this expression resulted from the desire of the inventor James Watt to describe the work his steam engines performed in terms that his customers could easily understand. After much experimentation, he settled on a rate of 33,000 footpounds per minute as one horsepower.

In the metric system power is measured in terms of watts and kilowatts. The kilowatt, a more widely used term, equals a thousand watts or approximately 1/3 horsepower in the English system.

Упражнение 3. Соедините термин с соответствующим ему определением, данным в правой колонке.

Упражнение 4. Прочитайте внимательно два последних абзаца и заполните сле-дующую таблицу, в которой должно быть показано соотношение между единицами мощности в разных системах.

Упражнение 5. Распределите следующие слова в три группы: а) обозначающие основные понятия физики и механики; б) обозначающие источники энергии; в) меха-низмы, машины:

wind, power, water, force, work, steam, wind mill, petroleum, turbine, motion, weight, block, device, locomotive, input, output, steam engine, rate, effort, distance, generator, part, weight.

Упражнение 6. Следующие глаголы часто сочетаются с понятиями физики и механики. Составьте с ними глагольные сочетания, используя материал текста.

Model: to transmit − to transmit motion / force

to produce, to transform, to supply, to result in, to exert, to set, to perform, to result from, to measure... in.

Упражнение 7. Изучите внимательно второй абзац текста еще раз и сгруппируйте следующие существительные в таблицу:

wind mill, wind wheel, steam engine, electric motor, internal combustion engine, turbine.

Упражнение 8. Подготовьте развернутые ответы на следующие вопросы:

1. What is a simple definition of a machine? What is a more technical definition? What does this definition imply? 2. Describe some very simple machines. What are some complex ones?
3. What are the machines called whose input is a natural source of energy? What are some natural sources of energy and the machines that use them? 4. Why aren't electric motors prime-movers? 5. What is force? Give some examples. 6. What is work? How can work be expressed mathematically? Give an example. 7. What is power? 8. How is the rate of doing work usually given in the English-speaking countries? Why was the term invented? 9. In what terms is power measured in the metric system?

TEXT 3

Упражнение 1. Прочтите и дайте перевод интернациональных слов и выражений с учетом указанной части речи:

Упражнение 2. Прочтите опорные словосочетания и предложения и подберите к ним соответствующий перевод:

Упражнение 3. Прочтите текст и выберите из него наиболее часто повторяющиеся слова, которые можно рассматривать как ключевые.

Слова к тексту:

1. There are three types of internal combustion engines, which are of great importance to our industrial life and us. These three are the petrol engine, the diesel engine and the gas turbine.

2. They all three breathe air. They burn a liquid hydrocarbon fuel. They produce mechanical work and also, a great disadvantage, exhaust gases.

3. However, there are differences in the principles of their construction and operation. The first two, the petrol engine and the diesel engine are reciprocating engines. That is, they are based on a piston moving within a cylinder. The third engine, the one we are most interested in today, the gas turbine, is a rotary engine.

4. There are two basic types of a rotary engine, the turbo-jet and the turbo-prop. The turbo-jet is a very reliable engine. It consists of a main shaft at one end of which there is an axial compressor and the other end is a turbine. The purpose of this turbine is to drive the compressor. Between the compressor and the turbine are combustion chambers into which the fuel is injected. The fuel is, in fact, kerosene.

5. Air enters the compressor, the compressor is turning. As it passes through the compressor it increases both in pressure and in temperature. Then it flows into the combustion chambers, mixes with the fuel and at constant pressure the temperature goes up to a very high level. The gases then expand through the turbine. The turbine extracts work from those gases and turns the compressor. So, the turbine has no part in propelling the aircraft to which this turbine is attached. The propulsion of the aircraft is due to the reaction of the exhaust gases. A jet engine is a reaction engine.

6. The second type is the turbo-prop. The two engines are fundamentally the same: a turbine, a compressor and combustion chambers between the two of them. But here instead of an axial compressor, we have a centrifugal compressor. In this engine, the turbine has two functions. It not only has to run the compressor, it also turns the propeller because it is a propeller engine.

7. Both of these engines have certain advantages over a reciprocating engine. The first and the most important is that these engines have a high power-weight ratio. In other words, for a given weight of engine the power they produce is much larger than that of a piston engine. The second characteristic is that they are very simple and have a very small number of moving parts. The third one is that they are able to run independent of water supply. Of great importance is their rapid starting. From the time you start the run-up procedure to the time the full power is developed is about 30 seconds compared to some minutes with a reciprocating engine.

8. The major use of these engines is in aviation. Because of the high power-weight ratio, it has made aviation faster. There are other uses, one of them being in electricity generation.

Упражнение 4. Прочтите предложения.

1. They produce mechanical work and..., a great disadvantage, exhaust gases.

2...., the turbine has no part in propelling the aircraft to which this engine is attached.

3. …, for a given weight of engine the power they produce is much larger than that of a piston engine.

4.... there are differences in the principles of their construction and operation.

Выберите и вставьте пропущенные в них следующие слова-связки:

Переведите предложения.

Упражнение 5. В абзаце, начинающемся со слов «Both of these engines...», найдите слова с суффиксом «-ing». Поясните, к какой части речи они относятся, переведите эти слова по контексту.

Упражнение 6. Ответьте на вопросы.

1. How many types of internal combustion engines are there?

2. The engines are based on a bar moving within a cylinder, aren't they?

3. Does the air in the compressor increase both in pressure and in temperature?

4. Which of these engines have certain advantages over a reciprocating ones?

5. Where are the combustion chambers set in the rotary engine?

6. Is the gas turbine of a diesel engine type or a rotary one?

Упражнение 7. Укажите номер абзаца, в котором излагаются принципиальные конструкционные и рабочие отличия бензинового и дизельного двигателей от газового двигателя.

Упражнение 8. Закончите предложение таким образом, чтобы его можно было использовать в качестве обобщающего сообщения:

The text tells us...

a)... about the origin of the engines.

b)... these three types of internal combustion engines breathe air, burn liquid hydrocarbon fuel and produce mechanical work.

c)... the available internal combustion engines are harmful for the environment.

Упражнение 9. Предложите свои варианты заглавия текста.

Упражнение 10. Скажите, какую информацию из текста вы узнали впервые.

Упражнение 11. Скажите, при изучении каких предметов вам может понадобиться информация, содержащаяся в данном тексте.

Упражнение 12. Обобщите информацию в виде резюме, используя ключевые слова, фразы-клише.

TEXT 4

Упражнение 1. Догадайтесь о значении интернациональных слов:

Упражнение 2. Подберите соответствующие русские эквиваленты:

Упражнение 3. Сравните однокоренные слова, выделите в них общую основу и определите, к какой части речи они относятся:

friction, frictional, frictionless; formation, transformation, transforming; reversible, irreversible, reverse; reduce, reduction; gradation, degradation; available, availability.

Упражнение 4. Выберите из приведенных предложений те, которые содержат страдательный залог. Объясните, по каким признакам вы установили грамматическую форму.

1. The production of heat^: by mechanical means may be illustrated by the phenomenon of friction.

2. In the case of the ideal reversible process, there is no change in the quantity of available energy.

3. A strictly reversible frictionless process being an ideal, it may be approached but never attained.

4. The total energy of an isolated system remains constant and cannot be increased or diminished by any physical process.

5. When heat is employed to do work, a quantity of heat precisely equivalent to the work done disappears.

6. No change in a system of bodies that takes place of itself can increase the available energy of the system.

Упражнение 5. Прочтите текст. Найдите в нем предложения, выражающие основные положения текста.

Слова к тексту: