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 form 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.

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. The water which strikes the blades of a turbine is 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 in speaking of machines. It is the rate at which work is performed. The rate of doing work is sometimes given in terms of horsepower, often abbreviated hp. 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 foot-pounds 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 1/3 horsepower in the English system.

2. Translate the sentences in written form.

1. If a device transmits force into motion it is called a machine. 2. If a device transmitted force into motion it would be called a machine. 3. If you stood and held weight, you would not be doing work. 4. If you raised the weight, you would be doing work. 5. If we were pulling a rubber band and then stopped pulling it, the rubber band would quickly return to its original shape and size. 6. If defective castings were brought in for analysis of their defects yesterday, they were tested.7. If defective castings were brought in for analysis, they would be tested. 8. If we expanded a spiral of lead wire a little, it would assume its original shape again afterwards. 9. If there had been no electrical connection between the zinc and the copper but little zinc would have dissolved.

3. State the type of the conditional sentences. Translate them into Ukrainian.

1. If the new equipment had been delivered in time yesterday, there would have been no problem at all. 2. If the conditions were unchanged, the automobile would travel 60 km per hour. 3. If the pulley had been frictionless the effort E would have been exactly equal to the load W. 4.If highly durable metal alloys had not been developed, there would be no modern rockets and aviation today. 5. If we could obtain ultrahigh-strength and super-refractory materials having close-packed structures the efficiency of all heat engines would approach 100 percent, as it would be possible for designers to use higher temperatures that today seem unthinkable; the motors could be made far lighter and more compact, since not only their efficiency, but also their specific output would be raised by several times.

4. Put the verbs in brackets in the required forms and translate the sentences into Ukrainian.

1.If they (use) another method, the results would have been different. 2. If the complete list of details had been prepared the engineer (buy) everything in time. 3. If the load (increase) the speed would decrease. 4. If all the people of the world (count) the atoms in a drop of water they would not be able to finish their work even in ten thousand years. 5. If one knows the dimensions of the body he (calculate) easily its volume. 6.If every star in the sky were to shine with the same degree of brightness, the distance to any star (can) readily be established. 7. If he (know) the specific heat and the weight of the substance, he would have calculated its thermal capacity. 8. If you rubbed the stick, it (become) warm.