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Read the text and write sentences that give the definition of force, work, power and energy.

Force, Work, Power and Energy

Force is a "push", or a "pull"; it tends to produce, change, or check motion. Gravitation is the attraction between masses. The force of attraction between two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres. The dyne and the newton are the metric units of force. The pound is the unit of force in the English system.

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If you hold a bag of cement weighing 94 lb. on your shoulder­ all day long, you are merely exerting a force. In the scientific sense you are not doing any work. You do work when you put the bag of cement on your shoulder, or carry it up a flight of stairs. When a force acts upon a body and produces motion, work is done upon that body. In measuring work we consider two factors: force and distance. The amount of work clone is equal to the product of force times distance.¹ The erg and the joule are the metric units of work. Sometimes the gramme-centimetre and the kilogramme-metre are also used, with the understanding that it is a gram­me-weight, or kilogramme-weight of force that is employed. The foot-pound is the English unit of work.

Power is the rate of doing work. Power depends upon three factors: the force exerted, the distance the force moves, and the time required. In a scries of experiments, James Watt, the inventor of the steam engine, found that an Eng­lish dray horse could continue for a reasonable length of time to work at the rate of 550 ft. lb. per sec. In the English system, the horse-power is the unit of power; it is equal to 550 ft. 1b. per second. The horsepower, watt, and kilo­watt are the units of power. The watt is equal to one joule per sec. The kilowatt equals 1000 watts, The horsepower is equal to 746 watts.

Energy is the capacity for doing work. The units of work are used to measure energy. Energy may be transformed in practically any manner. While the quantity of energy remains constant in ordinary transformations, matter and energy are interchangeable on an atomic scale.

In dealing with force, we consider magnitude only; with work, we consider both magnitude and distance; with power, we consider magnitude, distance, and time.

N о t e

¹-the product of force times distance -— произведению силы нa расстояние

Now read the text again and note the important details.

1. Guess the meaning of these words:

produce, attraction, directly proportional, inversely proportional, product, centre, dyne, erg, newton, cement, act, joule, series, kilowatt, transformed, manner.

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2. Translate these sentences in a written forth: .

1. If you hold a bag of cement weighing 94 lb. on your shoulder all day long, you are merely exerting a force. 2.You do work when you put the bag of cement on your shoulder, or carry it up a flight of stairs. 3. In a series of experiments James Watt, the inventor of the steam engine, found that an English dray horse could continue for a reasonable length of time to work at the rate of 550 ft. lb. pet .sec.

3. Build a plan and speak about the main content of the text.

UNIT 7

TEXT. THE CONSERVATION AND TRANSFORMATION OF ENERGY

Einstein's work on the theory of relativity which he put forward early in the present century has altered our ideas regarding mass and energy as being separate and distinct from one another.¹ Einstein has simplified our picture of the universe by showing that the mass and energy can be converted from one to the other. This view has been supported by a number of experiments. Until this theory was put forward two fundamental laws were accepted by physicists.

Firstly the law of conservation of matter, which states that the "total quantity of matter in the universe is fixed and cannot be increased or decreased. And secondly, the law of conservation of energy which affirms that the total quan­tity of energy in the universe is likewise constant and can be neither created nor destroyed.

Nowadays, in the light of the theory of relativity, these two laws have become fused into one. We have seen a number of cases where one type of energy has been transformed into another. Whenever energy in one form is expended, an equal amount of energy in some other form takes its place. We have different units in which various forms of energy are measured, but after the conversion of work into heat, or chemical energy into work or electrical energy, the actual amount of energy is the same as before the change. This fact which is one of the fundamentals of physics is known as the law of the Conservation and Transformation of Energy.

Note

¹ as being separate and distinct from one another -- как отличающиеся друг от друга и существующие раздельно

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Listen and read words and word combinations to be re­membered:

relativity [,relə'tiviti] отно- destroy [dis'troi] разрушать

стельность support [se'po:t] поддерживать

convert [kən'və:t] превращать - expend [iks'pend] pacходовать

alter ['o:ltə] изменять accept [ak'sept] принимать

affirm [ə'fə:m] утверждать simplify ['simplifai] упрощать

create [kri'eit] создавать state [steit] констатировать

fuse [fju:z] зд. объединить, слить

to put forward выдвигать

the theory of relativity теория относительности

a number of ряд

to become fused слиться, объединиться

in some other form в другой форме

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