English for students of physics. Часть 1 (110

small but persistent. It causes the axis of the Earth to 17 _____, about one revolution every 25,800 years.

I As seen from the Earth, the Sun passes through the plane of the Equator twice each year. These points are called the equinoxes, and on the days of the equinoxes the hours of daylight and night are equal. From antiquity it has been known that the point in the sky where the Sun intersects the plane of the Equator is not the same each year but rather drifts very slowly to the west. This ancient observation, first explained by Newton, is due to the precession of the Earth's axis. It is called the precession of the equinoxes.

III. Which paragraph says that...? Explain your choice.

1.Kinetic energy is required for orbital motion.

2.Friction at the point of contact will require the centre of mass to lower

itself.

3.Each year the point where the Sun crosses the Equator moves slightly to

the west.

4.Nutation represents by itself up and down oscillation.

5.Uniform circular motion is produced by the torque.

6.Inertial guidance is commonly used in navigation.

7.The wheel does not fall due to gyroscopic precession.

8.The axis of the Earth precesses due to the form of the planet.

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9. To resist changes in the direction of the axis of spin, spinning at the maximum frequency is required.

IV. Answer the questions:

-Why doesn't the wheel fall in spite of the fact that gravity applies a downward force on the wheel?

-What is the cause of nutation?

-Can you describe the motion of a spinning top?

-How does a gyroscope work?

-Why does the Sun apply its torque to the Earth?

-What causes the Earth's axis to precess?

-What does the precession of the equinoxes consist in?

-What other examples of gyroscopic precession can you give? Where else can it be used?

V. Speaking

-Make a short summary of the article (no more than 8 sentences).

-You are taking part in a popular scientific programme about mechanics. You are an experienced scientist who is explaining the basics to the journalist. Role-play the conversation. Try to be as short and informative as possible.

Unit IV. Hydroelectric Power

Hydroelectric power is electricity produced from generators driven by water turbines that convert the 1. _____ energy in falling or fast-flowing water to 2._____ energy.

In the generation of 3. _____ power, water is collected or stored at a higher elevation and led downward through large 4. ____ or tunnels (penstocks) to a lower elevation; the difference in these two elevations is known as the head. At the end of its passage down the pipes, the falling water causes turbines to 5.

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_____ . The 6. _____ in turn drive generators, which 7. ______ the turbines' mechanical energy into electricity. Transformers are then used to convert the alternating voltage suitable for the 8. ______ to a higher voltage suitable for long-distance 9. ______ . The structure that houses the turbines and generators, and into which the pipes or penstocks feed, is called the 10. _____.

Powerhouse, generators, transmission, turbines, convert, hydroelectric, mechanical, pipes, potential, rotate.

I Put the paragraphs into the right order. Explain your choice.

A.Falling water is one of the three principal sources of energy used to generate electric power, the other two being fossil fuels and nuclear fuels. Hydroelectric power has certain advantages over these other sources: it is continually renewable owing to the recurring nature of the hydrologic cycle and produces neither atmospheric nor thermal pollution. Hydroelectric power is a preferred energy source in areas with heavy rainfall and with hilly or mountainous regions that are in reasonably close proximity to the main load centres. Some large hydro sites that are remote from load centres may be sufficiently attractive to justify the long high-voltage transmission lines. Small local hydro sites may also be economical, particularly if they combine storage of water during light loads with electricity production during peaks.

B.In certain coastal areas, such as the Rance River estuary in Brittany, France, hydroelectric power plants have been constructed to take advantage of the rise and fall of tides. When the tide comes in, water is impounded in one or more reservoirs. At low tide, the water in these reservoirs is released to drive hydraulic turbines and their coupled electric generators.

C.Hydroelectric power plants are usually located in dams that impound rivers, thereby raising the level of the water behind the dam and creating as high

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a head as is feasible. The potential power that can be derived from a volume of water is directly proportional to the working head, so that a high-head installation requires a smaller volume of water than a low-head installation to produce an equal amount of power. In some dams, the powerhouse is constructed on one flank of the dam, part of the dam being used as a spillway over which excess water is discharged in times of flood. Where the river flows in a narrow steep gorge, the powerhouse may be located within the dam itself.

D. In most communities, electric-power demand varies considerably at different times of the day. To even the load on the generators, pumped-storage hydroelectric stations are occasionally built. During off-peak periods, some of the extra power available is supplied to the generator operating as a motor, driving the turbine to pump water into an elevated reservoir. Then, during periods of peak demand, the water is allowed to flow down again through the turbine to generate electrical energy. Pumped-storage systems are efficient and provide an economical way to meet peak loads.

II Fill in the right terms:

-Falling water, fossil and nuclear fuels are _______.

-Water is collected or stored at a higher ______ and led downward through large pipes to a lower _______ .

-To create a high head it is necessary to raise the level of the water behind the _____.

-Transformers convert the _____ ______ suitable for the generators to a higher ______ suitable for transmission.

-The potential power produced from a volume of water is _______ to the working head.

-In mountainous areas ______ may be located within the dam itself.

-The turbine ______ water into an elevated reservoir.

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- In coastal areas people have learnt to _____ ______ of the rise and fall of tides.

III Explain the following: a penstock, the working head, an off-peak period, to meet peak loads, to even the load on, a spillway, to take advantage of, a load centre.

IV Say whether the statements are true or false:

1.Water turbines are driven by generators.

2.The rising water level causes turbines to rotate.

3.In the generation of hydroelectric power, water should be moved downward to a lower level.

4.Transformers are used to convert the mechanical energy into

electricity.

5.A high-head installation requires a bigger volume of water than a low-head installation to produce an equal amount of power.

6.Where the river flows in a narrow steep place, the powerhouse should be constructed on one flank of the dam.

7.Pumped-storage systems are used to vary electric power demand.

8.A powerplant should be as close to the main load centre as possible.

V Answer the following questions:

-What are the key “participants” of the process of generation of energy? What does it (the process) involve?

-What is the role of transformers? Why are they important?

-What is important to know about the location of powerplants?

-What equipment is used to meet the variation of electric power

demand?

-What system is used in certain coastal areas?

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- What are the advantages of falling water over other sources of energy?

VI Speaking. You are an expert in hydroelectric power. You are taking a group of tourists on a tour around the powerplant you work for. Tell them about its location, structure and the way the plant operates.

Unit V. The Law of Buoyancy and Naval Architecture

I Fill in the gaps with the terms given: metacentric, deadweight, magnitude, displacement, hydrostatic principles, submerged, law of buoyancy.

1 The A ______, discovered by the ancient Greek mathematician and inventor Archimedes, states that any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force the magnitude of which is equal to the weight of the fluid displaced by the body. The volume of displaced fluid is equivalent to the volume of an object fully immersed in a fluid or to that fraction of the volume below the surface for an object partially submerged in a liquid. The weight of the displaced portion of the fluid is equivalent to the B _________ of the buoyant force. The buoyant force on a body floating in a liquid or gas is also equivalent in magnitude to the weight of the floating object and is opposite in direction; the object neither rises nor sinks. For example, a ship that is launched sinks into the ocean until the weight of the water it displaces is just equal to its own weight. As the ship is loaded, it sinks deeper, displacing more water, and so the magnitude of the buoyant force continuously matches the weight of the ship and its cargo.

2 If the weight of an object is less than that of the displaced fluid, the object rises, as in the case of a block of wood that is released beneath the surface of water or a helium-filled balloon that is let loose in air. An object heavier than

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the amount of the fluid it displaces, though it sinks when released, has an apparent weight loss equal to the weight of the fluid displaced. In fact, in some accurate weighings, a correction must be made in order to compensate for the buoyancy effect of the surrounding air.

3 The buoyant force, which always opposes gravity, is nevertheless caused by gravity. Fluid pressure increases with depth because of the (gravitational) weight of the fluid above. This increasing pressure applies a force on a C ____

object that increases with depth. The result is buoyancy. The basis of naval architecture is found in Archimedes' principle. This law of buoyancy determines not only the draft at which a vessel will float but also the angles that it will assume when in equilibrium with the water.

4 A ship may be designed to carry a specified weight of cargo, plus such necessary supplies as fuel, lubricating oil, crew, and the crew's life support. These combine to form a total known as D ______. To deadweight must be added the weight of the ship's structure, propulsion machinery, hull engineering (nonpropulsive machinery), and outfit (fixed items having to do with crew life support). These categories of weight are known collectively as lightship weight. The sum of deadweight and lightship weight is E ______—that is, the weight that must be equaled by the weight of displaced water if the ship is to float. Of course, the volume of water displaced by a ship

is a function of the size of that ship, but in turn the weight of water that is to be matched by displacement is also a function of the ship's size. The early

stages of ship design, therefore, are a struggle to predict the size of the ship that the sum of all weights will require. The naval architect's resources include experience-based formulas that provide approximate values for making such

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predictions. Subsequent refinements usually produce accurate predictions of the ship's draft—that is, the depth of water in which the finished ship will float.

5 Accurately predicting a ship's draft is a necessary result of correctly applied F______ but is far from sufficient. If the many items of weight on a ship are not distributed with considerable precision, the ship will float at unwanted angles of heel (sideways inclination) and trim (endwise inclination). Nonzero trim angles may lift the tips of propeller blades above the surface, or they may increase the possibility that the bow will slam into waves during heavy weather. Nonzero heel angles (which tend to be much greater than trim angles) may make all human activity aboard difficult; moreover, they are dangerous because they reduce the margin against capsizing. In general, the avoidance of such inclinations requires an extension of Archimedes' principle to the first moments of weights and volumes: the collective first moment of all weights must equal the first weight moment of the water displaced.

6 A figure depicting the static stability of a ship shows the cross section of a ship that is floating at heel angle θ, caused by the placement of a weight (w) a certain distance (d) from the centre line. At this angle, the upsetting moment, calculated as w × d × cos θ, is equaled by the righting moment × GZ, ( is the symbol for displacement, and GZ is the distance from the centre of gravity [G] to the centre of buoyancy [Z]). Under these conditions, the ship is said to be in static equilibrium. If w is removed, the upsetting moment will become zero, and the righting moment will return the ship to its upright position. The ship is therefore judged to be stable. The moment will act in the stable direction only as long as the point M (the “metacentre,” the point where the buoyant force intersects the midplane) is above G (the centre of gravity of the ship and its contents). If M is below G, the forces of weight and buoyancy will tend to increase the angle of

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heel, and the equilibrium will be unstable. The distance from G to M, taken to be positive if M is above G, is called the transverse G ______ height.

7 A value for G_____ height is usually found only for the zero heel condition; hence, it is an accurate measure of stability only for small disturbances—for example, ones that cause heeling of no more than about 10°. For larger angles, the “righting arm,” GZ, is used to measure stability. In any stability analysis, the value of GZ is plotted over the entire range of heel angles for which it is positive, or restoring. The resultant curve of statical stability shows thereby the angle beyond which the ship cannot return to upright and the angle at which the restoring moment is at a maximum. The area of the curve between its origin and any specified angle is proportional to the energy required to heel the ship to that angle.

II Which paragraph states the following?

1.A metacentric height only works for small disturbances.

2.If the upsetting moment becomes zero, the ship regains its upright

position.

3.It is important to distribute the weight items of the ship with precision to avoid inclinations.

4.A submerged object rises if its weight is less than that of the displaced liquid.

5.Displacement is the weight that must be equaled by the weight of displaced water if the ship is to float.

6.The buoyant force is equivalent in magnitude to the weight of the floating object and is opposite in direction.

7.The buoyant force is closely connected with gravity.

III Answer the questions:

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-What does the law of buoyancy consist in?

-What does the buoyant force depend on?

-What is the buoyant force caused by?

-Which categories of weight should be taken into account in the construction of a ship?

-What else should be considered while making a ship's draft? What problems can be caused by trim and heel inclinations? What should be done to avoid them?

-In what conditions is the ship supposed to be in static equilibrium?

- What does the resultant curve of statical stability show?

IV Using the picture (Figure I) say what forces are at work in buoyancy.

- Write down a formula showing an object flowing in equilibrium (the sum of forces on the object is zero).

Figure I

-What does Figure 2 show?

Figure II

V. Speaking. What are the legends connected with the discovery of the Archimedes' Principle? How did he come to his discovery? What else is he famous for? Use your background knowledge or any

information source you need.

VI. Summarize the article in 5 – 7 sentences.

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