Exercise 13. Read the text and translate it without a dictionary
Text B
LEVER
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to another object. This is one example of the principle of moments. The principle of leverage can also be derived using Newton's laws of motion, and modern statics. It is important to notice that the amount of work done is the product of force and distance. The lever allows less effort to be applied to move an object a greater distance. For instance, to use a lever to lift a certain unit of weight with an effort of half a unit, the distance from the fulcrum to the spot where force is applied must be twice the distance between the weight and the fulcrum. For example, to halve the effort of lifting a weight resting 1 metre from the fulcrum, we would need to apply force 2 metres from the other side of the fulcrum. The amount of work done is always the same and independent of the dimensions of the lever (in an ideal lever). Levers are one of the six simple machines.
Notes:
fulcrum – точка опоры(вращения, приложения сил)
pivot – точка вращения(опоры)
derive – получать
Exercise 14. Translate the text with a dictionary in written form.
Text C
THE WHEEL AND AXLE
The wheel and axle is the first in the list of six simple machines. It has been used from ancient times. It first was identified by Renaissance scientists who studied Greek texts. Ancient Greeks used the wheel and axle to lift different loads. It consisted of a windlass connected to a cylindrical barrel or axle via a pulley. This provided mechanical advantage to wind up a rope and lift a load.
The wheel and axle machine is an assembly formed by two disks or cylinders of different diameters mounted so that they rotate together around the same axis. During this process a force is transferred from one to the other. Forces applied to the edges of the two disks or cylinders provide mechanical advantage. There is a bearing in this assembly which supports the rotation of the axle.
When used as the wheel of a cart the smaller cylinder is the axle of the wheel, but when used in a windlass, winch and other similar applications the smaller cylinder may be separate from the axle mounted in the bearings. It cannot be used separately.
This system is a version of the lever where loads are applied tangentially to the perimeters of the wheel and axle that are balanced around the hinge which is the fulcrum. The mechanical advantage of the wheel and axle is the ratio of the distances from the fulcrum to the applied loads, or what is the same thing the ratio of the radial dimensions of the wheel and axle. It is also can be computed as the ratio of the resistance to the effort. The larger the ratio is, the greater the multiplication of force or torque created or distance achieved is. By varying the radii of the axle and (or) wheel any amount of mechanical advantage may be gained.
Notes:
via – через посредство
windlass – лебедка
tangentially – по касательной
Unit 2
Grammar:
Tenses;
Active and Passive.
Exercise 1. Work out the following sounds:
[qV] compose, motion, follow, know, process
[Iq] gear, linear, near
[aV] allow, about, round, housing, ground, output, amount
Exercise 2. Match the transcription to the words given below and define their meanings:
| 1. ['buSIN] | 1. slide | 1. вес |
| 2. [maVnt] | 2. weight | 2. прямой |
| 3. [weIt] | 3. suspension | 3. втулка |
| 4. [streIt] | 4. oscillation | 4. место соединения |
| 5. [sq'spenS(q)n] | 5. bushing | 5. скользить |
| 6. [draIv] | 6. mount | 6. устанавливать |
| 7. [PsI'leIS(q)n] | 7.drive | 7. транспортное средство |
| 8. [slaId] | 8. vehicle | 8. колебание |
| 9. [GOInt] | 9. straight | 9. привод |
| 10. ['vJIk(q)l] | 10. joint | 10. подвеска |
Text A
MACHINE PARTS
Machines and mechanisms are composed of various units and parts. Parts which perform similar functions in different machines
(gears, axles, wheels, bearings, etc.) are referred to as general purpose parts.
Gears.
Gears or toothed wheels are positive type drives which are used to transmit motion between two shafts or a shaft and a component having linear motion by meshing of two or more gears. They have advantage over other drives like chains, belts, etc. in case of precision machines where a definite speed ratio is of importance and also in case where the driver and the follower are in close proximity; the disadvantage is that gears are more expensive to manufacture and their operating cost is also relatively high. Gears of different sizes are often used in pairs for a mechanical advantage, allowing the torque of the driving gear to produce a larger torque in the driven gear at a lower speed, or a smaller torque at a higher speed. The larger gear is known as a wheel and the smaller as a pinion. This is the principle of the automobile transmission, allowing selection between various mechanical advantages.
The ratio of the rotational speeds of two meshed gears is called the Gear ratio. Conservation of energy requires that the amount of power delivered by the output gear or shaft will never exceed the power applied to the input gear. Work equals the product of force and distance; therefore the small gear is required to run a longer distance and in the process is able to exert a larger twisting force or torque, than if the gears were the same size. There is actually some loss of output power due to friction.
Axles.
An axle is a central shaft for a rotating wheel or a gear. In some cases the axle may be fixed in position with a bearing or a bushing sitting inside the hole in the wheel or the gear to allow them to rotate around the axle. In other cases the wheel or gear may be fixed to the axle, with bearings or bushings provided at the mounting points where the axle is supported.
Axles are important structural components of a wheeled vehicle. The axles maintain the position of the wheels relative to each other and to the vehicle body. Since for most vehicles the wheels are the only part touching the ground, the axles must bear the weight of the vehicle plus any cargo, and also any acceleration forces between the vehicle and the ground.
Wheels.
A wheel is a round object that, together with an axle, allows low friction in motion by rolling.
Common examples are found in transport applications. More generally the term is also used for other circular objects that rotate or turn, such as a ship's wheel and flywheel.
The wheel (with an axle) is considered one of the simple machines and lies near the starting point of advanced human technology (advanced in comparison with even earlier mechanical innovations such as stone/bone knives and axes, scoops and shovels).
When wheels are used in conjunction with axles, either the wheel turns on the axle or the axle turns in a vehicle. The mechanics are the same in either case.
The low resistance to motion (compared to dragging) is explained as follows:
- the normal force at the sliding interface is the same;
- the sliding distance is reduced for a given distance of travel;
- the coefficient of friction at the interface is usually lower;
- bearings are used to reduce friction at the interface.
Bearings.
A bearing is a device to permit motion between two parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to the principle of their operation.
Common motions include linear/axial and rotary/radial motions. A linear one allows motion along a straight line. A rotary motion allows motion about a center, such as a wheel on a shaft or a shaft through a housing. Common kinds of rotary motion include both one-direction rotation and oscillation where the motion only goes through part of a revolution. Other kinds of bearings include spherical bearings such as ball joints which are used in car suspensions.
Exercise 3. Answer the following questions:
1. Why are some parts referred to as general purpose parts?
2. What are gears used for?
3. Why are gears of different sizes used in pairs?
4. What is a central shaft for a rotating wheel or gear called?
5. How may the axle be fixed in position?
6. What must the axles bear?
7. Where are common examples of wheels found?
8. What role does the wheel play in the advance of human technology?
9. What are the bearings used for?
10. How may bearings be classified?
Exercise 4. Translate the following words into Russian:
Gear, toothed, drive, shaft, mesh, chain, belt, size, torque, pinion, selection, deliver, rotate, twist, loss, bearing, bushing, mount, vehicle, weight, circular, flywheel, point, advanced, shovel, conjunction, resistance, slide, reduce, travel, movement, operation, include, straight, oscillation, revolution, joint, suspension.
Exercise 5. Translate from Russian into English:
Круглый, подвеска, зубчатая передача, устанавливать, вес, место соединения, маховое колесо, зубчатый, полный оборот, точка, транспортное средство, привод, колебание, передовой, втулка, вал, прямой, лопата, подшипник, зацеплять, включать, сопротивление, скручивать, ремень, действие, скользить, вращаться, размер, движение, уменьшать, вырабатывать, выбор, шестерня.
Exercise 6. Match the following words (A) with their definitions (B):
«A»
1. straight
2. torque
3. rotate
4. bearing
5. vehicle
6. shovel
7. slide
8. gear
9. revolution
10. suspension
«B»
1. an arrangement of toothed wheels connecting a motor with the work it has to do, enabling the motor to move at the same speed although the parts that are driven, e.g. the wheels, move faster or slower
2. to turn round a fixed point or axis
3. a tool with a broad usually square or rounded blade fixed to a handle, used for lifting or moving loose material
4. twisting force that produces rotation
5. to move smoothly along while touching a surface and remaining continually in contact with it
6. the part of a machine which turns on a fixed rod
7. without a bend or curve
8. one complete circular movement round a fixed point
9. a mechanism fixed to the wheels of a vehicle to lessen the effects of rough road surface
10. something in or on which people or goods can be carried from one place to another
Exercise 7. Define the tense of the predicates (Active Voice) and translate the sentences:
1. Machines transmit or modify energy to perform different tasks.
2. People have used mechanisms and machines since early times.
3. The actual mechanical advantage of a simple machine will usually differ from its theoretical value.
4. They were testing this new engine the whole day yesterday.
5. A machine normally requires some energy source to accomplish some sort of work.
6. We bought this device last week.
7. My friends are building a new house.
8. They have been building a new bridge since May.
9. First people did not know how to transform one kind of energy into another.
10. Before people invented modern machines they had used simple tools.
11. They will have built the plant by the end of the year.
12. At five in the evening he will be demonstrating the advantages of these new methods.
Exercise 8. Define the tense of the predicates (Passive Voice) and translate the sentences:
1. Damage in handling materials has been brought to the minimum.
2. A giant crane is being used at this construction site.
3. Large cranes are produced at our plant.
4. The production was increased after the new equipment had been installed.
5. Loads will be delivered in three days.
6. The plans to develop the district were being discussed during the meeting.
7. The plan will have been carried out by the end of the month.
Exercise 9. Open the brackets and use the proper tense:
1. The old concrete mixer (to be replaced) in several months.
2. A new crane (to be installed) at our plant now.
3. We (to study) laws of motion at the last lesson.
4. People (to use) simple tools since early times.
5. The engineers (to test) a new device in the laboratory now.
6. Some new types of hoisting equipment (to be manufactured) already.
7. The builders (to apply) many different hoisting mechanisms while constructing a multistorey building.
8. The crane (to be fitted) with a powerful diesel last month.
9. The truck (to have) a large capacity.
10. The site (to be prepared) before the crane (to arrive) there.