M. Ibbotson - Professional english in use engineering (794233), страница 20
Текст из файла (страница 20)
How docs it provide a ml'Chanic;JIadvantage, and how great is the advantage?Professio nal English in Use Engineering73IIJ Moving parts-Angular motionIf a spanner is used to tighten a bolt, one end remains in thesame position on the bolt, while the other end turns. This typeof motion, where one end of a component pivots while the otherend follows the arc of a circle, is called angular motion. Anexample is a flap on an aircraft wing, which can be moved todifferent positions.
The point at the centre of angular motion iscalled the axis of rotation (or axis) . We say that the motionoccurs about the axis (around it) .axisIIIIIIIIIIII11Angular motionThe speed of angular motion is measured as angular velocity, and increases in angularvelocity are measured as angular acceleration.-Rotary and reciprocating motionWhen angular motion is through 360 degrees, it is called a revolution (or rotation). Whenmoving parts of machines, such as wheels, turn through complete revolutions - once, severaltimes, or for continuous periods- we say they revolve (or rotate) . The rotational velocity ofrevolving parts, or rotating parts, is measured in revolutions per minute (rpm) - often calledrevs per minute. The motion of revolving parts is called rotary motion.Rotary motion generates centrifugal force- that is, force which pushes outwards, away fromthe axis of rotation.
An increase in rotational velocity results in a higher centrifugal force.Some components move backwards and forwards. This type of motion is called reciprocatingmotion (or reciprocating action)- the component reciprocates. In machines, reciprocatingmotion is often converted (changed) to rotary motion. An example is a piston (see Unit 40).-Engine revsThe abbreviation for revolution- rev - is widely used to talkabout engines.
For example:•The rotational velocity of an engine is measured by arev counter.•High and low engine speeds are described as high revsand low revs.•Maximum engine speed can be controlled by a rev limiter.•If an engine's rev limit is exceeded, we say the engine isover-revved.•An engine designed to run at high speed is a high-revving engine.•When engine speed is increased momentarily, we say the engine is revved (or revved up).•We can say an engine is revved to a certain speed - for example, revved to 6,000 rpm.A rev counter-FrictionMoving parts cause friction . Friction is the force of resistance when two surfaces slide againsteach other. Frictional resistance is measured as the coefficient of friction.
This is the forcerequired to overcome friction in order to allow an object made of a specific material to slidealong the surface of another specific material.There are two types of friction. Static friction -sometimes called stiction -is the frictionalresistance between two surfaces that are at rest (not moving). It measures the force needed tostart a sliding action. Dynamic friction is the friction between two surfaces that are alreadysliding against each other. It measures the force needed to keep a sliding action going. Moreforce is needed to overcome static friction than to overcome dynamic friction .74Professional English in Use Engineering34.1Match the descriptions (1- 6) to the terms (a-f). Look at A and B opposite to help you.1 the speed of movement of a part which turns around a point2 pressure, exerted in an outward direction, due to rotary motion3 the rate of increase of speed of a part which turns around a point4 the point about which a part turns5 a turning movement6 movement backwards and forwardsabcdeangular motionangular velocityangular accelerationaxis of rotationreciprocating motionf centrifugal force34.2Complete the sentences using suitable forms of the words revolve or rotate.
Sometimesforms of both words are possible. Look at B opposite to help you. The first one has beendone for you............The measurement of ............. .r.~~.a.:t::~o.n~.1..velocity is rpm.2 As you can see, the wheel ................................................ at extremely high velocity.3 A recording device counts each ................................................ of the wheel.4 High-velocity ................................................
motion causes vibration.5 This wheel is the biggest ................................................ part in the machine.6 What's the speed of the turbine in ................................................ per minute?7 The braking system ensures the wheel ................................................ slowly.34.3Complete the description of an engine problem using words from C opposite.Norma.ll'j, -the engine .snouldn '-t be a.ble -to run fa..s-ter -tha.n i-ts ma.ximum(p ................................ ................................of B,DDD rpm.
lhe (2) ............................... ................................. .snould preven-t 1-t from exceeding -tha.-t limi-t. !'Ju-tsome-thing wen-t wrong, beca.u.se a.c.c.ording -to 1t1e rea.ding on 1t1e(~) ................................................................ , 1t1e engine (4) ............................... .................................
\D,?DD rpm - so i-t wa..s (?) ................................- ............................... .b<ja. significan-t ma.rgin. And since i-t '.s no-t .supposed -to be a.(lo) ................................ - ................................ engine, i-t's no-t designed -to copeWi-th 1t1o.se \1..\nd.s of .speeds .34.4Find expressions in D opposite with the following meanings.the measurement of friction2 the frictional resistance between surfaces that are already sliding against each other3 the frictional resistance between surfaces that are not yet sliding against each otherOve,r 1-o 11ou~Describe a machine you know about that contains parts which undergo angular motion and/or rotary motion.Professional English in Use Engineering75lliJ Energy-Forms of energyThe effects of energy can be seen, felt or heard in different ways, depending on the form ofenergy in question.
The main forms are listed below:•kinetic energy: energy in the form of movement - a type of mechanical energy•thermal energy: energy in the form of heat•electrical energy: the energy of an electric current•sound energy: energy in the form of noise•light energy: for example, light emitted from the sun or from a light bulb•chemical energy: energy within substances that can produce a chemical reaction•nuclear energy: energy from an atomic reaction.Energy cannot be created or destroyed, only converted from one form to another. Forexample, in a torch powered by batteries, chemical energy stored in the batteries is convertedto electrical energy, and the electrical energy is converted to light energy.Mechanical energy can be stored as potential energy.
An example is a load, lifted by a craneand suspended at a high level. The weight has the potential (in the future) to be released andallowed to fall, becoming kinetic energy. Energy can also be stored when a component iselastically deformed. This is called strain energy. An examp le is the spring in a watch, whichis wound up, then progressively unwinds.Note: For more on def or mation, see Unit 18. For more on stra in, see Un it 30.-Energy efficiencyMachines often convert an energy source,such as electricity, to another form of usefulenergy - in other words, energy used fora purpose.
For example, a motor convertselectrical energy (the energy source) intokinetic energy (useful energy). But it alsoconverts some energy into heat and noise.As this will be dissipated into the air, and notused, it is waste energy.A motor: electrical energy ~ useful kinetic energy~ wasted thermal and sound energyIf a machine converts a high percentage of energy into useful energy, it is efficient. Forexample, if a motor converts 75% of the electrical energy it consumes into kinetic energy,and wastes 25% as thermal and sound energy, it is seventy-five percent efficient.
Improvingefficiency - making efficiency gains - is a key focus in engineering.-Work and powerThe amount of energy needed to do a task - for example, lifting a load to a certain heightby crane - is called work. The amount of energy converted in order to perform tasks - inother words, the amount of work done- is measured in joules (J). If a force of one newton isrequired to keep an object moving, the work required to move that object over a distance ofone metre is equal to one joule.The speed, or rate, at which work is done is called power, and is measured in watts (W).One watt is one joule per second.
Power, in watts, is often referred to as wattage. A powerfulmotor will have a higher wattage than a less powerful one.76Professional English in Use Engineering35.1Make word combinations with energy using words from A and B opposite. Then match thecombinations with the descriptions (1-8).1 ................................ energy=2 ................................ energy =3 ................................ energy =4 ................................ energy=5 ................................ energy=6 ................................
energy =7 ................................ energy=8 ................................ energy=35.2energy stored within the liquids or solids in a batterymechanical energy in the form of movementpotential energy stored in a deformed materialenergy converted to the form required for a purposeenergy converted to a form that cannot be usedthe form of energy that shines, and can be seenthe form of energy that can be heardenergy that results in an increase in temperatureComplete the article about electric and diesel-electric locomotives using the words in the box.Look at A, B and C opposite to help you.chemicalconvertdissipatedefficiencyefficientelectricalformgamjouleskineticpowerpoweredAn electric locomotive is one that is(1) ................................
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
