M. Ibbotson - Professional english in use engineering (794233), страница 6
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Say what tolerances arcpermissible, both for production (not too tight du e to co sl), and for quality (not ton loose) .Say which parts require the tightest tnlcmntTS, and explain why.Professional English in Use Engineering21Numbers and calculations-Decimals and fractionsA manufacturer is thinking about giving both metric measurements (for example, millimetres)and imperial measurements (for example, inches) in its product specifications.
One of thecompany's engineers is giving his opinion on the idea in a meeting.'One problem is, when you convert from metric to imperial you no longer have wholenumbers - you get long decimal numbers . For example, one millimetre is nought pointnought three nine three seven inches as a decimal. So to be manageable, decimals have to berounded up or down. You'd probably round up that number to two decimal places, to giveyou zero point zero four. Now, you might say the difference is negligible- it's so small it'snot going to affect anything. But even if it's just a tiny fraction of a unit- one hundredth ofan inch (1/100), or one thousandth of an inch (1/1000)- and those numbers are then used incalculations, the rounding error can very quickly add up to give bigger inaccuracies.'Note: See Appendix Ill on page 100 fora list of metric and imperial units.-IMM=0 .o3q 37 if!Ghes "" 0 .0 4 if!GhesAddition, subtraction, multiplication and divisionDuring a TV programme about garden design, the presenter is explaining the calculationsrequired to make a large setsquare which can be used for setting out.To mal<:.e one of -these, 'jOO need -to use P'jfuagora..s 's lheorem.
So, a <jUicl<:. geome-tr'jlesson. tv\easure a leng-th of -timber for one of -the sides ad1acen-t -to -the right-angle.I 've made This :, fee-t long. lhe.n :>qJafe. -thai" number -:,WIUH:.iplle.! b'j :, e.ljUo.ls 9. lhe.ndo -the same Wifu -the o-ther side ad1acen-t -to -the right-angle. I 've made This one 4fee-t long. Worl<:. ou-tthe.ihose -two numbers -root of~uo.re.so if Iofis 1'=>. lhe.n worl<:. ou-t the. SUWI ofI'=> plus 9 is 2?. lhe.n, calcula-te the.
~uo.re.-thai". So, 4 ti~nes 4o.c:ld I'=> to 9fua-t. lhe s<jUMe roo-t of 2') is ?. lha-t means -the longes-t side -h'jpo-tenuse --theneeds -to be ') fee-t long. And i-t doesn '-t matter wha-t leng-th '::lou mal<:.e-the -two ad1acen-t sides -if -the s<juare of -the h'jPoi"enuse is ~Ieach of -the adiacen-t sides,o.c:lde.!i.o-the S<jUMe oft~the.r, '::lou '11 have a perfec-t nght-angle .A large setsquare for setting outNow 'jOU can also s-tart b'j mal<:.ing -the h'jpoi"enuse, s<juare fue leng-th of fua-t, -thensubi.ro.d one frOWIless I'=> Is 9.
And -the S<jUMemal<:.e one of -the o-ther sides, S<jUMe -the leng-th of -thai", and -then-the o-ther. ~or This e x ample, -tha-t would be 2? W~lnus I'=>. So, 2?9 is :,, Which gives me fue remaining side . Al-temaTivel'j, 'jOO can mal<:.e bofu -the- mal<:.e fuem -the same leng-th. So, -tal<:.e -the S<juare of fueh'jpoi"enuse, which is 2?, divide. -tha-t b'j 2, which is \2.?, -then war\<:. ou-t fue S<jUMe roo-t ofroo-t ofad1acent sides ~uo.l\2 .?, whichre<juires a calcula-tor! lha-t's wh'j i-t's easies-t -to use a :,-4-') -triangle, lil<:.eThis, Which convenienii'j worl<:.s wifu whole numbers.
And fua-t 's also Wh'j I 'm measuringl~lo.\, because :, fee-t b'j 4 fee-t b'j ') fee-t is a pracTical siz...e -to war\<:. wifu.22Professional English in Use Engineeringin8.1Write the numbers in words. Look at A opposite to help you.1.7932 1/100 mm3 1/1000 mm4 08.2millimetremillimetre................................ or ............................... .Complete the descriptions of the numbers using words from A opposite.1 0.25 = %The first number is a decimal, and the second is a2 0.6368 "'0.637The second number is ................................................................
to three3The second number is ................................................................ to one7.5278 "' 7.54 8,26,1545 Error: 0.00001%6 0.586 kg X 9,000 = 5,274 kg0.59 kg8.3X9,000 = 5,310 kgThis difference is the result of a ............................... .Complete the calculations using the words in the box. Sometimes there is more than onepossible answer. Look at B opposite to help you.dividedlessmmusmultiplied14 + 8 = 222 100 X 20 = 2,0003 7 X 11 = 774 400 + 8 =505 95 + 2 = 976 82 = 647 50-30 = 208 ~100 = 109 112=12110 48- 12 = 368.4The numbers aren't fractions or decimals.They're ................................
numbers.The error is so small that it's ................................ .plussquaresquare rootsquaredsubtractswntimesFourteen ................................ eight equals twenty-two.One hundred ................................ twenty is two thousand.Seven ................................ by eleven equals seventy-seven.Four hundred ................................ by eight equals fifty.The ................................
of ninety-five and two is ninety-seven.The ................................ of eight is sixty-four.If you ................................ thirty from fifty, it equa ls twenty.The ................................ of a hundred is ten.Eleven ................................ is a hundred and twenty-one.Forty-eight ................................ twelve equals thirty-six.Use your knowledge of basic geometry to complete the sentences. Use one or two words fromB opposite to fill each gap.1 The ................................ of the three angles in a triangle equals 180 degrees.2 The area of a circle is equal to the ................................ of its radius ................................
3.14.3 The area of a right-angle triangle is equal to the length of one adjacent side, ............................... .the length of the other adjacent side, ................................ two.4 The length of each side of a square is equal to the ................................ of the square's area.5 If each angle in a triangle is 60°, then the lengths of its sides are ................................ .Ov~r ..f-o J:iou ~Write down a few examples of some calculations you did recently, or ones that you dofrequently, and then explain them.Professional English in Use Engineering23Area, size and mass-AreaThe textbook extract below looks at different aspects of area.The sizes of electrical wires are specified by a number which gives an area in squaremillimetres.
For example, in a home, a 6 mm2 wire may be specified to supply an electricoven in a kitchen . This number gives the cross-sectional area of the conductor. Increasing thecross-sectional area allows the conductor to carry more current safely, without overheating.---'<-------\---conductorinsulationr----+---1--radius: 1.38 mmCross-sectional area = nr2= 3.14 x 1.382 = 6Cross-section of 6 mm 2 wireIn high-voltage power lines, it is not only thecross-sectional area of conductors that isimportant, but also their surface area - theamount of surface that is in contact withthe air, to allow cooling. Therefore, insteadof using single cables with large sectionsfor each conductor, power lines often usegroups of two, three or four small-sectioncables, to give more surface area than asingle, large-section cable.-Weight, mass, volume and densityIn everyday language, the term weight means how heavy things are (how much they weigh),and grams and kilograms are used as units of weight.
But in physics and in engineering,grams and kilograms are units of mass. Whether an object is on earth -where it is subjectedto gravity (the pull of the earth) - or floating weightless in space, its mass is always the same.The mass of an object depends on:•the volume of the object, measured in cubic metres (m3 ) -as an object's volume increases,its mass increases•the density of the object, measured in kilograms per cubic metre (kg/m3 ) - as densityincreases, mass per unit of volume increases.The mass of an object is the object's volume multiplied by its density.
The weight of an objectis the force exerted on the object's mass by gravity.Some materials are very dense, and therefore very heavy. An example is lead (Ph), which hasa density of 11,340 kg/m 3 • Other materials, such as expanded polystyrene (which can have adensity as low as 10 kg!m 3 ), are very lightweight.24Professional English in Use Engineering9.1The component below is made of mild steel.
It has a radius of 40mm and it is 1,200mm long.Complete the calculations using the words in the box. Look at A and B opposite to help you.cross-sectional areadensitysurface areamassvolume(1) ................................ of mild steel: 7,850kg/m 3(2]................................ : nr2 = 3.14 x 402=5 024mm 2 = 0.005024m 2(3) ................................ : 0.005024 m 2 x 1.
2m=0 .0060288 m 3(4) ................................ : 0.0060288m 3 x 7,850kg/m 3=Circumference: 2nr0.251 m=3.14 x 40mm=251 mm=47.32608kgTotal (5) ................................ to be painted: 0.251 m x 1.2m + 0.005m 2 + 0.005m2 = 0.311 m 29.2Now write the whole words for the unit abbreviations in the calculation in 9.1 above.Look at A and B opposite to help you.
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