GE 121 – Engineering Design - 2009

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Engineering DesignGE121

UNITS

Lecture 9A

GE 121 – Engineering Design - 2009

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UnitsAll units should be standard Systeme Internationale (SI

or metric) gram, meter, liter, second, volt, watt, pascal, newton, etc. Or the approved abbreviation: g, m, l (or L), s, V, W, Pa, N,

etc. Units named after a person are capitalized when abbreviated but

not in full E.g. abbreviation for ampere is A not amp

Choose magnitude of units that make sense E.g.: km/hr for vehicle speeds rather than m/s in a report

dealing with transportation. SI standard increments are in multiples of 103

Femto, pico, nano, micro, milli, kilo, mega, giga, tera Abbreviations are lower case for <1 and capital for >1 (except

kilo): f, p, n, μ, m, k or K, M, G, T E.g. 51 mm NOT 5.1 cm

Make sure your units are consistent or there may be devastating results

GE 121 – Engineering Design - 2009

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Units

Base UnitsLength (L)

SI: km, m (meter), mm, etc.Time (T)

SI: s (second)Use fractional seconds (ms or microseconds) but

not ks or Msminute, hour, day, week, etc.

Mass (M)SI: g (gram), kg, ng

GE 121 – Engineering Design - 2009

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Derived Units

Area (L2)SI: hectare, m2, etc.Acres: this is an exception since it is in

widespread use in western CanadaVolume (L3)

SI: m3, L or l, mL, etc.

GE 121 – Engineering Design - 2009

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Derived Units

Speed (L/T)SI: m/s, km/hr, etc.

Acceleration (L/T2 or LT-2)SI: m/s2 or ms-2

GE 121 – Engineering Design - 2009

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Conversions

• a systematic approach is best to eliminate errors

e.g. Convert 6.7 in to millimeters.

6.7 in =25.4 mm

1 in6.7 in

= (6.7)(25.4) mm= 170.18 mm= 1.7 × 102 mm

GE 121 – Engineering Design - 2009

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5 furlongfortnight

× 1 fortnight14 days

ConversionsGiven the conversions 1 furlong = 220 yards, 1 m = 1.097 yards, 1 fortnight = 14 days, calculatethe speed in m/s of an animal which moves at 5 furlongs/fortnight.

5 furlongs/fortnight =220 yardsfurlong

1 m1.097 yards

= (5)(220)/((1.097)(14)(24)(3600)) m/s= 8.2898 × 10-4 m/s= 8 × 10-4 m/s or 800 μm/s

1 day24 hours

1 hour3600 s

GE 121 – Engineering Design - 2009

Units

Units

Conversions

Your car has a highway mileage of 35 mpg (miles/US gallon ). What is its mileage in L/100 km?

(1 mile = 1.6093 km)(1 US gallon = 3.7854 L)

Ans: 6.7 L/100 km