Engineering Design GE121

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Engineering DesignGE121

• UNITS
• Lecture 9A

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Units

• All 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 lt1 and capital
  for gt1 (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

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Base Units

• Length (L)
• SI km, m (meter), mm, etc.
• Time (T)
• SI s (second)
• Use fractional seconds (ms or microseconds) but
  not ks or Ms
• minute, hour, day, week, etc.
• Mass (M)
• SI g (gram), kg, ng

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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 Canada
• Volume (L3)
• SI m3, L or l, mL, etc.

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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

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Conversions

• a systematic approach is best to eliminate
  errors

e.g. Convert 6.7 in to millimeters.
6.7 in
(6.7)(25.4) mm 170.18 mm 1.7 102 mm
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Conversions
Given the conversions 1 furlong 220 yards, 1 m
1.097 yards, 1 fortnight 14 days,
calculate the speed in m/s of an animal which
moves at 5 furlongs/fortnight.
5 furlongs/fortnight
(5)(220)/((1.097)(14)(24)(3600)) m/s 8.2898
10-4 m/s 8 10-4 m/s or 800 µm/s
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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