Understanding Units and Conversions in Measurement Systems
This guide explores the fundamentals of units and conversions in various measurement systems, including the International System of Units (SI) and the US Customary System. Discover the significance of base and derived units, learn about engineering and scientific notation, and understand the differences between coherent and noncoherent systems. We’ll also touch upon unique measurements like Eskimo π and bananoseconds, illustrating the creative aspects of quantification in everyday life.
Understanding Units and Conversions in Measurement Systems
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Presentation Transcript
What is • Ratio of an igloo’s circumference to its diameter? • Eskimo π • Time between slipping on a peel and smacking the pavement? • 1 bannosecond • 1000 aches? • 1 killohurtz
Quantity (Q) = Numerical Value * Units (U) Without the units to value has no meaning except as a ratio.
Types of dimensions • Fundamental or base, what system is built on • Derived, the ones that are built on the base dimensions • For mechanical systems we have length, time, and mass or force as base
SI System of Units (International System) • An absolute system (not gravity dependent) • Comes from the “metric system” or MKS • Base units: • Length: meter, m • Time: second, s • Mass: kilogram, kg Derived unit: Force, newton, N or kg m/s2
SI System • Base units: • Length, meter • Time, second • Mass, kilogram • Electrical current, ampere • Temperature, kelvin • Amount of substance, mole • Luminous intensity, candela
SI System • Supplemental Units: • Plane angle: radian, rad • Solid angle: steradian, sr • Derived Units: • See tables 6.4 and 6.5 on pg 207 • See figure 6.2 on pg 208 for relationships
SI System • SI System is a base 10 system • Use prefix to identify size of unit • 109 giga G • 106 mega M • 103 kilo k • 10-3 milli m • 10-6 micro μ • 10-9 nano η
Rules for Using SI Units • Look at section 6.6, pg 210 • Symbols and names • Multiplication and division • Numbers
Engineering Notation • Scientific notation: number between 0 and 1.0 times 10 to a power, example 2.334 * 105m • Engineering notation: number between 0.1 and 1000 times 10 to a power of 3, 6, 9, -3, -6, -9, etc., example 233.4 km or 233.4 * 103 m
Coherent and Noncoherent Systems Coherent systems: SI, US Customary No additional conversion factors needed Noncoherent systems: American Engineering System Additional conversion factor needed 1 lbf = 32.174 lbms2/ft
US Customary System • Base units: • Length, foot, ft • Time, second, s • Force, pound, lb • Derived unit: • Mass, slug
American Engineering System • Base units: • Length, ft • Time, s • Force, lbf • Derived unit: • Mass, lbm, 32.174 lbm = 1 slug
Effect • For equation F = ma • SI system N = 1 kg m/s2 • USC system lb = 1 slug ft/s2 • Am Engr System lbf = 32.174 lbm ft/s2
