Units and Conversions

1
Units and Conversions
2
What is

• Ratio of an igloos circumference to its
  diameter?
• Eskimo p
• Time between slipping on a peel and smacking the
  pavement?
• 1 bannosecond
• 1000 aches?
• 1 killohurtz

3

• Quantity (Q)
• Numerical Value Units (U)
• Without the units to value has no meaning except
  as a ratio.

4
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

5
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

6
SI System

• Base units
• Length, meter
• Time, second
• Mass, kilogram
• Electrical current, ampere
• Temperature, kelvin
• Amount of substance, mole
• Luminous intensity, candela

7
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

8
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 ?

9
Rules for Using SI Units

• Look at section 6.6, pg 210
• Symbols and names
• Multiplication and division
• Numbers

10
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

11
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

12
US Customary System

• Base units
• Length, foot, ft
• Time, second, s
• Force, pound, lb
• Derived unit
• Mass, slug

13
American Engineering System

• Base units
• Length, ft
• Time, s
• Force, lbf
• Derived unit
• Mass, lbm, 32.174 lbm 1 slug

14
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