Ch 7 Dimensions, Units, And Conversions Flashcards
Dimensions
Describe physical quantities
Are INDEPENDENT of units
Book definition of a measurement
Comparisons of how many x units are in a physical quantity
Characteristics of engineer method
- Need: recognition/understanding of problem
- Know: data and sketch diagram
- How: select appropriate theory
- Solve: and check results
Freehand problem guidelines
- Engineer paper
- Legible
- Easy to follow
- Plenty of space
- Divide problem with horiz line
- Make diagrams
- Use proper symbols
Units
Describe magnitude of measurable quantities
Arbitrary
Fundamental units
m kg s Degree A cd (candela for brightness) mol
Mechanical dimension system
Length (l) Time (t) Mass (m) Force (F) Sometimes temperature
Absolute dimension system
Dimensions not affected by gravity
L
t
m
Gravitation dimension system
Simplification of weight computations
l
t
F
3 MVP fundamental unit systems
MKS
US Customary
Engineer system
3 class of units
- Base units
- Supplementary
- Derived
Bad units
Length: meter Mass: kg Time: s Electric intensity: A (ampere) Temperature: K Amount: mol Luminous intensity: cd
Supplementary units
Plane angle: radian (rad)= division between 2 radii of a circle that is cut off on a circumference of an arc equal length to the radius
Solid angle: steradian (sr)= has vertex in center of sphere
Engineer system
Mass= pound-mass (lbm) Length= ft Time= s Force= lbf
5 step method for unit conversions
- Write identity starting withe the quantity you’re converting
- Recall appropriate conversion factor
- Arrange equality for desired unit is in numerator
- Multiply the two identities
- Consider sig figs
