机械工程导论完整PPT资料

volume (L), weight (lb), mass (kg)
6
2 UNIT SYSTEMS AND CONVERSIONS- Base and Derived Units
what is base units?
kilometer (km)
Why Why
ddAooeessbttahheesUUenniiutteendd iSStttaaittseessassttaafnnuddnooduuttaiinnmrreeettaaniinntiinnaggl ttqhheeuUUaSSnCCSSti??ty
Understand the need for proper bookkeeping of units when making engineering calculations and the implications of not doing so.
Convert numerical quantities from the United States Customary System to the System International d‘ Units, and vice versa.
One is simply meaningless without the other, and practicing engineers pay as close and careful attention to the units in a calculation as they do to the numbers.
CHAPTER2 Problem-Solving Skills来自1OVERVIEW
2
UNIT SYSTEMS AND CONVERSIONS
3
DIMENSIONAL CONSISTENCY
4
SIGNIFICANT DIGITS
5 AN ERROR OF UNITS ON THE WAY TO MAR 6 APPROXIMATION IN ENGINEERING
that
cannot
be
further
S76E8LF2-bSlitTerUrosDkY(LeA) NnDdRoEVwIEnW or expressed in terms of any simpler elements.
what is USCS and SI?
Engineers specify physical quantities in two different, but conventional, systems of units: the United States Customary System (USCS) and the International System of Units. Practicing mechanical engineers must be conversant with both unit systems.
7
PROBLEM-SOLVING METHODOLOGY
1
Vocabulary
➢ Torque 扭矩 ➢ thermal conductivity 热导率 ➢ shear stress 剪应力 ➢ fluid viscosity 流体的粘度 ➢ elastic modulus 弹性模量 ➢ kinetic energy 动能 ➢ Reynolds number 雷诺数
5
2 UNIT SYSTEMS AND CONVERSIONS- an example
Keeping Track of Units on Fright 143
In July of 1983, Air Canada Flight 143 was en route from Montreal to Edmonton. The Boeing 767 had three fuel tanks, one in each wing and one in the fuselage, which supplied the plane's two jet engines.
3
1 OVERVIEW--- The ability to be available in this chapter
After study, what should you be able to have?
Report both a numerical value and its unit in each calculation that you perform.
Check your equations and calculations to verify that they are dimensionally consistent.
Understand how to perform order-of-magnitude approximations.
4
2 UNIT SYSTEMS AND CONVERSIONS- Unit System
List the base units in the United States Customary System and the System International d‘ Units, and state some of the derived units used in mechanical engineering.
Boeing 767
How much fuel should be added ?
pounds (lb); kilograms
Total fuel
1.77 kg/L 1.77 lb/L
9000 liters 16,000 liters
Fuel in tanks 7682 liters (L)
22,300 kilograms (kg)
2
1 OVERVIEW----the important of unit
How important a unit is?
Each quantity in mechanical engineering has two components: a numerical value and a unit.