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數學工具:向量,微積分
~The International System of Units(IS)
1.Units for three SI base quantities
Quantity Unit Name Unit quantities
Length meter m
Time second s
Mass kilogram kg
SI derived units are defined in terms of these base units
EX: SI unit for power watt(W)
1 watt=1W=1kg*m 2/s 3 (m 2~m的二次方 s 3~s的三次方)
因為P=dw/dt=F.dS/dt F~kg*m 2/s 2 (m 2~m的二次方 s 2~s的二次方)
dS~m
dt~s

2.The most frequently used prefixes(prefixes~字首)

Factor Prefix Symbol
10 9 giga- G
10 6 mega- M
10 3 kilo- K
10 -2 centi- C
10 -3 milli- m
10 -6 micro- u
10 -9 nano- n
10 -12 pico- p
10 -15 femto- f
~10( ?)為?次方
EX:1.27*10 9 watts=1.27 gigawatts=1.27 GW
2.35*10 -9 s=2.35 nanosecond=2.35 ns

3.Significant figures(有效位數)
例:地球半徑6.37*10 6 m
周長4.00238*10 4 km~4.oo*10 4 km <3位有效數字>
面積5.099*10 8 km 2~5.10*10 8 km 2
結論:Final results of caculations are often rounded to match the least number of signifcant figures in the given data

~Length,Time,and Mass
1650763 Kr-atom
1.Def:One menter => The length of the path traveled by light in a vacuum during a time interval of
1/299792458 of a second
the speed of light C=299792458 m/s
2.Def:One second => The time taken by 9192631770 oscillations of the light of a specified wave length
emitted by a cesium-133 atom

3.Def:One kilogram => The mass of a platinum-iridium cylinder 3.9 cm in height and in diamter(Fig 1-3)
4.Def:Order of magnitude of a number => The power of ten when the number is expressed in scientific
notation
EX:A=2.3*10 4 order of magnitude=4
B=7.8*10 5 order of magnitude=5
A=2.3*10 4 nearest order of magnitude=4
B=7.8*10 5 nearest order of magnitude=6