Units and Significant Digits

Standards of Length, Mass and Time

MKS System (SI units)• Length – Meter ( 1/299,792,458 distance light

travels in a vacuum in one second• Mass – Kilogram (Mass of the International

Prototype Kilogram, a/k/a “Le Grande K”)• Time – Second (9,192,631,770 periods of the

radiation from cesium-133)

Prefixes for SI

10-24 yocto

10-21 zepto

10-18 atto

10-15 femto

10-12 pico

10-9 nano

10-6 micro

10-3 milli

10-2 centi

10-1 deci

1024 yotta

1021 zetta

1018 exa

1015 peta

1012 tera

109 giga

106 mega

103 kilo

102 hecto

101 deka

Significant DigitsSignificant Figures (Sig Figs)

123.4 Four Significant Digits

0.0012 Two Significant Digits

1,500 ? Significant Digits

1.50 x 103 Three Significant Digits

Adding/Subtracting

123.4 + 456 = 579

123.4 + 4.56 x 106 = 4.56 x 106

Only significant to the limit of any single term

Multiplying/Dividing

123.4 x 456 = 5.63 x 104

Only significant to the smallest number of significant digits in any single term