세번째, 비중 이야기- “1g”의 정의(定義) ?

[유기종]

: CGS 단위계⁽¹⁾에서 질량의 기본 단위. 4℃(엄밀하게는 3.98℃ ⁽²⁾)의 물 1㎝³의 질량 값.

 단위는 그램(gram), 기호는 “g”.

⁽¹⁾: CGS 단위계⇒ (CGS system of units), 길이의 단위를 센티미터(centimeter, 기호; ㎝), 질량의 단위를 그램(gram, 기호; g), 시간의 단위를 초(second, 기호; s)를 기본으로 하여, 물리량을 표현하는 단위계이다. 오늘날에는 국제적으로 권장하는 MKS 단위계와 대조적으로 사용하는데, MKS 단위계는 길이의 단위를 미터(meter, 기호; m), 질량의 단위를 킬로그램(kilogram, ㎏), 시간의 단위를 초(second, 기호: s)를 기본단위로 사용한다.

[참조-1]

The centimeter-gram-second system of units (abbreviated CGS or cgs) is a variant of the metric system based on the centimetre as the unit of length, the gram as the unit of mass, and the second as the unit of time.

From Wikipedia, the free encyclopedia

⁽²⁾ : 4℃⇒ 엄밀하게는 3.98℃

[참조-2]

Water also differs from most liquids in that it becomes dens as it freezes. The maximum density of water in its liquid from (at 1 atm) is 1,000 kg/m³ (62.43 lb/cu ft); that occurs at 3.98℃ (39.16℉). The density of ice is 917 kg/m³ (57.25 lb/cu ft). Thus, water expands 9% in volume as it freezes, which accounts for the fact that ice floats on liquid water.

From Wikipedia, the free encyclopedia

[참조-3]

The reference material can be indicated using subscripts: RD_{substance/reference}⁽³⁾,which means “the relative density of substance with respect to reference”. If the reference is not explicitly stated then it is normally assumed to be water at 4℃ (or, more precisely, 3.98℃, which is the temperature at which water reaches its maximum density). In SI units, the density of water is (approximately) 1000 kg/m³ or 1 g/cm³, which makes relative density calculations particularly convenient: the density of the object only needs to be divided by 1000 or 1, depending on the units.

From: W https://en.wikipedia.org/wiki/Relative_density

⁽³⁾: RD_{substance/reference}⇒ Relative density(RD) or specific gravity (SG) is a dimensionless quantity, as it is ratio of either of densities or weights “RD=ρ_substance/ρ_reference” where RD is relative density, ρ_substance is the density of substance being measured, and ρ_reference is the density of the reference. (By convention ρ, the Greek letter rho, denotes density.)

From: W https://en.wikipedia.org/wiki/Relative_density