Page 31 - statbility for masters and mates
P. 31
Chapter 3
Density and speci®c
gravity
Density is de®ned as `mass per unit volume'. e.g.
The mass density of FW 1000 kg per cubic metre or 1.000 tonne/m3
The mass density of SW 1025 kg per cubic metre or 1.025 tonne/m3
The speci®c gravity (SG) or relative density of a substance is de®ned as the ratio of the weight of the substance to the weight of an equal volume of fresh water.
If a volume of one cubic metre is considered, then the SG or relative density of a substance is the ratio of the density of the substance to the density of fresh water. i.e.
SG or relative density of a substance Density of the substance Density of fresh water
or
The density of FW 1000 kg per cu. m
; SG of a substance Density of the substance in kg per cu. m
1000 Density in kg per cu: m 1000 SG
Example 1
Find the relative density of salt water whose density is 1025 kg per cu. m
Relative density Density of SW in kg per cu: m 1000
1025 1000
; relative density of salt water 1:025
