Page 26 - ebook fluid mechanics_finalize

FLUID MECHANICS

2.2.2 Specific Weight or Weight Density.

Specific weight,  is defined as the weight per unit volume. It is denoted by the

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symbol  (omega) and SI units, N/m

weight, W
 =
volume, V

mg ( mass of fluid ) x Accelerati on due gravity
 = =
V Volume of fluid

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 = ρg (where g = 9.81m/sec ) .....(1.1)

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In SI units the specific weight of water is 9.81 x 1000 = 9810 N/m

2.2.3 Specific Gravity or Relative density.

Specific gravity, S is the ratio of the weight density of a fluid to the weight density of

a standard fluid (water) and for gases, the standard fluid (air). The weight of an equal
volume of water at 4 ºC.

 weight density of liquid
,
S( for liquids) = @
 , weight density of water
water

 weight density of gas
,
S( for gases) =
 , weight density of air
air

OR

 , density of liquid
S( for liquids) = @
 water , density of water

 , density of gas
S( for gases) = sub
 , density of air
air

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