Spec Weight

#530 / Fluids Easy

Consider a certain fluid has a specific gravity of 1.9. What is its specific weight in lbf/ft^3?

Expand Hint
Specific weight, or unit weight, is a material’s weight per unit volume.
$$$\gamma =\rho g$$$
where $$\gamma$$ is specific weight, $$\rho$$ is density, and $$g$$ is gravity.
Hint 2
The specific weight of water at standard conditions is $$62.4\:lbf/ft^3$$ .
Specific Gravity, or Relative Density, is the ratio of a substance's density to a given reference material density. For liquids, water is commonly referenced.
$$$SG=\frac{\gamma }{\gamma_w}$$$
where $$\gamma_w$$ is the specific weight of water at standard conditions (a constant), and $$\gamma$$ is the specific weight. Note that specific weight, or unit weight, is a material’s weight per unit volume.
$$$\gamma =\rho g$$$
where $$\gamma$$ is specific weight, $$\rho$$ is density, and $$g$$ is gravity.

Since the specific weight of water at standard conditions is $$62.4\:lbf/ft^3$$ :
$$$1.9=\frac{\gamma }{62.4\:lbf/ft^3}$$$
$$$\gamma=(1.9)62.4\:\frac{lbf}{ft^3}=118.56\:\frac{lbf}{ft^3}$$$
$$$118.56\:\frac{lbf}{ft^3}$$$


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