Quick Calculation – Specific Gravity from Specific Weight If an oil has specific weight 7.85 kN/m^3, its specific gravity (relative to water at about 9.81 kN/m^3) is SG = 7.85 / 9.81 ≈ 0.8.

Introduction:
Specific gravity provides a fast, unitless comparison of a fluid’s heaviness relative to water. Converting from specific weight to SG requires only a simple ratio, making it common in quick field estimates.

Given Data / Assumptions:

• Oil specific weight gamma_oil = 7.85 kN/m^3.
• Water specific weight gamma_water ≈ 9.81 kN/m^3 at standard reference.
• Same gravitational acceleration for both fluids.

Concept / Approach:

By definition, SG = gamma_oil / gamma_water. Because both have units of kN/m^3, SG is dimensionless. Values less than 1 imply the liquid is lighter than water and typically floats; values greater than 1 imply it is heavier and tends to sink.

Step-by-Step Solution:

Verification / Alternative check:

Using densities gives the same result since SG = rho_oil / rho_water and gamma = rho * g cancels g.

Why Other Options Are Wrong:

1 corresponds to water; 1.2 and 1.6 indicate a heavier-than-water liquid; 0.98 is too close to water and inconsistent with the given 7.85 kN/m^3 value.

Common Pitfalls:

Mixing up specific weight with density; forgetting to use water at the appropriate reference value; reporting SG with units.

Final Answer:

0.8