What is Specific Gravity?

What is Specific Gravity?

• A. The ratio of the density of a solid or liquid to the density of water.
• B. The sum of densities of solids and liquids.
• C. Mass divided by volume.
• D. Weight per unit area.

Answer: (A)

Specific gravity is a dimensionless way to compare how dense a material is to the density of water. It’s the ratio of the material’s density to the density of water, so SG = rho_material / rho_water. Because water’s density is about 1 g/cm^3 at standard conditions, the number you get for SG often matches the material’s density in those units. If the SG is greater than 1, the material is denser than water and would tend to sink; if it’s less than 1, it’s less dense and would tend to float. This makes it useful for quick comparisons without carrying units. It’s not mass divided by volume (that’s density), it’s not weight per unit area, and it isn’t a sum of densities. For example, a substance with density 2.5 g/cm^3 has SG ≈ 2.5, while one with 0.9 g/cm^3 has SG ≈ 0.9.

Specific gravity is a dimensionless way to compare how dense a material is to the density of water. It’s the ratio of the material’s density to the density of water, so SG = rho_material / rho_water. Because water’s density is about 1 g/cm^3 at standard conditions, the number you get for SG often matches the material’s density in those units.

If the SG is greater than 1, the material is denser than water and would tend to sink; if it’s less than 1, it’s less dense and would tend to float. This makes it useful for quick comparisons without carrying units.

It’s not mass divided by volume (that’s density), it’s not weight per unit area, and it isn’t a sum of densities. For example, a substance with density 2.5 g/cm^3 has SG ≈ 2.5, while one with 0.9 g/cm^3 has SG ≈ 0.9.