Specific gravity is defined as

Specific gravity is defined as

• A. The ratio of a substance's density to the density of water
• B. The ratio of a substance's density to air density
• C. The ratio of a substance's mass to its volume
• D. The density of a substance at standard temperature

Answer: (A)

Specific gravity is a dimensionless ratio that compares how dense a material is to the density of water. It is defined as the density of the material divided by the density of water (SG = ρ_material / ρ_water). Because it’s a ratio, the units cancel, leaving a pure number. Water serves as the standard reference, so you can tell how heavy or light something is for its size: SG > 1 means the material is denser than water and will tend to sink; SG < 1 means it’s less dense than water and may float. The density-to-air ratio isn’t used for specific gravity, and density itself (mass per volume) isn’t a ratio. Density at a standard temperature doesn’t reference water, so it isn’t what specific gravity measures either.

Specific gravity is a dimensionless ratio that compares how dense a material is to the density of water. It is defined as the density of the material divided by the density of water (SG = ρ_material / ρ_water). Because it’s a ratio, the units cancel, leaving a pure number. Water serves as the standard reference, so you can tell how heavy or light something is for its size: SG > 1 means the material is denser than water and will tend to sink; SG < 1 means it’s less dense than water and may float. The density-to-air ratio isn’t used for specific gravity, and density itself (mass per volume) isn’t a ratio. Density at a standard temperature doesn’t reference water, so it isn’t what specific gravity measures either.