Summary:

Specific gravity, the ratio of an object's density to the density of a reference substance (usually water), provides insights into an object's buoyancy. A specific gravity less than 1 indicates that the object will float, with the percentage submerged equal to the specific gravity value. A specific gravity greater than 1 means the object will sink.

Highlights:

Definition: Specific gravity is the ratio of an object's density to a reference density, typically water (1000 kg/m³).
Units: Specific gravity is dimensionless (no units).
Buoyancy: For floating objects, the specific gravity equals the fraction of the object submerged. For example, a specific gravity of 0.6 means 60% of the object is submerged.
Sinking: Objects with a specific gravity greater than 1 will sink.
Alternative Reference Substances: While water is the common reference, specific gravity can be calculated using other liquids, such as oil.

Detailed Notes:

Specific gravity is defined as the density of an object divided by the density of a reference substance. Most commonly, water is used as the reference substance, with a density of 1000 kg/m³.

For example, gold has a density of 19,300 kg/m³, so its specific gravity is 19.3 (19,300 kg/m³ / 1000 kg/m³). Ketchup, with a density of 1400 kg/m³, has a specific gravity of 1.4. Since specific gravity is a ratio of densities, the units cancel out, making it a dimensionless quantity.

The practical significance of specific gravity lies in its relationship to buoyancy. For objects that float, the specific gravity directly indicates the percentage of the object's volume that will be submerged in the reference liquid. If a wooden cube has a specific gravity of 0.2, 20% of its volume will be submerged when floating in water. Ice, with a specific gravity of approximately 0.92, has 92% of its volume submerged, explaining why the majority of an iceberg lies beneath the water's surface.

If an object's specific gravity exceeds 1, it signifies that the object is denser than the reference liquid and will sink. Even if fully submerged, the object's volume cannot exceed 100% submersion.

While water is the typical reference substance, specific gravity can be calculated using other liquids. For instance, the specific gravity of a wooden block with a density of 638 kg/m³, when placed in oil with a density of 850 kg/m³, is calculated using the oil's density as the reference. In this case, the specific gravity is 638 kg/m³ / 850 kg/m³ = 0.75. This indicates that 75% of the wood's volume will be submerged in the oil.