Specific Gravity

Specific gravity is a way of relating the density of an object to the density of water to determine whether or not the object will float.  The formula for specific gravity is given below:

If an object's specific gravity is less than one, then the object will float.  If the object has a specific gravity of greater than one, it sinks.  So dense objects sink in water and less dense objects float.  

Importance of Specific Gravity

Specific gravity is a very important concept in the water/wastewater field.  The specific gravity of a substance will determine where a compound can be found in water in case of a spill.  

Let's consider gasoline.  The density of gasoline is 0.6 g/mL and the density of water is 1.0 g/mL.  So the specific gravity of gasoline is:

Since its specific gravity is 0.6 (less than 1), gasoline floats in water.  So when a ship leaks gasoline into the water, the gasoline stays at the top of the water.

In contrast, the specific gravity of palmalive is 1.1, so it sinks in water.