Table of Contents
What Is Density?
Density is the ratio of an object's mass to its volume. It is an intensive property, meaning it does not depend on the amount of material. Each pure substance has a characteristic density that can be used for identification and quality control.
Density determines whether objects float or sink in fluids. Objects less dense than the surrounding fluid float; denser objects sink. This principle (Archimedes' principle) applies to ships, hot air balloons, and geological processes like mantle convection.
Density Formula
Common Material Densities
| Material | kg/m³ | g/cm³ |
|---|---|---|
| Air (STP) | 1.225 | 0.001225 |
| Water | 1,000 | 1.000 |
| Aluminum | 2,700 | 2.70 |
| Steel | 7,850 | 7.85 |
| Gold | 19,300 | 19.30 |
Frequently Asked Questions
Why does density matter?
Density is used in engineering for weight calculations, buoyancy analysis, material identification, and quality control. It is fundamental to fluid mechanics, meteorology, and geology.
Does temperature affect density?
Yes. Most materials expand when heated, decreasing density. Water is unusual in that it is densest at 4C, which is why ice floats.
What is specific gravity?
Specific gravity is the ratio of a substance's density to the density of water at 4C (1000 kg/m3). It is dimensionless and numerically equal to density in g/cm3.