On This Page
Overview
Density is mass per unit volume. It describes how tightly matter is packed into a space. Density is a key property in fluids, materials, buoyancy, planetary science, engineering, and everyday comparisons of substances.
Mass per Volume
Density compares mass with volume. A substance with high density contains more mass in the same volume than a substance with low density.
Material Property
Density can help identify materials because different substances often have characteristic densities under given conditions.
Floating and Sinking
An object tends to float in a fluid if its average density is less than the fluid's density. It tends to sink if its average density is greater.
Temperature Effects
Density can change with temperature because materials expand or contract. Warm fluids often become less dense and rise, while cooler fluids may become denser and sink.
Pressure Effects
Pressure can affect density, especially in gases. Compressing a gas increases its density by packing the same mass into a smaller volume.
Density in Fluids
Fluid density affects pressure with depth, buoyant force, flow behavior, and stratification in oceans and atmosphere.
Average Density
Objects made of multiple materials or containing empty spaces have an average density. A steel ship can float because its overall volume includes air, lowering average density.
Common Mistakes
A common mistake is assuming heavy objects always sink. Floating depends on average density compared with the fluid, not weight alone.
Why This Matters in Physics
Density helps explain buoyancy, pressure, materials, planetary interiors, fluids, gases, weather, ocean circulation, and engineering design.