Density

Beginner

Mass per unit volume.

Key relationρ = m/V

ρ = m/V, in kg/m³. It tells how tightly matter is packed. Water is 1000 kg/m³, air about 1.2, iron 7870.

Worked example

A 2 kg block of 0.001 m³ has ρ = 2000 kg/m³.

Common mistake

Check units: g/cm³ × 1000 = kg/m³.

In more detail

Density is mass per unit volume, ρ = m/V. It is measured in kilograms per cubic metre, and it decides whether an object floats or sinks in a fluid.

Oil floats on water because it is less dense.
Alcohol strength is checked by measuring density.
Ships float because the average density of the hull and air inside is lower than the density of seawater.

What is the density of water?

About 1000 kg/m³, or 1 g/cm³.

Does density depend on mass alone?

No. It depends on how much mass is packed into a given volume.

Which is denser, ice or water?

Water is denser than ice, which is why ice floats on top of a lake.