What is Density?
Density tells you how much mass is packed into a given volume of a substance. It's why a small lead ball feels much heavier than a foam ball of the same size — lead is far denser.
Density is mass per unit volume: ρ = m/V, measured in kg/m³ or g/cm³. Denser materials pack more mass into the same space.
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Step-by-step worked examples
A rock has a mass of 300 g and a volume of 100 cm³. Find its density.
ρ = m/V = 300/100 = 3 g/cm³
A metal block has a mass of 5400 kg and a volume of 2 m³. Find its density.
ρ = m/V = 5400/2 = 2700 kg/m³
An object has a density of 0.8 g/cm³ and a volume of 50 cm³. Find its mass.
m = ρ × V = 0.8 × 50 = 40 g
Flashcards
Quick quiz
Q1.A 200 g object has a volume of 50 cm³. Its density is...
Q2.Which of these floats on water (density 1 g/cm³)?
Q3.What is the unit of density in SI?
Q4.A liquid has a density of 0.9 g/cm³ and a volume of 200 cm³. Its mass is...
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Common mistakes
Heavier objects always sink. — Correct: Whether an object sinks depends on density, not just weight — a huge but hollow steel ship floats.
Density and mass are the same. — Correct: Density is mass per volume; two objects of equal mass can have very different densities.
Volume units don't need converting. — Correct: Make sure mass and volume units match (e.g., g with cm³, or kg with m³) before dividing.
All metals have the same density. — Correct: Density varies widely by material — aluminum (2700 kg/m³) is far less dense than gold (19300 kg/m³).
FAQ
What is density?
Density is mass per unit volume, ρ = m/V, telling you how tightly packed a material's matter is.
What is the density formula?
ρ = m/V, where m is mass and V is volume.
What are examples of density?
Water is 1000 kg/m³, gold is 19300 kg/m³, and air is about 1.2 kg/m³.
How to calculate density?
Divide an object's mass by its volume, keeping units consistent (e.g., g/cm³ or kg/m³).