Density
Mass per unit volume of a substance.
Formula
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Example
Mercury has ρ = 13.6 g/cm³, so 10 cm³ weighs 136 g.
How it works
Density tells you how tightly matter is packed into a given space. The formula ρ = m/V works because it compares the amount of mass in an object to the volume it occupies, so two objects of the same size can have very different densities if one contains more mass in that same space. A denser substance has more mass in each unit of volume.
When to use it
Use this formula when you need to find how heavy a substance is for its size, or when comparing different materials such as metals, liquids, or gases. It is also useful for checking whether an object will float or sink in another fluid.
Worked example, step by step
A block of aluminum has a mass of 54 g and a volume of 20 cm³. Use the formula: ρ = m / V Substitute the values: ρ = 54 g / 20 cm³ Calculate: ρ = 2.7 g/cm³ Final answer: the density of the aluminum block is 2.7 g/cm³.
Common mistakes to avoid
- mixing up mass and volume in the formula
- using mismatched units, such as grams with litres or kilograms with cm³
- forgetting to divide by volume and instead multiplying mass and volume
Did You Know?
Density identifies substances — it's how gold is told from cheaper fakes without melting it.
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