Physical Science / Unit 1: Science Skills and Measurement
1.5 Density
Notes
Density is how much mass is packed into a given volume.
- Formula: $\displaystyle D = \frac{m}{V}$. Units: g/$\text{cm}^3$ or g/mL for solids and liquids.
- Example: A rock has mass 60 g and volume $20 \text{ cm}^3$. $\displaystyle D = \frac{60}{20} = 3 \text{ g/cm}^3$.
- Rearranged: $m = D \times V$ and $\displaystyle V = \frac{m}{D}$.
- Water has a density of $1.0 \text{ g/cm}^3$. Objects less dense than water float; more dense objects sink.
- Density is a property of the material, so cutting an object in half does not change it.
- Volume of an irregular solid can be found by water displacement.
Practice
A metal sample has a mass of 90 g and a volume of $10 \text{ cm}^3$. What is its density?
$\displaystyle D = \frac{90}{10} = 9$.
A liquid has a density of $2.5 \text{ g/mL}$. What is the mass of 40 mL of it?
$m = D \times V = 2.5 \times 40 = 100$.
An object has a density of $0.8 \text{ g/cm}^3$. What happens when it is placed in water?
It is less dense than water ($1.0 \text{ g/cm}^3$), so it floats.
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