Density is mass per unit volume. It's a fundamental property that helps identify substances and explains why objects sink or float.
d = m / V
Density equals mass divided by volume
Common Units:
Units: g, kg, mg
Amount of matter in the object
Units: mL, cm³, L, m³
Space occupied by the object
💡 Note: 1 mL = 1 cm³
d = m / V
m = d × V
V = m / d
| Substance | Density (g/cm³) | State |
|---|---|---|
| Water (4°C) | 1.000 | Liquid |
| Ice (0°C) | 0.917 | Solid |
| Aluminum | 2.70 | Solid |
| Iron | 7.87 | Solid |
| Gold | 19.3 | Solid |
| Mercury | 13.6 | Liquid |
| Air (25°C, 1 atm) | 0.00118 | Gas |
d = m / V
d = 85.0 g / 10.0 cm³
d = 8.50 g/cm³
Answer: d = 8.50 g/cm³
This is close to the density of brass (8.4-8.7 g/cm³) or possibly nickel (8.9 g/cm³).
Objects float if their density is less than the liquid. Ice floats because d(ice) < d(water).
Density is unique to each substance - helps identify unknown materials.
Impurities change density - compare measured vs expected values.
Convert between mass and volume when density is known.
If m is in grams, V must be in mL or cm³ to get g/mL or g/cm³. Don't mix kg with mL!
It's d = m/V, NOT d = V/m. Density is mass PER volume, not volume per mass.
Use mass (g, kg), not weight (N, lbs). Mass is constant; weight varies with gravity.
Density changes with temperature! Hot substances expand (lower density), cold ones contract (higher density).