Density

Density

· Density is a physical property used to compare objects by the amount of particles packed into them.

· This is different from specific gravity, which compares everything to water.

Example

· Is it gold or brass?

^· Gold density = 18.5 g/cm³

· Brass density = 8.5 g/cm³

· Gold is more dense than brass because it has more than twice as many particles packed into the same amount of space.

Density in solids, liquids, gas

· Density can be compared in solids, liquids, and gasses.

Calculating Density

· Density is calculated by dividing mass by volume:

D = M/V or M = DV

Units

Usually:

· unit for mass is grams (g)

· unit for volume is cubic centimeters (cm³) or milliliters (ml). Remember 1 cm³ = 1 ml.

· Therefore, the units for density are usually grams per cubic centimeter (g/cm³) or grams per milliliter (g/ml).

Float or Sink

· The density of water is 1 g/ml.

· Objects float if they have a density less than water (< g/ml).

^· Objects sink if they have a density greater than water (> 1 g/ml).

Example - Ice is an exception

· Frozen water (ice) has a density of 0.91 g/cm³.

· Since the density of ice is less than the density of water it floats

· Except for water, the solid state of a substance is more dense than its liquid state

Temperature Affects Density

· Density can be affected by temperature.

· When temperature increases, density decreases.

· When temperature decreases, density increases.