DENSITY

Density NotesWe are likely to say that lead is "heavier" than wood, or that a stone is "heavier" than water.

A little thought reveals that these terms are not accurate. After all, a tree is heavier than a bullet and a pail full of water is heavier than a pebble. What we really mean is that a piece of lead is heavier than a piece of wood of the same size (volume).

The term density is used to describe the relationship between mass (weight) of an object and its volume.

Density: Density is the ratio between mass and volume:

Density= Mass = m Volume V

Common units of Density:g/mL = g/cm3 kg/m3

1 cm3=1 mL 1 dm3=1L Ex: If something has a density of 9 g/ml, that means that for every 9 grams of the substance, takes up 1 milliliter of space.

Mass vs. Weight

• Mass: Amount of matter in a substance.

• Don’t confuse with weight.• Weight: the force with which the earth

pulls (Gravity) on the substance.

• Volume: The amount of space that a substance or object occupies.

QuestionWhich weighs more?50 kilograms of iron Or 50 kilograms of feathers.

BOTH WEIGHS THE SAME. BOTH ARE 50 Kg each.

Question Which has a greater

density? iron Or feathers.

Iron: b/c molecules that make up the iron are more tightly packed for given volume

Density as a Function of Temperature

For most substances, as temperature increases the volume increases and as a result the density decreases.

Density of Water

Density of Water

At 4oC water has its maximum density of1g/cm3

Convert to kg/m3:

Which is denser and why? Ice or liquid water.

1000kg/m3

Most liquids are more dense than their frozen versions, but water is a rare and important exception. Ice is denser.

Note

• Density is an intensive physical property.

(Does not depend on amount of matter in the sample)

Density Column

• Galilean Thermometer