DENSITY
DEFNITION
• DENSITY:
The mass of a substance per
unit of volume
• In simple terms…How much
“stuff” is in a certain amount
of space
• Weight/amt of space taken up
• Only way to change
density is by changing
the temperature or
pressure
A. Heating an object causes
the density to decrease -atoms expand and
become more spread out
(less tightly packed)
B. Opposite is true for
cooling because atoms
contract
Pressure
A. As pressure increases, the
volume decreases-- atoms
become more tightly packed
causing density to increase
B. The opposite is true for
decreasing pressure because the
atoms are more loosely packed
SUMMARY
• INCREASE TEMPERATURE,
DECREASE DENSITY
• DECREASE TEMPERATURE,
INCREASE DENSITY
• INCREASE PRESSURE,
INCREASE DENSITY
• DECREASE PRESSURE,
DECREASE DENSITY
WATER
• Water is the standard
used to compare the
density of objects
Density of water:
The density of water
when it is most
dense is:
Density of water:
4
expands above
This is because water _______________
Water is most dense at _______°C.
and below this temperature
4°C
THE DENSITY EXCEPTION
• Usually, solids are the most dense
and gases are the least dense
(think of Earth layers)
• When water freezes into ice, the
atoms expand become less
packed
• As a result, ice is less dense than
water
• THIS IS WHY ICE
CUBES FLOAT IN
WATER!
Density of water:
Any material with a density
greater
less than
thanwater
waterwill
will
DENSITY FORMULA
• On the front page of the ESRT (Earth
Science Reference Tables)
• Density= mass/volume
• Use a scale for mass
• Use lxwxh for regular solids
• Use cylinder and displacement method
for irregular solids
• Units:
g/cm3 for reg. solids; g/mL for irreg. objects
•If substance is cut
into pieces or more
is added to it,
nothing happens to
the density- the
atoms are still
packed the same
• Example 1: the density of a
gallon of water is 1.0 g/mL.
the density of a glass of
water is also 1.0 g/mL
• Example 2: a wood block
cut in half has the same
density as the original
wooden block
Phases of Matter & Density- REVIEW
During which phase of matter (solid,
liquid, or gas) are most materials:
A rock has a mass of 240g and a
volume of 12cm³.
Showing all formulas and calculations,
determine the density of the rock.
The box below has a mass of 120g.
Showing all formulas and calculations,
determine the density of the box.
2.0 cm
2.0 cm
10.0 cm
Density of water example:
If an object has a mass of 25g and a volume of
50mL, will it sink or float in liquid water?