Factors Affecting DensityFactors Affecting Density
TemperatureTemperature
• As the temperature of most substances increases– Atoms move faster and spread apart.– Expansion increases the volume which decreases the density
because the mass remains the same.
Colder Warmer
PressurePressure
• Solids– At great depths
below Earth’s surface there is extremely high pressure from the overlying rocks.
– Minerals are compressed• Volume decreases.• Density increases
Fluids Fluids (Particularly gases such as the atmosphere)(Particularly gases such as the atmosphere)
• As pressure decreases, gases expand.• This results in an increase in volume.• Density decreases
Shape and SizeShape and Size
• If the temperature of a material remains constant, the size and shape will not affect it’s density.
• The mass and volume change proportionately.
Al of these Aluminum objects have the same density
Phases of MatterPhases of Matter
• For most substances particles are most closely packed in the solid phase.
• Most materials are densest in their solid phase.
Water is unusual because it is densest as a liquid.
• As liquid water cools, it contracts and becomes denser until it reaches a temperature of 4o Celsius (3.98o C).
• As water cools from 3.98o C to 0o C it expands, becoming less dense.
This has profound implicationsThis has profound implications
• Ice floats resulting in– icebergs floating in
the ocean
– Lakes freezing from the top down.
Expanding water in pipes and cracks in rocks Expanding water in pipes and cracks in rocks will cause them to break apartwill cause them to break apart
The reason for this unusual property is the The reason for this unusual property is the nature of the water molecule.nature of the water molecule.
(1) The molecule’s shape is asymmetrical and polarized.(a) One side is positively charged(b) The other side has a slight
excess of negative charged.
(2) When water is in the liquid state(a) Molecules are moving around.(b) Because of polarity some
molecules are slightly attracted to one another
(c) The are closer together than in most liquids.
When Water FreezesWhen Water Freezes
• Bonding hydrogen atoms are shared between adjacent water molecules.
• An orderly, hexagonal pattern results.• The open honeycomb-like crystal structure contrasts
with the more closely packed molecules in liquid water.
Density is a concept Density is a concept important to geology.important to geology.
A few examples include:A few examples include:
Plate Tectonics – Density is a factor for …Plate Tectonics – Density is a factor for …
Motions associated with plate boundaries
Behavior of seismic wavestraveling through Earth’s interior
Continental Drift
Volcanic and Earthquake Activity
Mantle ConvectionMantle Convection
Behavior of PollutantsBehavior of Pollutants
Oil SpillsOil Spills
Density of Pollutants Affects FlowDensity of Pollutants Affects Flow
Sediments Flowing into the OceanSediments Flowing into the Ocean
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