Factors Affecting Density

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Factors Affecting Density
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Temperature
Colder Warmer

• 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.

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Pressure

• Solids
• At great depths below Earths surface there is
  extremely high pressure from the overlying rocks.
• Minerals are compressed
• Volume decreases.
• Density increases

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Fluids (Particularly gases such as the
atmosphere)

• As pressure decreases, gases expand.
• This results in an increase in volume.
• Density decreases

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Shape and Size
Al of these Aluminum objects have the same density

• If the temperature of a material remains
  constant, the size and shape will not affect its
  density.
• The mass and volume change proportionately.

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Phases of Matter

• For most substances particles are most closely
  packed in the solid phase.
• Most materials are densest in their solid phase.

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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.

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This has profound implications

• Ice floats resulting in
• icebergs floating in the ocean
• Lakes freezing from the top down.

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Expanding water in pipes and cracks in rocks will
cause them to break apart
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The reason for this unusual property is the
nature of the water molecule.

• The molecules shape is asymmetrical and
  polarized.
• One side is positively charged
• The other side has a slight excess of negative
  charged.
• When water is in the liquid state
• Molecules are moving around.
• Because of polarity some molecules are slightly
  attracted to one another
• The are closer together than in most liquids.

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When 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.

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Density is a concept important to geology.

• A few examples include

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Plate Tectonics Density is a factor for
Motions associated with plate boundaries
Continental Drift
Behavior of seismic waves traveling through
Earths interior
Volcanic and Earthquake Activity
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Mantle Convection
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Behavior of Pollutants
Oil Spills
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Density of Pollutants Affects Flow
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Sediments Flowing into the Ocean