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Cornell Notes 4.1
Density
December 21, 2011
Pages 115 and
117
Density
• Density describes how much mass is in a
given volume of a material.
Mass and Volume
• Remember that mass is defined as how
much matter something has.
• Volume is the amount of space an object
takes up.
Shotput: Big Mass,
Small Volume
Beach Ball: Small
Mass, Big Volume
What is Density?
• Density really means how crowded the
atoms are in a given substance
Dense
Not So Dense
Density
• Solids, liquids and
gases are matter, so
they all have density.
Density
• The units used for
density depends
on whether the
substance is solid
or liquid.
– For liquids use
units of grams per
milliliter (g/mL)
– For solids use
density in units of
g/cm3 or kg/m3.
Density of common materials
• Density is a property of material
independent of quantity or shape.
Density of common materials
• Liquids tend to be less
dense than solids of
the same material.
• Water is an exception
to this rule.
• The density of solid
water, or ice, is less
than the density of
liquid water.
Finding Density
•
To find the density of a
material, you need to know
the mass and volume of a
solid sample of the material.
1. Mass is measured with a
balance or scale.
2. Use the displacement method
or calculate the volume.
Finding Density
•
When calculating volume, all of the
units of length involved in the
calculation must be the same.
The Formula for Density
• The formula for density is…
• Density = Mass ÷ Volume
•D=m/v
Life and Density
• Note that if volume is constant, then more
mass means more density
• On the other hand, if mass is constant,
then more volume means less density!
Why density varies
Density changes for different substances
because:
1. Atoms have different masses.
2. Atoms may be “packed” tightly or loosely.