Download Density

Density
Density pg. 33
• Density is the amount of matter in a particular
space.
• Essentially, density is how tightly packed the
particles in a substance are
• The closer the molecules are, the more dense the
object.
Which object has the greater density?
Storytime!
– by Martha Marie Day and Anthony Carpi
Sometime around 250 b.c., the Greek
mathematician Archimedes was given the task
of determining whether a craftsman had
defrauded the King of Syracuse by replacing
some of the gold in the King’s crown with
silver. Archimedes thought about the problem
while relaxing in a bathing pool and had an
epiphany. He realized that the amount of
water that spilled over the tub when he got in
was equal in volume to the space that his
body occupied.
This fact suddenly provided him with a method
for differentiating a mixed silver and gold
crown from a pure gold crown. Because a
measure of silver occupies more space than
an equivalent measure of gold, Archimedes
placed the craftsman’s crown and a pure gold
crown of equivalent mass in two tubs of water.
He found that more water spilled over the
sides of the tub when the craftsman’s crown
was submerged. It turned out that the
craftsman had been defrauding the King!
Legend has it that Archimedes was so excited
about his discovery that he ran naked through
the streets of Sicily shouting “Eureka! Eureka!”
(the Greek word for “I have found it!”).
Archimedes had used the concept of density to
expose the fraud. Density is a physical
property of matter that describes the degree
of compactness of a substance – in other
words, how closely packed together the atoms
of an element or molecules of a compound
are. Since different substances have different
densities, density measurements are a useful
means for identifying substances.
Density Equation
• To find the density of an object divide the
mass of the object by the volume.
• The units of density are g/cm3 or g/mL.
Practice Problems
1.
2.
3.
4.
5.
6.
7.
8.
Mass=10g Volume=1mL
Mass=400g Volume=10cm3
Volume=9mL Mass=54g
Length=2cm Width=4cm Height=5cm Mass=80g
Sides of a cube=10cm Mass=50g
Mass=50g Volume=25mL
Volume=1cc Mass=786g
Length=1cm Width=5cm Height=5cm
Mass=100g
Understanding Density
Think about this:
Which is heavier, a pound of rocks
or a pound of cotton balls?
Trick question, right? Both are a
pound so they weigh the same!
Which one do you think would take
up more space though? A pound of
rocks or a pound of cotton balls?
Density
Understanding Density
A pound of cotton balls
would take up a whole
bunch more space than a
pound of rocks. That’s
because the pound of
cotton balls is less dense
than the pound of rocks.
Density
Understanding Density
The molecules in the rocks are
much closer together and more
compact than the molecules in
the cotton balls.
The rocks have more mass and
take up less space than the cotton
balls, therefore the rocks are more
dense.
Density
Eureka! Density
For just a little more help about the density (and a little review on
volume), watch the Eureka! Video (it’s only about 5 minutes).
http://www.youtube.com/watch?v=GMNpPgLT8Fk