Download notes density 1112

10/19/2012
Objectives
To calculate density
To predict how “high density” molecules will
move
To predict how “low density” molecules will
move
What factors can change density?
Predict what will happen when two objects of
different density meet
DENSITY
How this physical property controls continents
Compare and Contrast…
Take a guess…Which is more dense?
Wood or water
Ice or steam
Cold water or hot water
Metal or clay
Hot air or cold air
Freshwater or salt water
Pepsi or Coke Zero
All three cubes are solids and have the same
volume.
But when you look at the molecules you realize that
the molecules take up a different amount of space.
The density of the blocks are different.
Density Vocabulary
Density: compares the mass of an object to
the amount of space it takes up
The density of pure water is 1.0 g/mL
Which color in the diagram at the right is
the most dense? Yellow
Least dense?
Green
Mass: how heavy the object is
Volume: the amount of space an object
takes up
Evaporation: liquid turning into a gas
Composition: what something is made of,
the number of molecules inside
What is density?
Density: compares the mass of an object to the amount
of space it takes up
Mass: how heavy the molecules are
Density of pure water is usually 1.0 g/cm3
More dense
more molecules in a specific
space, tends to sink
Less dense
less molecules in a specific
space, tends to rise
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10/19/2012
Do Gases, Solids, and Liquids have the
same density?
Why does hot air rise?
As molecules heat up, they move
faster and spread out
If the molecules spread out, what
happens to density?
Density decreases (gets smaller),
because the same molecules take up
more space
Consequence: hot air will
rise (like in a hot air
balloons)
Why does cold water sink?
How does composition affect density?
Cold water molecules move
more slowly and stay
closer together
Same mass taking up less
volume= more dense
Which picture is hotter?
If I put both temperatures
of water in the same
container, what would
happen?
How do you calculate density?
Mass (grams)
Volume (cm 3 )
Ex2: If a cube has a mass
of 50 grams and a
volume of 5 cm3, what is
its density?
Salts like NaCl, gases like carbon dioxide (CO2) and oxygen
(O2), and other things
Which is more dense, pure water or ocean water?
Ocean water is more dense. It
has more things dissolved in it.
It has a larger mass to take up
the same space.
Cold water sinks to the
bottom
Density =
Pure water, with no other molecules in it, is rare. Drinking
water and the water in the ocean have many different
types of molecules dissolved in it.
What is dissolved in the ocean water?
Ex1: If a cube has a mass
of 25g but still has only a
5cm3 volume, what is its
density?
Ex3: Which is more dense,
the cube from ex1, or the
cube from ex2?
Pure Water
Ocean Water
Density=1.0 g/cm3
Density=1.025 g/cm3
The more stuff that is dissolved
in the ocean, the more dense it
is.
Why should I care about density?
Rising less dense rocks (like silicates) and sinking dense
metals like iron will explain
LAYERS OF THE EARTH
PLATE BOUDNARIES
Hot water rising and cold water sinking will explain
GLOBAL OCEAN CURRENTS
Hot air rising and cold air sinking will explain
GLOBAL WIND PATTERNS
The interaction of rising and cooling air and water will explain
GLOBAL CLIMACTIC CHANGES
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10/19/2012
Take a guess…Which is more
dense?
Wood or water
Ice or steam
Cold water or hot water
Metal or clay
Hot air or cold air
Freshwater or salt water
Pepsi or Coke Zero
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