Density Presentation 1 [.pdf] - Earthguide

Mission Bay High School
Density as a Force
that drives Earth
Science Process

Theme
Relative density and convection in earth
systems
• Gases: atmosphere
• Liquids: water in lakes and oceans
• Deformable solids: earth’s crust and mantle
• In lab experiments
• Tie to real world examples
Big idea

What is density?
What is convection?
Focus questions
What is the relationship between relative
density and convection?
Which earth materials (air, water, rocks)
convect?
How does convection influence weather?
Ocean circulation? Earth’s crust and mantle?
What happens to the process of convection
under low gravity conditions (for example in
space)?

Your job
Work in teams
Work though the experiments
Keep accurate lab notes
Calculate values from measured
results
Participate in small group and
large group discussion

Outline
Outline: in 4 bullets
• Relative density and convection in
water.
• Relative density in air; importance
of heat capacity.
• Relative density of rocks (Plate Tectonics)
• Seismic energy propagation

Tie in-lab experiments to real
world processes
Cuyamacha Lake

Experiment 1
Influence of temperature on density
engage Cuyamacha Lake
Is the water in the lake more dense or less
dense in the summer than in the winter?
Day/night?
Which part of the lake (surface or bottom)
changes temperature first when solar
radiation changes?
How might solar radiation and air temperature
change from summer to winter (or day to
night) affect circulation in the lake?
Why is water circulation in the lake important
for fish populations?

Experiment 1
Cool water
to 5 o C
ice
Hot plate
Using dropper, carefully add
colored hot water to cold water
Observe layering
Record data
Heat water
to 40 o C
Add food
coloring to
hot water

http://terraserver.microsoft.com/
Pacific
Ocean
San Diego River

Experiment Experiment 2
Influence Influence of composition composition on density
density
engage
Is San Diego river water more saline or less saline
than the Pacific Ocean seawater?
Is river denser or less dense than seawater? Why?
How might the distribution of river water and
seawater at the mouth of the river be different on a
rainy day than on a sunny day?
How might the distribution of river water and
seawater be different when the tide is rising than
when it is falling?
Why is the distribution of salinity (and density of the
water) in the San Diego river important for the plants
and animals that live there?

Experiment 2
Measure salinity using the refractometer
fresh water salt water
Add food
coloring to
salt water
Gently and carefully
transfer salt water
Use a dropper or pour
Observe layers
Record data

Experiment 3
Convection
engage
What do you think happens when
a pan of water is heated on one
side and cooled on the other side?
Why?
How might uneven heating affect
the currents in the oceans?

Experiment 3
red food color blue food color
50 o C 0 o C
Record observations

Iced water Heated water

explain
What is THERMOHALINE
circulation?
Why is thermohaline circulation
important in lakes?
Why is thermohaline circulation
important in the ocean?

Science magazine July 2005

Relative Relative density density and convection
convection
in the atmosphere
atmosphere
Focus questions
What causes air to rise?
What causes air to fall?
Why do coastal regions have more
moderate climate than inland
regions?

http://prism.asu.edu/clouds/movies/rain.mov

Experiment 4
Temperature
inside
beaker?
Temperature
outside
column?
Water and dry ice
Put column over dry ice
Observe direction of
vapor flow
Remove column
Observe the direction of
vapor flow
Record data
Wear glove to
handle dry ice!!!

extend
Is the direction of vapor flow in your
beaker/PVC column experiment more
similar to what happens when
cumulonimbus clouds form over the
Laguna Mountains in late summer or
more similar to what happens to air
masses that flow from glaciers? Why?