Density and Mantle Convection
Blue Type: Read, listen, and think
Black Type: Take notes
A shock wave is high density air
Density = Mass / Volume
A greater density means more
mass in a given volume.
Similar to population density
Population density = Number of people / sq. mi.
Why does smoke rise?
Smoke is less dense than surrounding air. Air is
pulled down by gravity and pushes the smoke up.
Test your understanding
You break a brick in half. How does the
density of ½ brick compare to the density
of the whole brick?
A) Density is half as great.
B) Density stays the same.
C) Density doubles.
D) Impossible to tell.
What is convection?
Convection: The transfer of heat energy by the
movement of matter.
More dense
matter falls
Less dense
matter rises
Convection Current Demo
What is needed for convection?
• Matter that flows: gas, liquid, “plastic”
– “Plastic” = a solid that can flow – Silly putty
• Density that changes as temperature changes
• Room to flow
• A gravitational difference (so denser material
sinks and pushes less dense material up)
Earth’s Interior is HOT!
Earth’s mantle brings heat to
the surface by convection. It
is released where crust
spreads apart.
The plates move a few
cm per year on average.
Convection Currents in the Mantle
Why do we care?
Tsunami, earthquake and volcano predictions
depend on knowing about Earth’s interior.
Test your understanding
Why does fiberglass insulation in your attic help
your house stay warm?
A) It produces heat to keep the attic warm.
B) It reduces air movement.
C) It increases convection.
D) It absorbs radiation from the sun.