
Your Objectives:
 Use the density formula to correctly figure the density of
granite (continents) and basalt (ocean).
 We will discuss why the ocean floor (basalt) is lower than
the continents (granite).
 Correctly differentiate between very salty water (most
dense) and less salty water.
What letter
corresponds to
each number?
1)
2)
3)
4)
____ High Tide
____ Neap Tide
____ Low Tide
____ Spring Tide
Answers
1) C
2) B
3) D
4) A
a)
b)
c)
d)
Higher high tide and lower
low tide cause by
alignment of sun, earth
and moon (during full and
new moons)
Lower high tide and higher
low tide caused by 90
degree alignment of sun,
earth, and moon (during
first and third quarter
moons)
Bulge in the ocean on the
side facing the moon and
on the opposite side.
Lowest level of the ocean
that occurs between the
two high tides.
The continents are formed mainly out of
granite rocks.
 The ocean floor consists of rocks called
basalt.
 Why does the ocean floor sink lower into
the mantle than the continents?


Density Demo
Granite is igneous rock that is formed
when magma solidifies within the crust or
mantle.
 Granite is about 3.8 billion years old.
 Basalt hardly ever exceeds .1 billion years
old. Why?

This is because the oceanic crust is constantly being
replaced with molten material that climbs upward from
the mantle.
The reason that the continents stand higher
than the ocean basins is that the oceanic
crust is more dense (3.2 g/cm³) than the
continental crust (2.7 g/cm³).
 The oceans take up 3/4 (.71%) of the earth's
surface.
 What is in the ocean?

Salty water, diverse life forms, dissolved gases, minerals, and
nutrients.
Demo
 Why did the egg sink to the bottom in the
first container?
 Why did the egg float in the second
container?

Salinity: The amount of dissolved salts in the
water
 Temperature and Salinity affect the density
of water.
 Very salty waters are more dense and will
sink lower in the ocean.
 Less salty water is less dense and will float on
top of more dense salty water.


We used the density formula to figure out the
continents density and oceans density.
 What is the formula?
 Which is more dense?
We learned how the oceans salinity affects the
density of water.
This information will be useful for studying for the
test tomorrow.
Any questions?

Starting Tuesday, we begin Physics!
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