BACKGROUND:
This lab focuses on the movement of
ocean water, which is a difficult principle to explain and understand.
Although wind, the movement of the Earth, and the differences between hot
and cold water are the major factors that determine the direction of the
ocean currents, topography and salinity also play a part. This lab
only looks at two factors: the movement of the Earth and the differences
between hot and cold water.
The differences between hot and cold water
can cause movement. Warm water rises and as it cools it gets heavier
and sinks. This motion is called a convection cell. In the
oceans there are many areas that have cold water, especially in the polar
areas. This cold water moves along the bottom of the oceans until
there is an opportunity to rise, and when this occurs it is called upwelling.
The reasons for water rising are numerous. Emphasize that there is
motion caused by this temperature difference.
The Coriolis Motion occurs as the Earth rotates,
creating a movement in the ocean. In the northern hemisphere water
particles move to the right; in the southern hemisphere water particles
move to the left. This lab is meant to introduce the concepts,
and not for the students to fully understand the complex mechanisms that
are occurring.
PROCEDURE:
EXERCISE I.
Complete
the demonstration using the hot and cold sea water as shown on the student's
lab sheets. Let the students record what is happening in their lab
manual. Point out that there are many factors that influence the
movement of the water. This "convection" caused by heat, is just
one way.
EXERCISE II.
- Place cardboard base
on table top.
- Place piece of heavy construction
paper in middle of base.
- Firmly place nail or pin through
center of construction paper (being careful not to allow nail head
to come through).
- Fill medicine dropper with water.
- Turn nail upside down (head facing table)
and spin like a top with the construction paper spinning on
top of heavy cardboard base.
- As the construction paper is spinning,
the second partner will drop 1-3 drops of water as close to
the nail as possible.
Have the students change the direction
of the spin and record what happens. This demonstrates that a moving
"sphere" deflects particles because of the motion. This is the same
thing on the Earth, except the water can't just "fly" off.
