TEACHING CLUES AND CUES
If you made the arrows
listed in the materials
section, use them now to
help students visualize
these angles. Explain that the
science of trigonometry deals with
the mathematics of right triangles.
Here you will simply measure and
calculate the forces.
From 0-20 degrees not
much will happen, but
above 20 degrees, the
students should begin to
4. Stop the groups when they have completed the scale measurements
and explain that the ramp breaks the force of gravity up into two
components. Project the transparency of Master 2.4e, Components of
the Force of Gravity, to illustrate. One of the components operates in a
direction perpendicular to the ramp; that is the force they just
measured. The other force operates along the ramp. That is the force
of gravity, which will cause the landslide. These two components of
gravity form two sides of a right triangle. Depending on the angle of
the ramp, the force of friction may or may not cancel the force of
gravity.
5. To investigate the effect of slope on material with and without a
simulated earthquake, ask the students to remove the scale. Show them
how to place the dish of sand upside down at one end of the board
without spilling the sand. First, place the board on top of the dish.
Then, while holding the board down over the dish, carefully flip the
board over. The dish should be upside down on the board with all the
sand still in the dish.
6. When all the groups have accomplished this, ask students to vary
the angle of the ramp as they did before, this time by slowly raising
the end of the board with the dish of sand. Instruct students to record
the height at which the sand starts to slide, then lower the ramp by
about 5 cm and tap on the ramp to simulate an earthquake.
7. Give these instructions to test the effect of water on the sand:
see some distinct motion.
a. Again cover the dish with the board, flip the dish right side up, and
add 225 ml of water to the sand.
b. Flip the dish of wet sand back onto the ramp and repeat step 6 to see
the effect each new angle of the ramp has on the wet sand.
c. Continue to record your data and observations in the Landslide Data
Table. Use the transparency of Master 2.4e, Components of the Force
of Gravity, and Master 2.4d, Landslide Activity Sheet to answer the
questions about force.
C. Conclusion
Allow time for students to respond to the last questions on the
Landslide Activity Sheet, which ask them to develop an explanation
for what they have observed. When they have finished, ask the groups
to share their explanations, being certain to justify their explanations
by citing their data.
Ask the class if they think the work they have just done is similar to
what scientists do. Ask them what the scientific community would do
with a variety of explanations and varying data for the same
procedure. Impress upon students that their investigation is one aspect
of science and their reporting is another. Explain that it would take a
great deal of time and many replications for any of their explanations
to be accepted as a landslide theory. If they try the extension activities
and want to carry their investigation of landslides still further, they
will have to connect this model to real landslide data.
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