Q
Transparency made from Master 2.4e, Components of the Force of
VOCABULARY
Gravity
Q
Overhead projector
Q
Soil, gravel, or other materials for the extension (
optional
)
Friction:
mechanical
resistance to the motion
of objects or bodies that
touch.
Gravity:
the force of attraction
between any two objects with mass.
Gravity is especially noticeable when
an object of great mass, such as
Earth, attracts an object of lesser
mass.
Landslide:
an abrupt movement of
soil and bedrock downhill in
response to gravity. Landslides can
be triggered by earthquakes or other
natural causes.
Loess:
an unstratified, windblown
mixture of clay, sand, and organic
matter usually crumbly and buff or
yellow-brown in color.
Mass movement:
the movement of
surface material caused by gravity.
Variable:
in a scientific experiment,
the one element that is altered to test
the effect on the rest of the system.
TEACHING CLUES AND CUES
If you do not have
enough scales you may
do this section as a
demonstration. You may
also choose to simply describe the
forces and use the factors in the data
table below to describe how the
measured weight of the material
changes as the angle of the ramp
changes. Whether you do the
weighing or the students do, be sure
to convert pounds into the metric unit
Newtons (2.2 pounds = 9.8
Newtons).
P ROC E DUR E
Teacher Preparation
Assemble slides and/or photos. Assemble the other materials ahead of
time and experiment with them to get a feeling for how various angles
will affect their movement. Cover work surfaces with newspapers.
A. Introduction
Ask the students: Can an earthquake cause a landslide? Promote a
discussion of their experiences and ideas. Show any images you have
gathered of earthquake-related landslides, especially those that have
affected your local environment.
Explain to the students that not all landslides are earthquake related;
many are caused by other natural factors. Landsliding, or mass move-
ment, occurs when the forces that hold materials in place are exceeded
by the force of gravity in the direction of motion. The forces that hold
sand, soil, rocks, and buildings in place are related to the strength of the
materials. The balance of these forces may be affected by the intensity
of ground shaking during an earthquake. The steepness of the slope on
which the materials rest determines how much the force of gravity acts
in the direction of motion.
B. Lesson Development
1. Divide the class into cooperative groups of three or more students.
Distribute one copy of Master 2.4c, Landslide Data Table, to each
group. Ask one member from each group to collect a dish of sand and
the other materials.
2. Tell the students they will be conducting this investigation in a
scientific manner. That is, they are to control the variables, manipulate
only one, and measure or observe the response. When students have
completed the experiment, it is very important that they use only their
results to develop an explanation and that their explanation relates only
to this particular model. Point out that the questions toward the end of
the Landslide Activity Sheet relate to the scientific process they are
employing.
3. Instruct students to set up a ramp, as illustrated on Master 2.4c, and
begin to explore the effect of the ramp’s angle on the weight the scale
reads. Explain that the less weight the scale records, the greater the
force of gravity parallel to the ramp and the weaker the force of friction
that holds the material in place. Give these instructions:
a. Place the scale at the bottom end of the ramp and place a dish of sand
right side up on top of it.
b. Raise one end of the ramp to the height corresponding to the first
angle indicated on the Landslide Data Table. As you move from one
angle to another, record the scale readings in the Landslide Data Table.
A G U
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F E M A
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