VOCABULARY
Body waves:
waves
that move through the
body (rather than the
surface) of the Earth.
A. Introduction
Explain: It is the energy from earthquakes that puts human beings and
human structures in danger. This energy is transmitted through the
Earth in the form of waves. Distribute copies of Master 3.la,
Earthquake Wave Background. Go over the Body Waves section of
the background material with the class.
B. Lesson Development
1. Ask students:
Q
Where is the energy of an earthquake released? (along the fault
plane where tectonic stress is released)
Q
In what form is the energy from an earthquake released? (in the
form of waves)
2. Divide students into pairs or groups of even numbers, depending on
the number of Slinkies available. Direct students to pick up their
Slinkies and mark two spots on each, near the center of the coil, with
white plastic tape. The two pieces of tape should be at the tops of
adjacent loops.
3. Two students will hold each Slinky, one on either end. Instruct them
to stretch it out to a length of approximately three meters on the floor
or a long counter. Have students take turns compressing between 10
and 20 coils and then releasing them rapidly while they continue to
hold the Slinky.
P waves and S waves are body
waves.
Compression:
squeezing, being
made to occupy less space. P waves
are also called compressional waves
because they consist of alternating
compressions and expansions.
Longitudinal waves:
waves that
move particles back and forth in the
some line as the direction of the
wave (P waves).
P waves:
primary waves, arrive at a
station first because they travel
faster than S waves, or secondary
waves. These waves carry energy
through the Earth in the form of
longitudinal waves.
S waves:
secondary waves; waves
that carry energy through the Earth
in the form of very complex patterns
of transverse waves. These waves
move more slowly than P waves (in
which the ground moves parallel to
the direction of the wave). In an
earthquake S waves are usually
bigger than Ps.
Transverse waves:
waves that
vibrate particles in a direction
perpendicular to the wave’s direction
of motion (S waves).
TEACHING CLUES AND CUES
4. After several repetitions, ask students to describe what they saw
happen with the coil and the tape. Then ask:
Activity 3 in lesson 2.4
deals with tsunami,
destructive water waves
often caused by earth-
Q
What kind of earthquake waves does this movement resemble?
(longitudinal body waves, or P waves)
quakes. If you have not taught this
lesson, refer to it now.
Q
How is the movement of the spring like the movement of the
waves? (It moves by contracting and expanding—by compression
and expansion.)
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