d. Place two empty soda cans upright on either side of the cord on the
center tape line. Both cans should be the same distance from the
cord—about 30 cm (1 ft). When a wave of sufficient amplitude is sent
along the cord between these cans, what will happen? (The same piece
of cord, as indicated by the colored tape marker, will knock over both
cans.)
2. Point out that although students may only see motion in one
direction, the transverse wave they have just observed vibrates in a
direction perpendicular to its direction of motion. Remind students
that S waves within the Earth are not just in one plane, and don’t all
have the same frequencies and amplitudes. In an earthquake, a jumble
of S waves passes through a particular volume of Earth at the same
time. Since S waves reach the surface from below, a special pendulum
seismograph would show ground motion for S waves as a very
complex, seemingly random pattern of horizontal (back and forth)
motions.
C. Conclusion
Ask students:
Q
Which type of wave does this activity illustrate? (S waves)
Q
What are some differences between P waves and S waves? (P
waves are longitudinal and S waves are transverse. P waves can be
transmitted through solids, liquids, and gases, while S waves can
only be transmitted through solids.)
Now ask students, working in the same pairs as for part one, to decide
what a diagram of an S wave would look like and draw one on the
other half of the page they used in part one. They may want to revise
their drawings of a P wave at this time. When they have finished, ask
each pair of students to exchange their drawings with another pair and
discuss the similarities and differences.
ADA P T A T I ON S AND E X T E N S I ON S
1. If students have also discussed Rayleigh waves and Love waves,
ask them to draw these on the backs of their pages at this time and
follow the procedure for exchanging diagrams as above.
2. Invite students to research and discuss the intermolecular forces that
provide the means of transmitting energy in transverse waves, and
why S waves can not be transmitted through liquids, including Earth’s
outer core.
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