Slinkies as Seismic Waves: Teacher Handout
Slinkies as Seismic Waves, will help students visualize how seismic waves propagate (travel) through the
earth. There are 2 types of seismic energy: P-waves (pressure waves) and S-waves (shear waves). Seismic
surface waves are formed when P- and/or S-waves interact (collide) near the earth’s surface.
Seismic waves are generated at the source location of the earthquake. The seismic wave energy moves out
radially from the source, in the same way that ripples move away from the location of a stone (the source)
thrown into a pond. P- and S-waves travel at different speeds through the earth and with different wave
motions. The activities described below are designed to help you visualize these different motions.
P–Waves, also called Pressure Waves or Primary Waves
P-waves are the fastest waves and are the first waves recorded by
seismographs. Some call P-waves push-pull waves because of the
way they contract and expand while travelling through the earth.
P-waves work to compress material. However, the material resists being compressed, or squished, and
moves the energy to the surrounding area.
To visualize this, you will need one slinky and preferably a partner. You can do this on your own by tying
one end of the slinky to the base of a chair leg or table leg.
Working with your partner, each hold an end of the Slinky and stretch it out on the floor until it is about 2
meters (6 ft) long.
6 ft Apart
Select one person in each pair to be ‘the earthquake’, and instruct this person to pull the slinky toward them
and then push away.
Describe what the slinky is doing. Count how long it takes for the ‘earthquake’ to move from one end of
the slinky to the other. Using paper and pencil record the travel time for the P-wave to travel from one
person to another, make several measurements so you can assess the uncertainties.
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S–Waves, also called Shear Waves or Secondary Waves
S-waves travel by distorting the material. S-waves cannot propagate
through liquids or gases because they require rigidity in the materials
they can travel through.
To visualize how S-waves propagate, again, stretch out the slinky on the ground about 2 meters (6 ft)
between you and your partner or attach one end to the base of a chair leg or table leg.
6 ft Apart
Have one person hold the
slinky end in one spot
(don’t move!) instruct the
person at the other end
of the slinky to shake it
from side to side or up
and down.
Describe what the slinky is doing. Count how long it takes for the ‘earthquake’ to move from one end of the
slinky to the other. Using paper and pencil record the travel time for the S-wave to travel from one person
to another, make several measurements so you can assess the uncertainties.
Seismic Stations, locations where seismologist record seismic data
There are thousands of seismic stations in the world recording data 24 hours a day,
everyday. These stations can record up/down motion, east/west motion and north/
south motion.
To learn more about the types of data these stations can record form groups of 5 people.
Two of these people will be the start/end of the slinkies as above. The remaining three people will be given
tape of different colors (folded post-it notes flags of different colors will also work) and asked to affix the
tape to one rung of the slinky, at the location of their choice. (Continued on next page)
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These colored markers represent the location of seismic recording stations. Repeat the steps above simulating P- and S-waves.
What is happening to the tape? If the tape was a data recording pen what shape would the pen draw for the
P-wave passage? What shape for the S-wave passage? Compare and contrast the two types of seismic
waves and discuss what you observed at the different seismic stations (i.e., colored tape.)
Things that you and your students might have noticed:
P-waves:
each ring of the slinky moves parallel to the line
connecting the partners (e.g., toward and away)
-
the P-wave travels faster than for the S-wave
S-waves:
each ring of the slinky moves perpendicular to
the line connecting the partners
-
the S-wave travelled more slowly than the P-wave
Seismic stations:
The station closest (farthest) to the earthquake moves first (last)
The station moves more (bigger amplitudes) for S-waves than P-waves
Slinkies as Seismic Waves is a set of activities that serve as a partner to the University of Utah Seismograph
Stations (UUSS) travelling exhibit “Earthquakes in the Intermountain West”. You may also find it helpful
with curriculum related to teaching geology, plate tectonics, faults, and earthquakes. For those in Utah
wishing to book the exhibit or tour UUSS, please contact Exhibit Coordinator, Marcela Torres:
[email protected], 801-585-0354.
Visit UUSS online http://quake.utah.edu/.
For additional geoscience teaching tools please visit http://idaweb.ucsd.edu/~dkilb/EducationLinks.html
This material is based upon work supported by the National Science Foundation under Grant Number EAR-1053376.
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You Try It!
Formula: Distance = Rate * Time
Fact: Typically P-waves travel at a rate of 6 km/sec or ~3.7 miles/sec
Fact: Typically S-waves travel at a rate of 4 km/sec or ~2.5 miles/sec
Question 1
Using Google Maps approximate the distance in miles between where you live and
your school?
Question 2
Using Google Maps approximate the distance in miles between where you live and
Disneyland?
Question 3
Compute how much time it would take for a P-wave to travel from where you live to your
school?
Question 4
Compute how much time it would take for a S-wave to travel from where you live to your
school?
Question 5
Compute how much time it would take for a P-wave to travel from your school to Disneyland?
Question 6
Compute how much time it would take for a S-wave to travel from your school to Disneyland?
Question 7
Find the most recent 3 largest earthquakes, include Latitude and Longitude and magnitude?
Question 8
Compute how much time it would take for the P-Wave of each earthquake to reach your school?
Need a hint? The formula can be re-written as: Time = Distance / Rate
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