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Supplement to this activity

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Demonstrating P and S Waves with a Slinky

Pier Bartow

Klamath Community College

Introductory level seismology in a physical geology course.

Hopefully they will have read the chapter.

This is the hands-on part of a lecture on seismic waves. I have found this to be an eye opener for students. Also, any time you bring a slinky to class the students want to play with it. So, it's fun!

The students can see that I am putting energy into the slinky in two different ways. A quick push down the length of the stretched out slinky demonstrates a pressure wave and a quick flip of the wrist will send a shear wave down the slinky.

This is a simple analog model of P and S seismic waves. The demonstrations allows the students to answer questions about why P waves travel faster than S waves. Also, they can see why P waves can travel through a liquid while S waves cannot.

This is a great exercise to get a group of students working together.

The students can see that I am putting energy into the slinky in two different ways. A quick push down the length of the stretched out slinky demonstrates a pressure wave and a quick flip of the wrist will send a shear wave down the slinky. This allows the students to answer questions about why P waves travel faster than S waves. Also, they can see why P waves can travel through a liquid while S waves cannot.

I first do the demonstration as described above then they break up into groups to experiment for themselves. I provide one slinky for every 4 students. We then talk about the liquid outer core of the Earth and how this would effect seismograph readings around the globe. Then I give a quiz to help them focus on what they have learned.

A short quiz asks the students to explain the differences between P and S waves, and their unique attributes.