Being P-Waves and S-Waves

Michelle Hall-Wallace (Science Education Solutions, Inc.) and Randall Richardson (University of Arizona, Tucson)
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This page first made public: Aug 10, 2006

This material was originally created for Starting Point:Introductory Geology
and is replicated here as part of the SERC Pedagogic Service.


Modeling P-waves and S-Waves
Have the students get out of their chairs, move into groups of 10-15 in an area where they can stand together in a line standing shoulder to shoulder within their group with their arms across each-other's shoulders. For a P-wave, push the group from one end of the line. All the students will bend, but straighten. For an S-wave, have the person at the end of the line bend at the waist to almost a 90-degree angle and then to stand up straight again. This will force the next person, and then the next person, and so on to do the same.
An alternative way to do this activity is to have the whole class stand up together in a circle and do "the wave" as they would in a football stadium, raising their arms and lowering them as the next person raises his or hers. This is a transverse (S) wave. Then have them do a longitudinal (P) wave by having them gently grip each other's shoulders and having one pull or push the next person in line.

Rates and Reflection
Have student from outside the group measure how long it takes the given wave to propagate, and others to measure the distance. Explain that the time is the period and the distance is the wavelength. What are the frequency and the velocity of the wave? Can the students making the wave speed it up?
You may also want to designate a student in the middle of a chain or move the chain against a rigid surface like a wall to reflect waves. Instead of the wave continuing beyond the point of reflection, it must go back the way it came.

Learning Goals

These exercises will:
  • Help students develop a good understanding of different kinds of seismic waves and their effects
  • Liven up a lecture class (esp. for 8 AM sections)
  • Demonstrate a quantitative idea (wave frequency)

Context for Use

These exercises will work well even in large classes.

Description and Teaching Materials

All you need is room for the students to stand up (often at the edge of a classroom or just outside).

Teaching Notes and Tips

These exercises are short (less than half an hour) and require no materials. Michelle Hall-Wallace suggests having one group model the activity first while the others watch and learn. Students may need reminding to stand with their feet firmly planted and not to push too hard or too suddenly.


Informal. Ask students how the direction of motion corresponds to the direction of wave propagation for the P-wave (parallel) and the S-wave (perpendicular). Additionally, make sure they estimate frequency and velocity.

References and Resources

This exercise is developed from (Hall-Wallace, 2000 ) and (Richardson, 2000 ).