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Every earthquake begins at a single point where rock suddenly shifts. From this point, waves spread out in all directions, compressing and expanding rocks and earth. An earthquake creates different kinds of waves that travel both lengthwise and up and down.

Topics and Connections:

• Earthquakes
• Waves and vibrations

Materials:

• classic metal Slinky

Directions:

Teacher:

• Have students touch their fingers very lightly on the edge of the table while you hit the table sharply (on the top or side). Ask students to describe what they feel. This will introduce the idea that vibrations travel through a medium, whether the tabletop or the Earth.

Students:

• Work in pairs.
• Mark a spot near the middle of the Slinky with a small piece of white tape or some other visible marking. This will make it easier to see how the Slinky is moving.
• Hold each end of the Slinky and stretch the Slinky to a length of about three feet.
• Explore what happens when one end is moved. How many different ways can you move the Slinky, and how many different ways does it respond?
• Compare how vibrations travel through the Slinky and through a tabletop.

Extending the activity:

• Tie this activity to the 'Topple Table' activity: which kind of earthquake wave represents the different motions you made with the lid.
• If you have many Slinkies, you can arrange them so they are all pointing outwards from a common center (you may need to move some tables around to do this). Tie the Slinkies together with a string. Jerk the Slinkies where they're joined. The motion spreading out from this point will show how earthquake waves spread out in all directions from the epicenter of the quake.

Follow Up:
Introduce the specific vocabulary geologists use:

• The kind of wave you get when you quickly push one end of the Slinky a few inches straight towards your partner–a 'squeezing together' wave–is called a 'P-wave' ('P' for "pressure"), and is the fastest kind of earthquake wave.
• Quickly shifting the one end of the Slinky a few inches to the side and then back, creates a 'moving to the side' wave–an 'S-wave'('s' for 'surface')–and takes longer to spread out from an earthquake.

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