Slinky Lab- Simulating the Motion of Earthquake Waves.
Grade level(s):Grade 6
Motion of earthquake waves, comparing P-waves and S-waves, which are used in locating the epicenter of earthquakes.
Primary wave, P-wave, Secondary wave, S-wave, Surface Wave, L-waves, compression, longitudinal, transverse, epicenter, seismic
What you need:
Slinkies (1 per each group of 3 students), (SEP item #E238)
Stop-watch timers (SEP item # E321)
3 students per group. With each student getting to do different jobs, during each trial, rotating jobs between trials.
- one student is the timer (times the wave as it travels from one end to the other and back again)
- one student is holder (holds the slinky firmly while the last student creates the wave).
- one student is the wave generator (making either the push-pull, P-wave or the side to side, S-wave)
Classroom or outside (blacktop). In order to properly simulate the waves the activity needs to be done in area without carpet or grass, which could dampen the waves.
One class period (45-50 minutes)
Students use a slinky to model earthquake waves. Learn the speed, direction and behavior of different waves which tell scientists about earthquakes.
Basic understandings of earthquakes:
- Layers of the earth
- Plate Tectonics - plate movement, continental drift, plate boundaries
- Different types of faults -transform (including strike-slip), divergent, convergent (including thrust)
- That earthquakes are caused when energy is released as the lithosphere (crust and upper mantle) of the earth moves.
Discovering the types of waves produced by earthquakes. Comparing S-waves and P-waves.
Earthquakes and volcanoes are evidence for plate tectonics. Earthquakes are caused when energy is released as the lithosphere (crust and upper mantle) of the Earth moves. Energy is emitted in the form of waves. There are different types of waves, some move faster, slower, sideways, or up and down. A seismograph records these waves on a seismogram. When an earthquake is recorded it is called an earthquake "event."
There are two types of waves you will discuss with the students, P-waves and S-waves. P-waves or primary waves, are the first waves that the seismograph records. The P-wave is the "fast" wave and can be called a push-pull wave, because it moves by contracting and expanding along a horizontal path. A P-wave travels through a material as a compressional force. For example, when you speak, your voice compresses a volume of air. One of the properties of air (and just about any other material) is that it resists being compressed into a smaller volume. When your voice compresses the air, it resists by pushing against neighboring volumes of air. These volumes then resist compression, and they push back against their neighbors. This generates a wave of compression that travels through all the volumes of air between your mouth and the person hearing you.
The second major type of seismic wave is called an S-wave. S-waves are shear waves and move from side-to-side. S-waves are slower than P-waves. The particle motion in shear waves is perpendicular to the direction of the wave.
Give the students a few minutes before they start their trials to play with the slinkies. If they don't they will likely do it during their investigation time. Remind students of the proper way to use the slinkies (safety and taking care of the materials).
Lesson Implementation / Outline
Brainstorm with the students about what they remember about earthquakes, how they are generated from deep inside of the earth and ask how they think scientists locate the epicenter of an earthquake to determine its location.
After dividing the students into groups of 3, discussing safety/appropriate use of materials, and distributing the materials (allowing for play time).
Give the following directions to the students, while demonstrating both the P-wave and the S-wave:
- Begin by stretching the Slinky 2 meters (6 feet) between your partner and yourself. One person will hold each end.
- The other person will be timing the waves on the Slinky (one complete trip, back and forth).
P-WAVES (PUSH & PULL):
- Practice first by pulling the Slinky toward you a bit and then pushing it away. Notice that a wave travels along the Slinky from you to your partner.
- You will do 3 trials of the P-wave, timing the wave as it does one complete trip back and forth. Record the information on the STUDENT SHEET and sketch the movement of the Slinky.
- Take the average (find the mean) of the 3 trial times.
You should see that the vibrating parts of the Slinky move back and forth along the same direction in which the wave is traveling. This type of wave is called a longitudinal wave or a compression wave, and it is a model for seismic primary waves, or p-waves. Theyâ€™re known as primary waves because they are the fastest of the earthquake waves, arriving first at distant points.
If your students haven't moved on to the S-wave after 10-15mins, remind them to do so.
S-WAVES (SIDE TO SIDE):
- Shake one end of the Slinky from side to side. Notice that a different type of wave travels along the Slinky. This time the sections of the Slinky move from side to side (horizontally), but the movement of the Slinky is at right angles to the direction of the progressing wave.
- You will do 3 trials of the S-wave, timing the waves as it dos one complete trip back and forth. Record the information on the STUDENT SHEET and sketch the movement of the Slinky.
- Take the average (find the mean) of the 3 trial times.
This time you should see a type of wave is called a transverse wave. A transverse wave can move through the bulk of a solid although it cannot move through liquid or gas. The transverse wave you made with the Slinky proves a model for seismic waves called secondary waves, or s-waves that travel through solid rock. There are really 2 types of S-waves. S-H (S-Horizontal) waves (which you just demonstrated) and S-V waves (S-Vertical) which you could demonstrate by moving the Slinky up and then down and watching the wave.
Remind the students to sketch how the slinky moves and to record the time for the wave to travel in a complete trip on their STUDENT SHEET. Then they should complete the bottom of the student sheet by answering questions A-C, either with their teammates are as a whole class to understand how the slinky moved, and how that looks in an earthquake.
Move from group to group as they try the different types of waves. Make sure they are making the waves properly: P-wave (push and pull) and S-wave (side to side). Make sure they are sketching and noting the times of the waves. They should see a difference. Ensure that they get to trials of both types of waves.
Have the students discuss the following:
SO WHAT IS GOING ON??? What did they learn? How does it relate to earthquakes?
Information for the teacher and student to read/draw from in the discussion:
When an earthquake begins the stress on large blocks of rock becomes greater than the strength of the rock. The rock breaks, releasing large amounts of energy. This energy is carried outward in all directions by various seismic waves, some of which can reach the opposite side of the earth in about twenty minutes. The further the waves travel from the focus of the earthquake, the weaker they become.
P-waves push and pull the underground rocks, causing structures on the surface to move back and forth. SH-waves move the rocks beneath the earth's surface from side to side, giving buildings on the surface a good shaking, often with very damaging effects. With SV-waves, the shaking is in a vertical direction-which sometimes can be enough to launch you out of your seat. S-waves and P-waves cause high-frequency vibrations that tend to cause low buildings to vibrate more than tall structures.
A different class of seismic waves are surface waves. They are long, slow waves. The low-frequency vibrations that they induce in buildings have more effect on tall buildings than on low ones. Love waves (also named Q-waves) are surface seismic waves that cause horizontal shifting of the earth during an earthquake and shake things from side-to-side. (A.E.H. Love predicted the existence of Love waves mathematically in 1911). The slowest seismic waves, Rayleigh waves, (predicted in 1885 by Lord Rayleigh), are rolling waves that make you feel as if you're struggling to keep your balance on a ship in the open ocean.
Extensions and Reflections
Lessons on finding the epicenter of earthquakes, using seismographs, and earthquake safety can easily follow from this point. In addition, if desired, one could have students average the times across the class as a math exercise, or do research in the the strength and types of waves generated in famous/local earthquakes.
The students I worked with really enjoyed this activity and remembered the types of waves much more clearly after generating them on their own. Be sure to let them play a bit with the slinkies before starting their trials, otherwise they will want to do it during the actual inquiry.
Weblinks and References
|SLINK LAB WAVES.doc||27 KB|
|Student Sheet - Slinky.doc||53.5 KB|