Embedded Files
Title: SEISMIC WAVES MINI DEMONSTRATION ***(Unfinished)***
(Students will learn about the types of seismic waves produced by earthquakes and how they move the Earth.)
Principle(s) Investigated:
- seismic waves
- earthquakes
Standards: Grade 9
HS-ESS2-3.
HS-PS4-1.
Develop a model based on evidence of Earth’s interior to describe the cycling of matter by thermal convection.
Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media.
Materials:
- Jello (video of jello?)
- Rope
- Slinky
- YouTube videos
- Students (as part of demonstration)
Procedure:
Ask students if they have ever been to a sporting event in a stadium, like a baseball or football game, where the crowd "did the wave"? (Expect most to say "yes") Have all the students do a wave across the classroom, or stand up and make a big circle to do the wave. Point out how you can see the wave move through the students and that they represent the "medium" or material that the wave travels through.
Explain that waves in air, water, and rock transfer energy long distances without moving the constituent particles of these substances very far.
Examples: An ocean wave can travel across an ocean but each individual water molecule only moves a few meters back and forth. A sound wave in air can go tens and hundreds of kilometers, but the air molecules themselves only shift a fraction of a millimeter.
Waves also travel through the earth after an earthquake, these waves are called seismic waves and we are going to learn about the different kinds of seismic waves.
Show the pushing/pulling compressions of the P waves with the slinky (Can have student volunteers). Ask students to write in their journals, draw pictures about what they see as the wave moves down the slinky and then have them discuss with a partner. (like diagram below)
****Show/ Insert video of jello shaking back and forth.
Next show students the up and down motion of an S wave with a rope. Ask students to write in their journals, draw pictures, and then discuss the differences that they see between the two waves.
Select a few students (4 to 5) to help out with a demonstration.
- Demonstration:
- Have students stand in a line and face in one direction with their hands locked in front of them on each other's shoulders. > represent arms outstretched if seen from above and the 0 is the head of student (>0>0>0>0>0)
- Explain that the students are representing atoms in a solid, they are connected by their arms (representing chemical bonds that are holding the atoms in a rigid position)
- From behind give a rush to the last student's back and watch as the energy travels from person to person.
- This represents a P wave, the vibrational motion of the atoms goes the same direction of the seismic wave.
- Explain that where you pushed the last student would be the focus or initial rupture of the earthquake fault line, the energy would then ripple outwards and transfer from atom to atom by way of the chemical bonds that hold them rigid.
- Next have students face in the same direction and link arms (chemical bond). Still representing a solid.
- Grab the end student's arm and swing back and forth hard. Watch as the ripple moves the students form side to side.
- This represented an S wave. The atoms and vibrational movements are moving perpendicular to the direction of propagation of the material. The energy travels through the solid in a shearing (back and forth)motion.
- Next have students face the way they did in the first demonstration of the P waves with their arms outstretched towards the other student's back, but this time they are not touching their shoulders. This is representing a liquid. Atoms are still close to each other, but are not connected by chemical bonds.
- Push last student's back and show how the compressive wave is still sent through all of the atoms.
- Next have students face the same directions and put their arms on their hips, but don't link arms.
- Demonstrate how if you swing the first students arm back and forth, the wave will not continue through the other atoms. S waves do not go through liquids because they do not have chemical bonds to help in the transfer of energy.
- Have students stand in a line and face in one direction with their hands locked in front of them on each other's shoulders. > represent arms outstretched if seen from above and the 0 is the head of student (>0>0>0>0>0)
Show Slideshow Presentation and reiterate the P and S body waves and introduce surface waves.
Show the correlating videos (below) of the waves motions.
Show some pictures of earthquake damage.
Have students write in their journals why they think understanding seismic waves is important. Discuss.
Next class we will be learning how to use seismic waves to find the epicenter of an earthquake and find out how big the earthquake is.
Student prior knowledge:
Students will have some knowledge on tectonic plates and their role in earthquakes and this demonstration will lead the students into learning how to locate an epicenter of an earthquake and measuring the approximate size of earthquakes using seismic waves.
Explanation of demonstration:
Students will learn about the types of seismic waves produced by earthquakes and how they move the Earth. Through the physical demonstration of actually using humans to portray the movement of the waves, the students are able to visualize how the waves (energy) move through different mediums. The slideshow is shown to reiterate what the demonstration showed and to introduce surface waves to the students. Having the students write in their journals allows the students time to reflect on what they learned in the short demonstration.
Questions & Answers:
- Why do you think engineers might be concerned about earthquakes and how seismic waves move through the Earth?
- It is very important that engineers understand the different seismic waves produced during earthquakes and exactly how they cause the Earth to move in order to build architecturally-sound buildings that can hopefully withstand an earthquake.
- Which seismic waves are the most damaging and why?
- Surface waves are the most damaging seismic waves because they are confined to the surface unlike body waves that are able to transfer their energy through the Earth's surface.
- Why are seismic waves an important tool for our understanding of the Earth's interior?
- Since the information recorded on a seismogram tells us how fast body waves are moving when they travel through Earth, we can tell what type of material they're traveling through. We know that P waves can travel both through solids and liquids and S waves can only travel through solids. As body waves travel through the Earth's internal layers, their speed changes, causing the wave to bend and for scientists to come up with theories as to why. In the diagram below we see that the S waves (black line) stops at the liquid outer core, yet the P waves (yellow line) only change course (get refracted).
Applications to Everyday Life:
- Using seismic waves to enhance architectural design:
- During earthquakes, some buildings remain intact, while others completely collapse possibly trapping and killing people inside. This happens because some buildings are not able to withstand the seismic waves produced by the earthquake. Part of being an engineer is to design solutions that make life safer. Architectural engineers build shake tables to test their buildings and want to make sure that the shake tables, to the best of their ability, accurately represent the shaking of the Earth during an earthquake. This is why it is important that engineers understand the different seismic waves produced during earthquakes.
- Using seismic waves to help map the Earth's Interior:
- Since we are unable to dig deep enough into the Earth to see what the inside looks like, scientists are able to use their knowledge of how seismic waves travel through different mediums in order to come up with what the Earth's interior might look like. (See Diagram Above)
- Using Seismic Waves to Locate the epicenters of Earthquakes (future lesson)
- Knowing how fast seismic waves travel through the earth, seismologists (scientists who study the Earth's movement) can calculate the time when the earthquake occurred and its location by comparing the times when shaking was recorded at several seismic stations. An earthquake's epicenter is located using the distances btained from three seismic stations.If you draw a circle on a map around three different seismographs where the radius of each is the distance from that station to the earthquake, the intersection of those three circles is the epicenter. This is called triangulation.
- Understanding how energy travels through different mediums (materials)
Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.
Videos:
Body (P) Waves Videos: https://www.youtube.com/watch?v=2rYjlVPU9U4
http://www-rohan.sdsu.edu/%7Ermellors/lab8/l8pwav2.htm
Body (S) Waves Videos: https://www.youtube.com/watch?v=en4HptC0mQ4
http://www-rohan.sdsu.edu/%7Ermellors/lab8/l8swav2.htm
Surface (Rayleigh) Waves: https://www.youtube.com/watch?v=6yXgfYHAS7c
http://www-rohan.sdsu.edu/%7Ermellors/lab8/l8rwav2.htm
Surface (Love) Waves: https://www.youtube.com/watch?v=t7wJu0Kts7w
All waves: http://www-rohan.sdsu.edu/%7Ermellors/lab8/l8awav2.htm
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